Welcome to Hariharan Group




Our research group focuses on various aspects of Physical Organic Chemistry and Biophysical Chemistry to understand the effect of light on organic small molecules and biomolecules. Synthetic efforts to modulate the rate of charge recombination that is monitored using ultrafast spectroscopic techniques is one of the primary interests in our group at IISER Thiruvananthapuram. We also look at the strength of weak interactions in novel crystals using theoretical models such as quantum theory of atoms in molecules and exciton migration using cluster model. A combined effort to synthesise novel and diverse architectures, investigate/regulate the ultrafast processes and understand the theoretical reasons behind the events makes our attempt unique.

Latest update

  • Mahesh gets featured in Chemistry A European Young Chemists Special Issue 2018
  • Our endeavours in populating triplet states continue - new PCCP
  • Vinayak bags best undergraduate researcher medal

Academic Positions

  • Dec. 16 Nov. 16

    Visiting Professor

    University of Wuerzburg, Germany

  • Present Sept. 14

    Associate Professor

    IISER Thiruvananthapuram, School of Chemistry

  • Sept. 14 Jun. 14

    Visiting Professor

    Montana State University, Montana, USA

  • Sept. 14 Jul. 09

    Assistant Professor

    IISER Thiruvananthapuram, School of Chemistry

  • Jul. 09 Mar. 07

    Postdoctoral Fellow

    Northwestern University, Illinois, USA

    Mentor:Prof. Frederick D. Lewis

Education & Training

  • Ph.D. 2006

    Ph.D. in Chemistry

    National Institute for Interdisciplinary Science and Technology, Trivandrum, Kerala

    Title

    Design of Photoactivated DNA Cleaving Agents: Synthesis and Study of Photophysical and Photobiological Properties of Bifunctional Organic Ligands

    Supervisor

    Dr. Danaboyina Ramaiah

  • M.Sc.2000

    Master of Science

    Mahatma Gandhi University, Kottayam, Kerala

  • B.Sc.1998

    Bachelor of Science

    Mahatma Gandhi University, Kottayam, Kerala

Honors, Awards and Fellowships

  • 2017
    Featured in ChemComm Emerging Investigators Issue 2017
  • 2017
    Chemical Society of Japan Distinguished Lectureship Award

    image

    To promote internationalization, the Chemical Society of Japan established "Lectureship Award" in 2007. In 2017, 25 outstanding young chemists were selected from 9 divisions as the "2017 Lectureship Award winners" among large number of applicants. Mahesh received the award under the Photochemistry division.

  • 2016
    Fellow of the Royal Society of Chemistry
  • 2016
    Associate Editor of Photochemical and Photobiological Sciences
  • 2015
    Associate Editor of RSC Advances
  • 2015
    Chartered Chemist and Scientist of the Royal Society of Chemistry
  • 2014
    Asian and Oceanian Photochemistry Association Young Scientist Prize

    image

  • 2014
    Indo-US Science and Technology Forum Fellowship
  • 2013-2016
    Editorial Board Member of Advances in Chemistry
  • 2013
    Kerala State Young Scientist Award

    image

    Prof. Mahesh Hariharan bags Kerala State Young Scientist Award 2013 instituted by the Kerala State Council for Science, Technology and Environment (KSCSTE), in recognition of his outstanding contributions. Mahesh Hariharan had made significant contributions in several areas of photoscience that includes the fundamental understanding of effect of ultraviolet light on DNA. The award comprises a grant of Rs. 50,000, a start-up research grant (upto 50 lakhs) and travel support for presenting the research work at a conference outside the country.

  • 2012
    Editorial Board Member of Dataset Papers in Science
  • 2004
    DST-DAAD Fellowship
  • 2001
    CSIR-Research Scholarship

Physical Organic Chemistry Laboratory

i) Biophysical Chemistry and Photophysics of Biomolecules

Exciton chirality, energy and electron transfer in DNA is explored to mimic natural photosynthetic system. Our attempts to use multiple charge donors/acceptors in DNA have clearly demonstrated enhanced photoinduced charge transport as compared to naked DNA. Using nano-, pico- and femto-second resolved absorption/emission techniques, we probe ultrafast processes such as energy and exciton migration across these architectures.

ii) Artificial Photosynthesis/Femtosecond Spectroscopy

We design/synthesise small molecule based donor-acceptor systems to enhance the lifetime of photoinduced charge separated states in organic molecules. Preliminary efforts led us to an understanding that organised donor or acceptor in the presence of respective counterpart (acceptor/donor) improves the survival time of charged intermediates. Attempts are in progress to create better architectures/strategies to improve the efficiency of photoinduced charge separation.

iii) Photonic Crystals

Dihydrogen and other weak interactions are utilised to tune the opto-electronic properties in crystals. We explore the rate of exciton diffusion in organic crystals of diverse packing. In summary, our group aims at understanding ultrafast processes in organic structures having diverse nearest neighbour interaction. We utilize a combination of weak interactions such C–H•••H–C, C–H•••O, C-H•••pi and pi-pi to create various interplanar angles between the adjacent arenes. Using spectroscopic techniques, we probe ultrafast processes such as energy and exciton migration across these architectures.

Interests

  • Electron transfer in organic donor-acceptor systems
  • DNA charge transfer dynamics
  • Crystal engineering
  • Transient absorption spectroscopy
  • Physical organic chemistry
  • Computational chemistry

2018

60)  Extending the Scope of Carbonyl Facilitated Triplet Excited State towards Visible Light Excitation

S. K. Rajagopal, K. Nagaraj, S. Deb, V. Bhat, D. Sasikumar, E. Sebastian and M. Hariharan*
Journal PaperPhys. Chem. Chem. Phys. 2018, DOI: 10.1039/C8CP01023D

Abstract

A series of extended π-conjugated benzophenone analogs was synthesized through the facile Lewis-acid catalyzed Friedel-Crafts reaction in order to exploit the integral triplet state properties of benzophenone. Extending the π-conjugated plane of the phenyl ring of benzophenone allowed to tune the excitation wavelength from far-UV end (~260 nm) to the visible spectrum (~446 nm). Compared to benzophenone, significant red-shifts in the absorption (up to 450 nm in solution) with high photostability, were established for the synthesized benzophenone analogs. As evident from the density functional theory calculations, expansion of ring size at the aromatic part in benzophenone analogs induces a decrease in the HOMO-LUMO gap. The considerable extension of electron density to the carbonyl group in the LUMO substantiates the triplet nature associated in the benzophenone analogs. By virtue of the properties of carbonyl functionality, an apparent increase in the triplet quantum yield (ΦT = 5.4 to 87.7 %) was observed for benzophenone analogs when compared to the corresponding bare polyaromatic hydrocarbon. The spin-orbit coupling was computationally estimated for the benzophenone analogs to propose pathways for the observed intersystem crossing process. The plausibility to photoexcite the aromatic-ring-fused benzophenone frameworks for triplet activation in the visible range opens the door for a new class of materials for photonic application.

59)  γ-Herringbone Polymorph of TMS-Pentacene: A Potential Material for Enhanced Hole Mobility

Vinayak Bhat, Gopika Gopan, Nanditha G Nair and Mahesh Hariharan*
Journal Paper‎Chem. Eur. J , 10.1002/chem.201800875

Abstract

The introduction of the trialkylsilylethynyl group to the acene core is known to predominantly transform the herringbone structure of pentacene to a slip‐stacked packing. However, in this report, we realize the occurrence of an unforeseen polymorph of 6,13‐bis(trimethylsilylethynyl)pentacene (TMS‐pentacene) with an atypical γ‐herringbone packing arrangement. The intermolecular non‐covalent interactions in the γ‐herringbone polymorph are determined from Hirshfeld surface and QTAIM analyses. Furthermore, a comparative SAPT(0) energy decomposition analysis discloses the role of exchange repulsions that govern the molecular packing in the γ‐herringbone polymorph. Moreover, the computationally predicted electronic coupling and anisotropic mobility reveals the possibility of enhanced hole transport (µh=3.7 cm²V‐¹s‐¹) in the γ-herringbone polymorph in contrast to the reported polymorph with the hole mobility of µh=0.1 cm²V-¹s-¹.

58)  Structure-Packing-Property Correlation of Self-Sorted vs. Interdigitated Assembly in TTF.TCNQ Based Charge-Transport Materials

M. A. Niyas, Remya Ramakrishnan, Vishnu Vijay and Mahesh Hariharan*
Journal Paper‎Chem. Eur. J , 10.1002/chem.201705537

Abstract

Among the various donor-acceptor (D-A) charge transfer cocrystals investigated in the past few decades, tetrathiafulvalene-tetracyanoquinodimethane (F.Q, popularly known as TTF.TCNQ) based cocrystals have fascinated materials chemists owing to its packing and exceptional properties. Here, crystallographic information files of eighteen F.Q based cocrystals were extracted from Cambridge Structural Database and classified into Class 1 (D on D and A on A segregated stacks; F.Q, F1.Q - F6.Q and F.Q1), Class 2 (-A-D-A-D-A-D- mixed stacks; F6a.Q - F11.Q and F.Q2) and Class 3 (-A-D-A-A-D-A-; Class 3a (F12.Q and F13.Q) and -D-D-A-A-D-D-; Class 3b (F14.Q)) systems based on their packing modes. PIXEL calculations revealed that the Q on Q dimer is the energetically most favored dimer in F.Q, the substituents on F capable of forming hydrogen bonding, C...S and other weak intermolecular interactions resulted in the greater stability of F on F dimer for F1.Q - F6.Q (except F2.Q). Band structure of F.Q and F6.Q with high interaction of electronic orbitals between D on D and A on A in segregated stacks were found to be metal-like (band gap, Eg = 0.003 eV) and metallic (overlapping bands in the Fermi level) respectively while the polymorph of F6.Q belonging to Class 2 (F6a.Q) displayed a semiconductor-type band structure (Eg = 0.053 eV). F12.Q of Class 3a exhibited a metal-like band structure (Eg = 0.001 eV).

57)  Excited-state dynamics of mononucleotides and DNA strands in a deep eutectic solvent

Yuyuan Zhang, Kimberly de La Harpe, Mahesh Hariharan and Bern Kohler*
Journal PaperFaraday Discuss., 2018, Advance Article

Abstract

The photophysics of several mono- and oligonucleotides were investigated in a deep eutectic solvent for the first time. The solvent glyceline, prepared as a 1 : 2 mole ratio mixture of choline chloride and glycerol, was used to study excited-state deactivation in a non-aqueous solvent by the use of steady-state and time-resolved spectroscopy. DNA strands in glyceline retain the secondary structures that are present in aqueous solution to some degree, thus enabling a study of the effects of solvent properties on the excited states of stacked bases and stacked base pairs. The excited-state lifetime of the mononucleotide 5′-AMP in glyceline is 630 fs, or twice as long as in aqueous solution. Even slower relaxation is seen for 5′-TMP in glyceline, and a possible triplet state with a lifetime greater than 3 ns is observed. Circular dichroism spectra show that the single strand (dA)18 and the duplex d(AT)9·d(AT)9 adopt similar structures in glyceline and in aqueous solution. Despite having similar conformations in both solvents, femtosecond transient absorption experiments reveal striking changes in the dynamics. Excited-state decay and vibrational cooling generally take place more slowly in glyceline than in water. Additionally, the fraction of long-lived excited states in both oligonucleotide systems is lower in glyceline than in aqueous solution. For a DNA duplex, water is suggested to favor decay pathways involving intrastrand charge separation, while the deep eutectic solvent favors interstrand deactivation channels involving neutral species. Slower solvation dynamics in the viscous deep eutectic solvent may also play a role. These results demonstrate that the dynamics of excitations in stacked bases and stacked base pairs depend not only on conformation, but are also highly sensitive to the solvent.

2017

56)  Enhanced intersystem crossing in carbonylpyrenes

Shinaj K. Rajagopal, Ajith R. Mallia and Mahesh Hariharan*
Journal PaperPhys. Chem. Chem. Phys., 2017, 19, 28225-28231

Abstract

Ultrafast intersystem crossing of carbonylpyrenes in chloroform was investigated by femtosecond pump–probe spectroscopy. When compared to the dominant fluorescence decay pathway in pyrene, carbonyl functionalized pyrenes display near-unity triplet formation upon photoexcitation. The excited singlet state (Sp) undergoes rapid intersystem crossing (kISC) concomitantly with internal conversion (kIC) to lower excited singlet states (Sn) within a timescale of 5–11 ps (1/τ2 = kIC + kISC). Furthermore, intersystem crossing from lower excited singlet states (Sn) proceeds through coupling with receiver triplet states, eventually leading to high triplet quantum yields (ΦT = 97%; tetraacetylpyrene). Followed by internal conversion in the triplet manifolds, phosphorescence decay on a microsecond timescale is observed from the emitter triplet state.

55)  Unsolicited Photoexcited-State Pathways Relegate the Long-Lived Charge Separation in Self-Assembled Nucleobase–Arene Conjugate

Abbey M. Philip, Febin Kuriakose and Mahesh Hariharan*
Journal PaperJ. Phys. Chem. C, 2017, 121, 23259–23267

Abstract

We report a comprehensive analysis of the ultrafast photoexcited-state processes of a nucleobase–arene conjugate, 9-(adenin-9-yl)anthracene (AdAn), in organic solvents. By virtue of the strong base-pairing and π–π interactions, AdAn forms an alternate distichous assembly, wherein the adenines are near-orthogonally flanked to the columnar anthracene-on-anthracene (An–An) stacks. The preliminary photophysical and redox analysis of AdAn in organic solvent reveals a summation of adenine (Ad) and anthracene (An) spectral features with minimal perturbation in the ground-state properties. The frontier molecular orbital analysis suggests favorable charge transfer characteristics in the dyad, which is further corroborated by the negative value of the free energy for electron transfer from 1Ad* to An (ΔGet = −1.25 eV) and Ad to 1An* (ΔGet = −0.12 eV) obtained via Weller analysis. Upon photoexcitation (λex = 266 and 355 nm), self-assembled AdAn reveals the formation of radical ion-pair intermediates (τcrA = 120 ms), which display a solvent polarity dependence as demonstrated via nanosecond and femtosecond transient absorption spectroscopy. The “emergence upon assembly” approach offers segregated trajectories of the charge carriers, i.e. delocalization of the electron through the columnar π-channels of anthracenes and the diffusion of the holes across hydrogen-bonded adenines, resulting in persistent radical ion-pair intermediates. Though the unsolicited photoexcited-state pathways of AdAn lead to undesirable photoproducts, the long-lived charge-separated state from a favorable arrangement of DA stack proposes an elegant DA assembly design for emergent solution processable photofunctional devices.

54)  Long alkyl side-chains impede exciton interaction in organic light harvesting crystals

K. Nagarajan, G. Gopan, R. T. Cheriya and M. Hariharan*
Journal PaperChem. Commun., 2017,53, 7409-7411

Abstract

Side-chains at the imidic position of naphthalimide rendered a firm control over (i) the degrees of π–π overlap and (ii) distances between the perylenimide units in a crystalline naphthalimide–perylenimide dyad as determined using single crystal XRD and Hirshfeld surface analyses. Steady-state and time-resolved electronic spectroscopy in addition to DFT calculations revealed a decline in intermolecular excitonic interaction due to interfering alkyl chains.

53)  Twisted Perylene Diimides with Tunable Redox Properties for Organic Sodium-Ion Batteries

H. Banda; D. Damien; K. Nagarajan; A. Raj, M. Hariharan* and M. M. Shaijumon*
Journal PaperAdv. Energy Mater. 2017, 7, 1701316
image

Abstract

Organic rechargeable batteries gain huge scientific interest owing to the design flexibility and resource renewability of the active materials. However, the low reduction potentials still remain a challenge to compete with the inorganic cathodes. This study demonstrates a simple and efficient approach to tune the redox properties of perylene diimides (PDIs) as high voltage cathodes for organic-based sodium-ion batteries (SIBs). With appropriate electron-withdrawing groups as substituents on perylene diimides, this study shows a remarkable tunability in the discharge potential from 2.1 to 2.6 V versus Na+/Na with a sodium intake of ≈1.6 ions per molecule. Further, this study explores tuning the shape of the voltage profiles by systematically tuning the dihedral angle in the perylene ring and demonstrates a single plateau discharge profile for tetrabromo-substituted perylene diimide (dihedral angles θ1 & θ2 = 38°). Detailed structural analysis and electrochemical studies on substituted PDIs unveil the correlation between molecular structure and voltage profile. The results are promising and offer new avenues to tailor the redox properties of organic electrodes, a step closer toward the realization of greener and sustainable electrochemical storage devices.

52)  Self-Assembled Donor-Acceptor Trefoils: Long-Lived Charge Separated State Through Aggregation

A. R. Mallia and M. Hariharan*
Journal PaperJ. Phys. Chem. C, 2017, 121 (9), pp 4778–4788
image

Abstract

Organic photonic nanostructures, capable of efficient light harvesting and storage, provide new avenues in constructing solution processable solar cells and photovoltaic devices. In this contribution, we demonstrate ca. 104-fold enhancement in the photoinduced charge recombination lifetime (τcra = 2.62 ns) in the aggregated state of donor–acceptor (D–A) dyads and trefoils comprised of triphenylamine and naphthalimide. The D–A dyads and trefoils undergo self-assembly in THF forming spherical/vesicular aggregates dictated by weak co-operative intermolecular interactions in contrast to monomer in CH3CN. Observed long-lived charge transfer intermediates in the aggregated state of triphenylamine-naphthalimide (TN) based conjugates could be attributed to the delocalization of photogenerated charge carriers through D–A stacks. D–A supramolecular architectures thus emerged could serve as promising scaffolds for light harvesting, molecular electronics and photofunctional applications.

51)  Persistent Charge Separated States in Self-Assembled Twisted Non-Symmetric Donor-Acceptor Triad

A. R. Mallia, A. M. Philip, V. Bhat and M. Hariharan*
Journal PaperJ. Phys. Chem. 2017, 121, 4765–4777 (Front Cover)
image

Abstract

Organic materials which can self-assemble into higher-order superstructures have extensive applications in artificial light-harvesting systems, solution-processable bulk-heterojunction solar cells, and photofunctional devices owing to their unique charge transport properties. In this report, we demonstrate a self-assembled nonsymmetric donor–acceptor triad (TAN) composed of triphenylamine (T), anthracene (A), and naphthalimide (N) units, for achieving long-lived charge separation via aggregation. Steric hindrance imposed by diisopropyl groups of naphthalimide and the propeller-shaped triphenylamine unit obstructs planarization in TAN. The quantum theory of atoms in molecules demonstrated the presence of synergistic C–H···π, C–H···H–C, π–π, and C–O···O–C interactions between the adjacent TAN units in the crystalline state, leading to significant electronic coupling (Hab). The nonplanar geometry of the TAN triad in the monoclinic space group dictates a unique antiparallel arrangement between the adjacent TAN units along the b-axis. Solvent polarity dependent Lippert–Mataga and spin density distribution analyses of TAN established the presence of charge transfer interactions in the molecule. Solvent polarity dependent nanosecond and femtosecond transient absorption measurements of TAN revealed ca. 108-fold enhancement in the lifetime of the charge-separated state in the aggregated TAN in CHCl3 (τcra ≈ 11 μs) and THF (τcra ≈ 11.20 μs) when compared to that in monomeric TAN (τcrm < 110 fs) in CH3CN. Extension in lifetime of the charge-separated state in self-assembled TAN could be due to the synergetic effect induced by delocalization of charge carriers across alternate slipped antiparallel (Hab = 13 meV) and antiparallel dimers (Hab = 10 meV) of TAN and the presence of triplet charge-separated states.

50)  Enhanced Intersystem Crossing in Core-Twisted Aromatics

K. Nagarajan, A. R. Mallia, K. Muraleedharan and M. Hariharan*
Journal PaperChem. Sci., 2017, 8, 1776-1782 (Outside Back Cover)
image

Abstract

We describe the design, bottom-up synthesis and X-ray single crystal structure of systematically twisted aromatics 1c and 2d for efficient intersystem crossing. Steric congestion at the cove region creates a nonplanar geometry that induces a significant yield of triplet excited states in the electron-poor core-twisted aromatics 1c and 2d. A systematic increase in the number of twisted regions in 1c and 2d results in a concomitant enhancement in the rate and yield of intersystem crossing, monitored using femtosecond and nanosecond transient absorption spectroscopy. Time-resolved absorption spectroscopic measurements display enhanced triplet quantum yields (ΦT = 10 ± 1% for 1c and ΦT = 30 ± 2% for 2d) in the twisted aromatics when compared to a negligible ΦT (<1%) in the planar analog 3c. Twist-induced spin–orbit coupling via activated out-of-plane C–H/C[double bond, length as m-dash]C vibrations can facilitate the formation of triplet excited states in twisted aromatics 1c and 2d, in contrast to the negligible intersystem crossing in the planar analog 3c. The ease of synthesis, high solubility, access to triplet excited states and strong electron affinity make such imide functionalized core-twisted aromatics desirable materials for organic electronics such as solar cells.

49)  V-shaped Oxydiphthalimides: Side Chain Engineering Regulates Crystallisation-Induced Emission Enhancement

G. Gopan, P. S. Salini, S. Deb and M. Hariharan*
Journal PaperCrystEngComm 2017, 19, 419 (Front Cover)
image

Abstract

Tuning the luminescence properties of solid state materials by controlling the molecular packing in the crystal has played an important role in designing new functional materials. A series of five V-shaped oxydiphthalimides (ODPs) were synthesised. Side-chain engineering has been successfully utilized to systematically tune their luminescence properties in the crystalline state by introducing sterically bulky side-chains at the imidic nitrogen. Fluorescence spectroscopy and single crystal X-ray analyses disclose the effect of conformational twisting and bulkiness of imidic substituents on crystallisation-induced emission enhancement (CIEE). Detailed analysis revealed that the CIEE factor of ODPs shows a linear dependence on the percentage volume of the side-chain.

48)  Crystalline Triphenylamine Substituted Arenes: Solid State Packing and Luminescence Properties

A. R. Mallia, R. Ramakrishnan, M. A. Niyas, R. Sethy and M. Hariharan*
Journal PaperCrystEngComm, 2017, 19, 817 - 825
image

Abstract

The crystal packing and solid state photophysical properties of twisted propeller-shaped triphenylamine (T) incorporated aromatic hydrocarbons [ArT where Ar = benzene (Ph), naphthalene (N), anthracene (A), phenanthrene (Phe), pyrene (Py) and perylene (Pe)] are investigated. The qualitative crystal structure and quantum theory of atoms-in-molecules (QTAIM) analyses revealed the dominant role of intermolecular C–H⋯C interactions in governing the three-dimensional arrangement in ArT crystals. Hirshfeld surface analyses revealed that the triphenylamine-substituted arene (ArT) crystals possess a herringbone motif with ρ (%C–H⋯C/%C⋯C) values varying from 10.4 in PeT to 101.2 in AT. A blue shift of ca. 10–28 nm in the emission maxima for PhT, NT, AT, PheT and PyT is observed in the solid state in comparison to that in dichloromethane while the solid state emission maxima is red shifted (ca. 25–71 nm) compared to that in hexane. A 2.40-fold enhancement in the quantum yield of AT is observed in the solid state relative to the solution state (dichloromethane). Solvent polarity dependent absorption and emission measurements of ArT derivatives along with Lippert–Mataga analyses evidenced the presence of charge transfer interactions between Ar and T units. A precise and systematic understanding of the influence of the crystal structure on the photophysical properties is quintessential to achieve highly efficient organic light emitting diodes and other optoelectronic devices in the near future.

2016

47)  Prolonged Charge Separated States in Twisted Stacks of All-carbon Donor and Acceptor Chromophores

A. M. Philip, A. R. Mallia and M. Hariharan*
Journal PaperJ. Phys. Chem. Lett. 2016, 7, 4751–4756 (ACS Liveslides)
image

Abstract

Twisted donor-on-donor and acceptor-on-acceptor bicontinuous assembly in all-carbon pyren-1-ylaceanthrylene (PA) dyad extends the survival time of the photoinduced radical ion-pair intermediates. Aceanthrylene, a functional analog of C70, acts as a versatile electron acceptor owing to its high electron affinity and visible light absorption. Antithetical trajectories of the excitons in the nonparallel π-ways led to persistent radical ion-pair intermediates in aggregated (τcrA ∼ 1.28 ns) vs monomeric (τcrM ≤ 110 fs) PA dyad as observed using femtosecond transient absorption spectroscopy. Marcus theory of charge transfer rates predicts an ambipolar transport characteristic in crystalline PA, thereby endorsing PA as an all-carbon DA hybrid for nonfullerene photovoltaic applications.

46)  On the Origin of Multiexponential Fluorescence Decays from 2-Aminopurine-Labeled Dinucleotides

J. Remington, A. Philip, M. Hariharan and B. Kohler*
Journal PaperJ. Chem. Phys. 2016, 145, 155101
image

Abstract

The fluorescent probe 2-aminopurine (2Ap) has been used for decades to study local conformational fluctuations in DNA. Steady-state and time-resolved measurements of 2Ap fluorescence have been used to predict specific conformational states through suitable modeling of the quenching of the fluorescence of a 2Ap residue incorporated site-specifically into a DNA strand. The success of this approach has been limited by a lack of understanding of the precise factors responsible for the complex, multiexponential decays observed experimentally. In this study, dinucleotides composed of 2Ap and adenine were studied by the time-correlated single-photon counting technique to investigate the causes of heterogeneous emission kinetics. Contrary to previous reports, we argue that emission from 2Ap that is stacked with a neighboring base contributes negligibly to the emission signals recorded more than 50 ps after excitation, which are instead dominated by emission from unstacked 2Ap. We find that the decay kinetics can be modeled using a continuous lifetime distribution, which arises from the inherent distance dependence of electron transfer rates without the need to postulate a small number of discrete states with decay times derived from multiexponential fits. These results offer a new perspective on the quenching of 2Ap fluorescence and expand the information that can be obtained from experiments.

45)  Columnar/Lamellar Packing in Cocrystals of Arylbipyridines with Diiodoperfluorobenzene

R. Ramakrishnan, A. R. Mallia, M. A. Niyas, R. Sethy and M. Hariharan*
Journal PaperCryst. Growth Des. 2016, 10.1021/acs.cgd.6b00968.
image

Abstract

Stimulated by strongly directional C–I···N noncovalent halogen bonding, π-hole···π and π–π interactions, cocrystals of nonplanar 4-arylated-2,2′-bipyridine (ArB) derivatives with 1,4-diiodo-tetrafluorobenzene (D) were generated which exhibit a promising columnar/lamellar packing arrangement. Hirshfeld surface, quantum theory of atoms in molecules, and electrostatic potential surface analyses were employed to examine the weak intermolecular interactions governing the packing arrangement in ArB crystals and corresponding cocrystals with D (ArB·D). Cocrystals of 4-phenyl-2,2′-bipyridine (PhB) and 4-(naphthalen-1-yl)-2,2′-bipyridine (NaB) with D [PhB·D1, PhB·D2, (NaB)2·D2.5, and (NaB)3·D2] exhibited C–I···N directed infinite one-dimensional chains of alternate ArB and D units. In contrast, C–I···N interactions guide the formation of termolecular complexes in the cocrystal of 4-(phenanthren-9-yl)-2,2′-bipyridine with D (PhenB·D0.5). Successful implementation of C–I···N interactions aided by 2,2′-bipyridine and D enabled the tuning of three-dimensional close packing in planar polyaromatic hydrocarbons into a columnar/lamellar arrangement suitable for optoelectronic devices.

44)  Haloacetylation Driven Transformation of Sandwich Herringbone to Lamellar/Columnar Packing in Pyrene

P. S. Salini, S. K. Rajagopal and M. Hariharan*
Journal PaperCryst. Growth Des. 2016, 10.1021/acs.cgd.6b00919.
image

Abstract

Pyrene-based materials possessing one-dimensional cofacial π–π stacked structural motifs with short interplanar distances can have favorable charge transport properties. In this work, we have realized the switching of sandwich herringbone to lamellar/columnar arrangement by introducing α-haloacetyl substituents in pyrene. Density functional theory calculations showed that the subtle difference in the charge distribution induced by the haloacetyl group plays an important role in regulating the cofacial stacking. Single-crystal X-ray structural analyses and quantum theory of atoms in molecules (QTAIM) analyses revealed the role of dihydrogen contacts, halogen interactions, and hydrogen bonding in extending the columnar/lamellar arrangement in three dimensions. Hirshfeld surface analyses showed γ (lamellar) and β (columnar) packing motifs indicating extensive π–π stacking interaction between pyrene units. Detailed structural analysis revealed a gradual decrease in the intermolecular π–π stacking distance (dπ–π = 3.39 Å) with increasing the polarizability of halogen atom, a characteristic interplanar distance observed in highly oriented pyrolytic graphite (dπ–π = 3.35–3.39 Å).

43)  S•••π, π−π and C−H•••π Contacts Regulate Solid State Fluorescence in Regioisomeric Bisthiazolylpyrenes

S. K. Rajagopal, P. S. Salini and M. Hariharan*
Journal PaperCryst. Growth Des. 2016, 16, 4567–4573.
image

Abstract

The formation of well-defined packing motifs and control of π–π stacking by rationalizing the effects of molecular substitution in π-conjugated organic materials represent a significant challenge in supramolecular design. To explore the influence of the thiazolyl group in the solid state packing and photophysical properties of pyrene, a new class of three regioisomeric bisthiazolylpyrenes (2-2″TP) were designed and synthesized. Single crystal X-ray structure and quantum theory of atoms in molecules analysis revealed the presence of S···π interactions in 2′TP. Hirshfeld analysis showed the γ and β packing motif in 2TP and 2″TP, respectively, due to extensive π–π interactions, observed S···π interactions led to herringbone packing in 2′TP. The diverse packing arrangement of 2-2″TP led to a notable difference in the fluorescence behavior in the crystalline state. 2′TP possessing S···π interaction showed remarkable enhanced emission in the crystalline state compared to the amorphous state, in contrast to 2TP and 2″TP. Our results provide new insight for the rational design and regulation of intermolecular interactions of conjugated heterocyclic aromatics to achieve a diverse degree of orbital overlap between neighboring chromophore units and thereby favorable optoelectronic properties.

42)  Crystallization Induced Green-Yellow-Orange Emitters Based on Benzoylpyrenes

S. K. Rajagopal, V. S. Reddy and M. Hariharan*
Journal PaperCrystEngComm 2016, 18, 5089-5094 (Outside Frontispiece).
image

Abstract

We report the synthesis, X-ray structures and photophysical properties of a few benzoylpyrene (BP) derivatives. Steric hindrance due to incremental benzoyl groups causes a systematic reduction in the orbital overlap (π–π) between vicinal pyrene units affording green-yellow-orange solid-state emitters. Crystallization induced emission could arise from: i) electronic (dipolar/excitonic) interactions, ii) arrested bond rotations, and/or iii) lack of solvation in crystalline 1–4BP (ΦFl ∼ 2–26%) when compared to that in solution (ΦFl ≤ 1%). Our earlier effort [Chem. Commun. 2014, 50, 8644] on progressive acylation, in contrast to benzoylation, results in a gradual increase in the π–π overlap between vicinal pyrenes.

41)  Access to Triplet Excited State in Core-Twisted Perylenediimide

K. Nagarajan, A. R. Mallia, V. S. Reddy and M. Hariharan*
Journal PaperJ. Phys. Chem. C 2016, 120, 8443–8450.
image

Abstract

Solvent-free crystal structure of N,N-bis(propylacetyl)-1,6,7,12-tetrabromoperylene-3,4:9,10-bis(dicarboximide), PDI-Br4, obtained by X-ray diffraction reveals the core-twisted perylene motif having π–π stacks at an interplanar separation of 3.7 Å. Slip-stacked arrangement of PDI units in PDI-Br4 arises due to the presence of bulky bromine atoms. Femtosecond pump–probe measurements of monomeric PDI-Br4 in toluene reveal ultrafast intersystem crossing (τISC < 110 fs) when excited at 400 nm. Triplet quantum yield (ΦT) of 19 ± 1% and 105 ± 5% for PDI-Br4 in toluene and vapor-annealed polycrystalline 60 nm thick film respectively are estimated from nanosecond transient absorption measurements. Quantum chemical calculations show that the combined effects of heavy atom and core-twist in PDI-Br4 can activate the intersystem crossing by altering the singlet–triplet energy gap. Enhanced quantum yield accounts for the singlet fission mediated generation of triplet excited state in the PDI-Br4 thin film.

40)  Crystallization induced enhanced emission in conformational polymorphs of a rotationally flexible molecule

A. R. Mallia, R. Sethy, V. Bhat and M. Hariharan*
Journal PaperJ. Mater. Chem. C 2016, 4, 2931-2935.
image

Abstract

The crystallization of weakly fluorescent 4-amino-2,2′-bipyridine (AMBPY) in solution phase under ambient conditions afforded three fluorescent conformational polymorphs. The marginal increase in the barrier to rotation observed in AMBPY as compared to unsubstituted 2,2′-bipyridine could be attributed to the “buttressing effect” offered by the amino substituent at the meta position. A smaller yet significant difference in energy (0.1–2.6 kJ mol−1) with respect to the global minima facilitates the isolation of AMBPY-I–III polymorphs. A unique nitrogen–nitrogen interaction is observed in two of the polymorphs, namely, AMBPY-I and AMBPY-III, promoted by cooperative C⋯H and N⋯H interactions. A crystallization-induced enhancement (ca. 5–10 fold) in the fluorescence quantum yield of AMBPY polymorphs is observed relative to the solution/amorphous state. Controlling the luminescence properties of molecular solids by tuning their packing arrangements via various interactions is an integral aspect in the construction of novel photo-functional materials.

2015

39)  Nonparallel Stacks of Donor and Acceptor Chromophores Evade Geminate Charge Recombination

A. R. Mallia, P. S. Salini and M. Hariharan*
Journal PaperJ. Am. Chem. Soc. 2015, 137, 15604–15607 (Front Cover and JACS Spotlights).
image

Abstract

We report a nonparallel stacked arrangement of donor–acceptor (D–A) pairs for prolonging the lifetime of photoinduced charge-separated states. Hydrogen–hydrogen steric repulsion in naphthalimide-naphthalene (NIN) dyad destabilizes the planar geometry between the constituent units in solution/ground state. Sterically imposed nonplanar geometry of the dyad allows the access of nonparallel arrangement of the donor and acceptor stacks having triclinic space group in the crystalline state. Antiparallel trajectory of excitons in nonparallel D–A stacks can result in lower probability of geminate charge recombination, upon photoexcitation, thereby resulting in a long-lived charge-separated state. Upon photoexcitation of the NIN dyad, electron transfer from naphthalene to the singlet excited state of naphthalimide moiety results in radical ion pair intermediates that survive >10,000-fold longer in the aggregated state (τcra > 1.2 ns) as compared to that of monomeric dyad (τcrm < 110 fs), monitored using femtosecond transient absorption spectroscopy.We report a nonparallel stacked arrangement of donor–acceptor (D–A) pairs for prolonging the lifetime of photoinduced charge-separated states. Hydrogen–hydrogen steric repulsion in naphthalimide-naphthalene (NIN) dyad destabilizes the planar geometry between the constituent units in solution/ground state. Sterically imposed nonplanar geometry of the dyad allows the access of nonparallel arrangement of the donor and acceptor stacks having triclinic space group in the crystalline state. Antiparallel trajectory of excitons in nonparallel D–A stacks can result in lower probability of geminate charge recombination, upon photoexcitation, thereby resulting in a long-lived charge-separated state. Upon photoexcitation of the NIN dyad, electron transfer from naphthalene to the singlet excited state of naphthalimide moiety results in radical ion pair intermediates that survive >10,000-fold longer in the aggregated state (τcra > 1.2 ns) as compared to that of monomeric dyad (τcrm < 110 fs), monitored using femtosecond transient absorption spectroscopy.

38)  A Polyimide based all-organic sodium ion battery

H. Banda, D. Damien, K. Nagarajan, M. Hariharan and M. M. Shaijumon*
Journal PaperJ. Mater. Chem. A 2015, 3, 10453-10458.
image

Abstract

Developing new approaches to improve the performance of organic electrodes for rechargeable sodium batteries is important. Here, we report studies on N,N′-diamino-3,4,9,10-perylenetetracarboxylic polyimide (PI) as a novel cathode for a sodium battery and demonstrate an all-organic sodium ion battery using this polyimide as the cathode and disodium terephthalate (NaTP) (pre-sodiated) as the anode. The synthesised PI exhibits excellent electrochemical properties, when studied as the cathode for sodium batteries, with a reversible capacity of 126 mA h g−1 along with good capacity retention and rate capability, in the voltage range of 1.5 to 3.5 V vs. Na+/Na. The all-organic sodium ion full cell delivered an initial capacity of 73 mA h g−1, with an average cell voltage of 1.35 V. The attractive electrochemical performance combined with the design flexibility of a PTCDA based PI material, offer new possibilities for the development of efficient all-organic sodium ion batteries.

2014

37)  C–H•••H–C and C–H•••π Contacts Aid Transformation of Dimeric to Monomeric Anthracene in the Solid State

K. Nagarajan, S. K. Rajagopal and M. Hariharan*
Journal PaperCrystEngComm 2014, 16, 8946-8949.
image

Abstract

We report the C–HH–C and C–H⋯π interaction assisted formation of thermodynamically stable blue emissive AP-I from the kinetically stable green emissive AP-II crystal polymorph of 1-(anthracen-9-yl)pyrene (AP). The rotational degree of freedom at the bond between the two constituent chromophores facilitates the formation of conformational polymorphs AP-I and AP-II that can be quantitatively crystallized from ethyl acetate and hexane, respectively.

36)  Progressive Acylation of Pyrene Engineers Solid State Packing and Colour via C–H•••H–C, C–H•••O and π-π Interactions

S. K. Rajagopal, A. M. Philip, K. Nagarajan and M. Hariharan*
Journal PaperChem. Commun. 2014, 50, 8644-8647 (Inside Front Cover).
image

Abstract

Quantum theory of atoms-in-molecules and Hirshfeld surface analyses indicated an increase in the extent of (i) C–H⋯H–C; (ii) C–H⋯O, (iii) π–π interactions and a decrease in the extent of (i) σ–π interaction, (ii) an interplanar angle between the vicinal pyrene units in a series of acetylpyrene derivatives offering blue–green–orange emissive crystals.

35)  Light Harvesting Vesicular Donor-Acceptor Scaffold Limits the Rate of Charge Recombination in the Presence of an Electron Donor Interactions

R. T. Cheriya, A. R. Mallia and M. Hariharan*
Journal PaperEnergy Environ. Sci. 2014, 7, 1661-1669 (Front Cover; Hot Article).
image

Abstract

We report the synthesis and excited state properties of a single component light harvesting donor–acceptor dyad (R/S)-NP(OH)2 containing an α,β-dihydroxypropyl side-chain that can undergo molecule–bilayer–vesicle–gel–crystal transition. By virtue of steric hindrance offered by orthogonal naphthalimide and 2,6-diisopropylphenyl substituents, very weak H-type excitonic interactions between the perylenimide units resulted in high fluorescence quantum yield in the dyad-based metastable vesicular gel having a near-quantitative excitation energy transfer from naphthalimide to perylenimide. Femtosecond transient absorption measurements of the dyad (R/S)-NP(OH)2 : indole co-gel show that the vesicular scaffold promoted extension of the survival time of charge separated states (∼1.4 ns) when compared to ultrafast charge recombination (∼6 ps) in dyad (R/S)-NP(OH)2 : indole solution.

34)  Non-natural G-quadruplex in a Non-natural Environment

S. K. Rajagopal and M. Hariharan*
Journal PaperPhotochem. Photobiol. Sci. 2014, 13, 157-161 (Nick Turro’s Special Issue).
image

Abstract

The biocompatibility as well as the sustainability of a deep eutectic solvent makes it a good substitute for aqueous media in studying biomolecules. Understanding the structure and stability of natural and non-natural G-quadruplexes in aqueous and highly viscous media will be useful in biological and nanodevice applications. We report the synthesis and conformational analysis of a model G-rich oligonucleotide G3T3 and non-natural G-rich sequences Pyr1–Pyr3 in aqueous and highly viscous media. Progressive increases in the loop replacement with a non-natural pyrene linker leads to a systematic increase of the thermal denaturation temperature of the modified G-rich oligonucleotides Pyr1–Pyr3 in 10 mM cacodylate buffer (pH 7.2) containing 100 mM KCl, as monitored using UV-Vis spectroscopy. A circular dichroism signal clearly revealed the formation of a predominantly anti-parallel vs. parallel conformation in the natural G-rich oligonucleotide G3T3 as well as the non-natural G-rich oligonucleotides Pyr1–Pyr3 in 10 mM cacodylate buffer (pH 7.2) containing 100 mM KCl. On the other hand, we observed thermodynamic destabilization of G-rich oligonucleotides in a deep eutectic solvent (DES; 1 : 2 choline chloride–urea) containing 100 mm KCl with an increase in loop replacements. Interestingly, we observed an exclusively parallel G-quadruplex conformation in the case of G3T3 in DES containing 100 mm KCl. While pyrene containing G-rich oligonucleotides Pyr1–Pyr3 exhibited a predominantly parallel vs. anti-parallel G-quadruplex conformation in DES containing 100 mM KCl.

33)  Thymine Photodimer Formation in DNA Hairpins. Unusual Conformations Favor (6-4) vs. (2+2) Adducts

M. Hariharan,* K. Siegmund, C. Saurel, M. McCullagh, G. C. Schatz and F. D. Lewis*
Journal PaperPhotochem. Photobiol. Sci. 2014, 13, 266-271 (Nick Turro’s Special Issue).
image

Abstract

The photochemical reactions of eleven synthetic DNA hairpins possessing a single TT step either in a base-paired stem or in a hexanucleotide linker have been investigated. The major reaction products have been identified as the cis–syn (2 + 2) adduct and the (6 − 4) adduct on the basis of their spectroscopic properties including 1D and 2D NMR spectra, UV spectra and stability or instability to photochemical cleavage. Product quantum yields and ratios determined by HPLC analysis allow the behaviour of the eleven hairpins to be placed into three groups: Group I in which the (2 + 2) adduct is the major product, as is usually the case for DNA, Group II in which comparable amounts of (2 + 2) and (6 − 4) adducts are formed, and Group III in which the major product is the (6 − 4) adduct. The latter behaviour is without precedent in natural or synthetic DNA and appears to be related to the highly fluxional structures of the hairpin reactants. Molecular dynamics simulation of ground state conformations provides quantum yields and product ratios calculated using a single parameter model that are in reasonable agreement with most of the experimental results. Factors which may influence the observed product ratios are discussed.

2013

32)  Thermal Response of DNA Supramolecular Polymers Assembled with Hydrophobic Sticky Ends

M. Hariharan,* Y. Zheng, B. Rybtchinski and F. D. Lewis*
Journal PaperJ. Phys. Chem. B, 2013, 117, 14649–14654.
image

Abstract

We report the self-assembly and thermal dissociation of DNA dumbbell conjugates having a perylenediimide (PDI) linker on each end separated by 6–16 A–T base pairs. In the presence of NaCl these dumbbells form one-dimensional supramolecular assemblies as a consequence of the hydrophobic association of their PDI sticky ends. The dependence of assembly formation on dumbbell concentration, salt concentration, and temperature can be conveniently monitored by UV–vis spectroscopy. The melting of these linear assemblies follows two limiting mechanisms, depending on the length of the dumbbells. Upon heating in the presence of salt, the assemblies formed by the longer dumbbells undergo a sequential transition from assembly to base-paired monomer to random coiled monomer, whereas the assemblies formed by the shorter dumbbells undergo disassembly and base-pair melting cooperatively. In all cases, the intramolecular hydrophobic association of the PDI chromophores is observed at elevated temperature. The thermal behavior of these one-dimensional assemblies is compared to that of other sticky-ended assemblies.

31)  Perylene Polyimide Based Organic Electrode Materials for Rechargeable Lithium Batteries

P. Sharma, D. Damien, K. Nagarajan, M. M. Shaijumon,* and M. Hariharan*
Journal PaperJ. Phys. Chem. Lett., 2013, 4, 3192–3197 (One of the most read articles).
image

Abstract

Organic materials for Li-ion battery application continue gaining attention due the virtue of low cost, environmental benignity, and so on. A new class of electroactive organic material called polyimides is particularly important due to the extra stability exhibited at higher current rates. High-performance rechargeable lithium battery cathodes based on polyimides of 3,4,9,10-perylenetetracarboxylicacid-dianhydride are prepared. The novel electrodes exhibit good rate capability and improved cycling stability, which result from their combined beneficial properties such as the presence of additional carbonyl groups, favorable band gap, and enhanced conductivity, making it a potential material for greener and sustainable electrochemical storage devices.

30)  Breakdown of Exciton Splitting through Electron Donor–Acceptor Interaction: A Caveat for the Application of Exciton Chirality Method in Macromolecules

J. Joy, R. T. Cheriya, K. Nagarajan, A. Shaji, and M. Hariharan*
Journal PaperJ. Phys. Chem. C, 2013, 117, 17927–17939.
image

Abstract

Circular dichroism spectra for a series of structurally analogous hairpin oligonucleotides, tethered at the 5′-end with an axially chiral naphthalenimide-perylenimide dyad (NP), is dependent on the nature (AT vs GC) and the orientation (5′-C vs 5′-G) of the adjacent base pair that stacks with the dyad. Charge transfer (CT) interaction between the naphthalenimide unit of the dyad NP and the adjacent guanine–cytosine (5′-C) base pair has been characterized by UV–vis absorption and fluorescence measurements. Molecular dynamics simulations of the dyad end-capped hairpin DNA ODN6i and TD-DFT calculations of the naphthalenimide and perylenimide units confirm that the CT transition dipole orients perpendicular to the perylenimide transition dipole. The orthogonality of the cross product of the CT and the perylenimide transition dipoles with the displacement vector connecting the two dipoles in space results in the zeroing out of the rotational strength of the perylenimide transition dipole, subsequently leading to the DNA-induced nonexciton coupled circular dichroism corresponding to perylenimide, in concurrence with experimental CD spectrum. Singular value decomposition of thermal denaturation of the hairpin DNA having CT interaction (ODN6i) revealed the denaturation proceeded through an additional intermediary stage compared to the hairpin DNA without the CT interaction (ODN6). Dissimilar CD (induced CD for ODN6i vs exciton-coupled CD for ODN6) spectra corresponding to perylenimide unit obtained for similar NP end-capped hairpin DNA sequences cautions against the indiscriminate use of the exciton chirality method, particularly in systems like DNA and proteins containing polarizable chromophores that can interact with reporter transition dipoles.

39)  Single Component Organic Light-Harvesting Red Luminescent Crystal

R. T. Cheriya, K. Nagarajan and M. Hariharan*
Journal PaperJ. Phys. Chem. C, 2013, 117, 3240-3248.
image

Abstract

Highly efficient photoinduced energy transfer is observed in an orthogonal bichromophore naphthalenimide-perylenimide (NP), leading to strong solid-state luminescence (Φ = 0.5 ± 0.04) in the red region (λem = 631 nm). Steric hindrance imparted by orthogonal naphthalenimide and diisopropyl phenyl units prevents the association of perylenimide moieties, thereby retaining a high quantum yield of fluorescence emission even in the crystalline state. Upon photoexcitation at 340 nm, the intramolecular parallel orientation of the transition dipoles permits efficient Coulombic coupling between naphthalenimide and perylenimide in combination with weak H-type excitonic interactions between the intermolecular perylenimide units that results in intense red fluorescence in the crystalline state of dyad NP. Negligible photoinduced electron transfer from the singlet excited state of the perylenimide to the naphthalenimide unit (ΔG = 0.44 eV) and a marginal feasibility (ca. 10%) of photoinduced electron transfer from the singlet excited state of the naphthalenimide to the peryleninimide unit (ΔG = −0.17 eV) makes the dyad strongly fluorescent when excited at both 340 and 475 nm, corresponding to the naphthalenimide and perylenimide units, respectively. A narrow emission at 631 nm, wide absorption window (300–600 nm), and high fluorescence quantum yield in the crystalline state make the dyad NP a potential candidate for optoelectronic and photonic applications.

2012

28)  DNA-Enforced Conformational Restriction of an Atropisomer

R. T. Cheriya, J. Joy, S. K. Rajagopal, K. Nagarajan and M. Hariharan*
Journal PaperJ. Phys. Chem. C, 2012, 116, 22631-22636.
image

Abstract

We report the conformational restriction of a freely rotating biaryl derivative resulting in strong exciton coupled circular dichroism between the two nondegenerate fragments of the dyad NP only in the presence of DNA. The napthalenimide–perylenimide dyad NP, an extended 1,1′-binaphthalene derivative, has a rotational barrier of 100 kJ/mol, leading to fast racemization. While end-stacking with a DNA hairpin, NP exhibits a significantly high rotational barrier, an additional 91 kJ/mol, resulting in atroposelective preference. Such reversible conformational constraints using biotemplates show huge potential toward conformational analysis, dynamic kinetic resolution, and asymmetric synthesis. The present work focuses on conformational analysis of a freely rotating biaryl derivative using a combination of techniques such as temperature-dependent UV–vis, circular dichroism, steady-state and time-resolved fluorescence spectroscopy, and molecular dynamics simulation.

27)  Effect of Temperature on Symmetry Breaking Excited State Charge Separation: Restoration of Symmetry at Elevated Temperature

H. Khandelwal, A. R. Mallia, R. T. Cheriya and M. Hariharan*
Journal PaperPhys. Chem. Chem. Phys., 2012, 15282-15285.
image

Abstract

With an increase in temperature, an unprecedented restoration of symmetry in the symmetry breaking excited state charge transfer is observed in a geminal pair of near-orthogonally connected perylenimide dimers. Such restoration of symmetry could be attributed to the interchromophoric planarization and/or loss of solvation asymmetry at elevated temperature resulting in enhanced fluorescence quantum yield.

26)  Energy Transfer in Near-Orthogonally Arranged Chromophores Separated through a Single Bond

R. T. Cheriya, J. Joy, A. P. Alex, A. Shaji, and M. Hariharan*
Journal PaperJ. Phys. Chem. C, 2012, 116, 12489–12498.
image

Abstract

A combined experimental and theoretical study shows a significant barrier (ca. 100 kJ/mol) to rotation through the interchromophoric carbon–carbon single covalent (1.49 Å) bond between the naphthalenimide and perylenimide units that prevents coplanarization of the two units in the dyad NP, thereby forcing them to act as independent chromophores/redox centers. Upon photoexcitation, highly efficient energy transfer is observed from the naphthalenimide (energy donor) to the perylenimide (energy acceptor) moiety predominantly through Coulombic coupling, completely isolating the orbital overlap (Dexter-type) interaction between the chromophoric units at such short separation by virtue of their orthogonal arrangement. Because Förster’s ideal-dipole approximation ignores the contribution from significant higher-order Coulombic interactions at such short distances between donor and acceptor moieties, the complete coupling was computed from the transition densities, giving an estimate of the energy-transfer rate from the naphthalenimide donor to the perylenimide acceptor of kET = 2.2 × 1010 s–1, in agreement with observations. Ultrafast excitation energy (ca. 40 ps, 90%) and electron (<0.5 ps, 10%) transfer from the singlet excited state of naphthalenimide to the perylenimide moiety competes with further delayed processes in the conjugate NP. Upon excitation at 345 nm, conjugate NP exhibits near-quantitative energy transfer in conjunction with solvent-polarity-dependent (solvatochromic) perylenimide fluorescence, resulting in a remarkable Stoke’s shift of ca. 175–240 nm. Favorable photophysical properties such as high fluorescence quantum yield, wide excitation range, ultrafast energy transfer, marginal electron transfer, and large Stoke’s shift make this conjugate a potential candidate for biological applications.

25)  Facially-Selective Thymine-Thymine Photodimerization in TTT Triads

P. P. Neelakandan, Z. Pan, M. Hariharan and F. D. Lewis*
Journal PaperPhotochem. Photobiol. Sci., 2012, 11, 889-892.
image

Abstract

Irradiation of alkane-linked DNA hairpins possessing TTT steps with flanking purine bases yields products identified as the cis–syn (2 + 2) dimers formed between the central thymine and its 3′- and 5′-neighbors. Selective formation of the 3′-dimer is attributed to ground state conformational effects and electron transfer quenching by purine bases.

2011

24)  Electron Donor–Acceptor Interactions with Flanking Purines Influence the Efficiency of Thymine Photodimerization

Z. Pan, M. Hariharan, J. D. Arkin, A. S. Jalilov, M. McCullagh, G. C. Schatz, and F. D. Lewis*
Journal PaperJ. Am. Chem. Soc. 2011, 133, 20793–20798.
image

Abstract

Quantum yields for thymine photodimerization (ΦTT) have been determined for a series of short DNA single-strand and base-paired hairpin structures possessing a single thymine–thymine step with flanking purines. Values of ΦTT are strongly dependent upon the oxidation potential of the flanking purine, decreasing in the order: inosine > adenine > guanine > deazaguanine. The dependence of ΦTT on the ionization potential of the flanking purine is more pronounced when the purine of lower oxidation potential is located at the 5′- versus 3′-position in either a single strand or a hairpin. Molecular dynamics simulations for hairpin structures indicate that the TT step is π-stacked with both the 5′ and 3′ purine, but that there is little π-stacking with either purine in single-strand structures. The observation of moderately intense long-wavelength UV absorption features for hairpins having 5′-Z or G flanking purines suggests that excitation of ground state donor–acceptor complexes may account for more extensive quenching of dimerization by 5′- versus 3′-purines. The “purine effect” on ΦTT is attributed to a combination of ground state conformation, ground state electron donor–acceptor interactions, and excited state exciplex formation.

23)  Conformation of a Dodecane DNA Hairpin Linker. Multiple Gauche Bonds Cover the Bases

K. Siegmund, M. Hariharan, and F. D. Lewis*
Journal PaperJ. Phys. Chem. B, 2011, 115, 3740–3746.
image

Abstract

Alkane linkers derived from α,ω-alkane diols have been employed for the preparation of DNA mini-hairpins, which are suitable for studies of the spectroscopy and photochemistry of short base pair domains. The solution structure of a DNA hairpin having a n-dodecane linker and six AT base pairs has been determined using 1H NMR data with restrained molecular dynamics. The chemical shifts of the 12 diastereotopic pairs of linker protons show a distribution of values depending on their locations within the shielding region of the ring-currents of the adjacent base pair. Chemical shifts calculated from the mean NMR solution structure show the same overall distribution, but with larger absolute values for the upfield shifts. The C12 linker lies approximately parallel to the adjacent base pair and adopts a highly curved structure having an average of 4−5 gauche C−C bonds, in contrast to a modeled B-DNA structure which has a more fully extended alkane chain. This curved structure results in an average P−P distance of 15.4 Å, substantially shorter than the 17.7 Å average distance for B-DNA. This structure appears to maximize the hydrophobic interactions between the linker and the adjacent base pair. Partial NMR assignments for the C12 linker in a second hairpin having a different base-pair sequence indicates that it adopts a similar curved geometry having multiple gauche bonds. The hairpin base pair domain adopts a B-DNA geometry in which the AT base pair adjacent to the linker displays Watson−Crick base pairing, in spite of the relatively short P−P distance. The terminal bases-pair shows evidence of extensive end-fraying. The four interior base pairs display a normal B-DNA geometry, thus providing good models for base pair domains embedded in longer duplexes.

2010

22)  Hydrophobic Self-Assembly of a Perylenediimide-Linked DNA Dumbbell into Supramolecular Polymers

P. Neelakandan, Z. Pan, M. Hariharan, Y. Zheng, F. D. Lewis*, H. Weissman, and B. Rybtchinski*
Journal PaperJ. Am. Chem. Soc. 2010, 132, 15808-15813.
image

Abstract

The self-assembly of DNA dumbbell conjugates possessing hydrophobic perylenediimide (PDI) linkers separated by an eight-base pair A-tract has been investigated. Cryo-TEM images obtained from dilute solutions of the dumbbell in aqueous buffer containing 100 mM NaCl show the presence of structures corresponding to linear end-to-end assemblies of 10−30 dumbbell monomers. The formation of assemblies of this size is consistent with analysis of the UV−vis and fluorescence spectra of these solutions for the content of PDI monomer and dimer chromophores. Assembly size is dependent upon the concentration of dumbbell and salt as well as the temperature. Kinetic analysis of the assembly process by means of salt-jump stopped-flow measurements shows that it occurs by a salt-triggered isodesmic mechanism in which the rate constants for association and dissociation in 100 mM NaCl are 3.2 × 107 M−1s−1 and 1.0 s−1, respectively, faster than the typical rate constants for DNA hybridization. TEM and AFM images of samples deposited from solutions having higher concentrations of dumbbell and NaCl display branched assemblies with linear regions >1 μm in length and diameters indicative of the formation of small bundles of dumbbell end-to-end assemblies. These observations provide the first example of the use of hydrophobic association for the assembly of small DNA duplex conjugates into supramolecular polymers and larger branched aggregates.

21)  Conformational Control of Thymine Photodimerization in Single-Strand and Duplex DNA Containing Locked Nucleic Acid TT Steps

M. Hariharan, M. McCullagh, G. C. Schatz, and F. D. Lewis*
Journal PaperJ. Am. Chem. Soc. 2010, 132, 12856-12858.
image

Abstract

The results of an integrated experimental and theoretical study of thymine−thymine photodimerization in short single-strand and duplex DNA structures possessing a single locked nucleic acid TT step are reported. Control of ground-state conformation by the locked nucleic acids results in a marked increase in both the quantum yield and the selectivity of photoproduct formation.

20)  Structure and Stability of Alkane-Linked DNA Hairpin Conjugates

M. Hariharan,* K. Siegmund, and F. D. Lewis*
Journal PaperJ. Org. Chem. 2010, 75, 6236–6243.
image

Abstract

The synthesis and properties of three related families of alkane-linked DNA hairpins are reported. The first possesses a dodecane linker (C12) and 2−8 AT base pairs. The second possesses six AT base pairs and straight chain alkane linkers having 8−16 methylenes. The third has three alkane linkers of different length and a constant six base-pair stem with alternating A-T bases and a single TT step. The spectroscopic properties (UV, CD, and 1H NMR) and molecular modeling are consistent with the formation of base-paired B-DNA structures for all hairpins having four or more AT base pairs. The thermal stability of hairpins having a C12 linker is greater than that of the commonly used hexa(ethylene glycol) linker but less than that of the stilbenediether linker having the same AT base-pair domain. Hairpin stability is related to both hydrophobic interactions between the linker and the adjacent base pair (stilbene > alkane > glycol) and the overall length of the linker. The stability of the alkane-linked hairpins having six AT base pairs is greater for a tetradecane linker than for either shorter or longer linkers. The good thermal stability of alkane-linked hairpins and absence of a chromophore which absorbs in the UV region makes them well-suited for studies of the electronic spectra and photochemistry of short hairpins having variable base-pair sequences.

19)  Perylenediimide-Linked DNA Dumbbells: Long-Distance Electronic Interactions and Hydrophobic Assistance of Base-Pair Melting

M. Hariharan, K. Siegmund, Y. Zheng, H. Long, G. C. Schatz, and F. D. Lewis*
Journal PaperJ. Phys. Chem. C 2010, 114, 20466–20471.
image

Abstract

The synthesis and properties of synthetic DNA dumbbells having A-tract base pair domains consisting of 6−16 base pairs connected by perylenediimide (PDI) linkers are reported. The dumbbells were prepared in good yield by chemical ligation of nicked-dumbbell precursors having six or more A-T base pairs. The dumbbell structures have been investigated by a combination of electronic spectroscopy and molecular dynamics simulations. UV−visible spectra are indicative of the formation of monomeric dumbbells at room temperature in aqueous buffer in the absence of added salt. The long-wavelength region of the circular dichroism (CD) spectra is a composite of induced CD of the PDI monomers and intramolecular exciton-coupled CD between the two PDI chromophores. Weak exciton coupled CD can be observed between PDI chromophores separated by 13 base pairs, thus extending the reach of dumbbell molecular rulers. Upon heating, the dumbbells undergo base pair melting and intramolecular PDI−PDI association. Analysis of the temperature-dependent spectral data provides evidence for a three-state model in which base pair melting of the intact dumbbell results in the formation of an intermediate species which is in equilibrium with a collapsed dumbbell having intramolecular PDI−PDI stacking. The low melting temperatures of the shorter dumbbells are attributed to the partial compensation of PDI−PDI association for base pair dissociation.

18)  DNA Base-Pair Flipping with Fluorescent Perylenediimide Pincers

T. A. Zeidan, M. Hariharan, K. Siegmund, and F. D. Lewis*
Journal PaperPhotochem. Photobiol. Sci. 2010, 9, 916-922.
image

Abstract

The synthesis, structure, and electronic spectra of a series of DNA hairpins possessing two perylenediimide (PDI) base pair surrogates are reported. The PDI chromophores are located in opposite strands of the hairpin base pair domain opposite abasic sites and are either adjacent to each other or separated by a variable number of AT or GC base pairs. Molecular modeling of the conjugate having adjacent PDI chromophores shows that they adopt a slipped, π-stacked geometry with an angle of 40° between the PDI long axes. The electronic absorption, fluorescence, and circular dichroism of this conjugate are consistent with a stacked PDI structure. Conjugates having one or two GC base pairs between the PDI chromophores display spectra that are consistent with isolated PDIs. Conjugates having 1–4 AT base pairs have more complex spectra, suggestive of an equilibrium between base paired and flipped structures having stacked PDIs. Heating of the conjugates possessing isolated PDI chromophores results in base pair flipping. The free energy for PDI stacking is greater than that for a single AT base pair and comparable to that for a single GC base pair or two AT base pairs.

17)  Conformational Control of TT-Dimerization in DNA Hairpins. A Molecular Dynamics Study

M. McCullagh, M. Hariharan, F. D. Lewis*, D. Markovitsi, T. Douki and G. C. Schatz*
Journal PaperJ. Phys. Chem. B 2010, 114, 5215-5221.
image

Abstract

The paper presents quantum yield results for the [2+2] and 6-4 photodimerization of TT steps in several DNA structures, including hairpins where the context dependence of the photodimerization yield is determined, and it develops a theoretical model that correctly describes the trends in dimerization yield with DNA structure. The DNA conjugates considered include dT20, dA20dT20, and three alkane-linked hairpins that contain a single TT step. The theoretical modeling of the [2+2] process is based on CASSCF electronic structure calculations for ethylene + ethylene, which show that photoexcitation of low-lying excited states leads to potential surfaces that correlate without significant barriers to a conical intersection with the ground state surface at geometries close to the dimer structure. The primary constraint on dimerization is the distance d between the two double bonds, and it is found that d < 3.52 Å leads to quantum yield trends that match the observed trends within a factor of 3. Constraints on the dihedral angle between the two double bonds are not as important, and although it is possible to generate better dimerization yield predictions for some structures by including these constraints, the best overall picture is obtained with no constraint. For 6-4 dimerization, a distance g < 2.87 Å and no constraint on dihedral angle provide an accurate description of the yield.

16)  Site-selective Interactions: Squaraine Dye-Serum Albumin Complexes with Enhanced Fluorescence and Triplet Yields

V. S. Jisha, K. T. Arun, M. Hariharan and D. Ramaiah*
Journal PaperJ. Phys. Chem. B 2010, 114, 5912-5919.
image

Abstract

We report the effect of steric factors of a few squaraine dyes, bis(2,4,6-trihydroxyphenyl)squaraine (1), bis(3,5-dibromo-2,4,6-trihydroxyphenyl)squaraine (2), and bis(3,5-diiodo-2,4,6-trihydroxyphenyl) squaraine (3), on their binding with human (HSA) and bovine (BSA) serum albumins employing photophysical, chiroptical, biophysical, and microscopic techniques. These dyes interact with serum albumins very efficiently and exhibit site selectivity, involving synergistic effects of hydrophobic, hydrogen bonding, and electrostatic interactions. The association constants of these complexes have been determined and are found to be 4.9 × 106 and 4.1 × 105 M−1, respectively, for the dyes 2 and 3 with BSA, while HSA showed relatively higher association constants of 6.0 × 106 and 9.9 × 105 M−1. Highly clear distinction in site-selective binding can be ascertained from time-resolved fluorescence, displacement cum fluorimetry, and circular dichroism (CD) studies. The increased affinity toward the major binding site (site II, domain III) over the relatively smaller binding site (site I, domain II) in the serum albumin with the increasing size of the heavy atoms present in 2 and 3 as compared to 1 indicates the importance of steric factors thereby confirming that the dye structure has a predominant role in deciding site selectivity. The distance between the energy donor and acceptor was calculated using Förster theory, which agrees well with the reported site 1 binding agent dansylamine. In contrast, no energy transfer was observed between tryptophan (Trp-214) present in domain II of the albumins and the dyes 2 and 3, indicating that these derivatives bind less efficiently at site I due to steric conatraints but preferentially bind at site II. Laser flash photolysis studies of the dyes 2 and 3 in the presence of HSA exhibited ca. 2.5-fold enhancements in the triplet lifetimes and quantum yields when compared to that obtained in buffer. The uniqueness of these dyes is that they show substituent size-dependent selectivity at site II of serum albumins and signal the event through “turn on” fluorescence intensity as well as enhanced triplet excited state lifetimes and quantum yields, thereby indicating their potential use as NIR noncovalent protein labeling and photodynamic therapeutic agents.

15)  Electron Hopping among Cofacially Stacked Perylenediimides Assembled Using DNA Hairpins

T. M. Wilson, T. A. Zeidan, M. Hariharan, F. D. Lewis*, and M. R. Wasielewski*
Journal PaperAngew. Chem. 2010, 49, 2385-2388.
image

Abstract

Charge on through: Perylenediimide chromophores incorporated into DNA hairpins serve as base-pair surrogates and form a zipperlike intercalated structure (see picture). Electron hopping was observed within the chromophore stacks upon one-electron reduction.

14)  Direct Evidence on the External Stimuli Induced Dissembly of DNA through Microscopic Techniques

M. Hariharan, E. Kuruvilla and D. Ramaiah*
Journal PaperJ. Phys. Chem. Lett. 2010, 1, 834-838.
image

Abstract

Calf thymus DNA exhibited a regular network-like structure on mica and copper surfaces, respectively, under atomic force (AFM) and scanning electron (SEM) microscopic techniques while oily streak cholesteric birefringent texture was observed on the glass surface under optical polarizing microscopy (OPM). In the presence of an external stimuli such as temperature, intercalating compounds such as the viologen-linked pyrene 1 and para-tolylacridinium iodide (2) and the minor groove binding spermine (4) prevented the DNA−DNA interactions and thereby perturbed the self-assembly of DNA. In contrast, the major groove binding bovine serum albumin (BSA) and the noninteracting ligand ortho-tolylacridinium iodide (3) did not affect the overall morphology of DNA, as characterized through the AFM, SEM, OPM, and circular dichroism (CD) techniques. As far as we know, this is the first report that presents direct evidence for the perturbation of supramolecular assembly of DNA under various conditions and that can be visualized through different microscopic techniques.

13)  Photoinduced DNA Damage Efficiency and Cytotoxicity of Novel Viologen Linked Pyrene Conjugates

M. Hariharan, D. Ramaiah*, I. Schulz, S. C. Karunakaran and B. Epe
Journal PaperChem. Comm. 2010, 46, 2064-2066.
image

Abstract

Novel viologen linked pyrene conjugates permeate cells efficiently and exhibit spacer length dependent DNA damage and cytotoxicity upon photoexcitation.

2009

12)  Hydrophobic Dimerization and Thermal Dissociation of Perylenediimide-Linked DNA Hairpins

M. Hariharan, Y. Zheng, H. Long, T. A. Zeidan, G. C. Schatz, J. Vura-Weis, M. R. Wasielewski, X. Zuo, D. M. Tiede, and F.. D. Lewis*
Journal PaperJ. Am. Chem. Soc. 2009, 131, 5920-5929.
image

Abstract

The structure and properties of hairpin-forming bis(oligonucleotide) conjugates possessing perylenediimide (PDI) chromophores as hairpin linkers have been investigated using a combination of spectroscopic and computational methods. These conjugates exist predominantly as monomer hairpins at room temperature in the absence of added salt and as head-to-head hairpin dimers in the presence of >50 mM NaCl. The hairpin dimer structure is consistent with the results of small-angle X-ray scattering in aqueous solution and molecular dynamics simulation. The structure of the nonconjugated PDI dimer in water is investigated using potential of mean force calculations. The salt dependence is attributed to increased cation condensation in the hairpin dimer vs monomer. Upon heating at low salt concentrations, the hairpin dimer undergoes sequential dissociation to form the monomer hairpin followed by conversion to a random coil structure; whereas at high salt concentrations both dissociation processes occur over the same temperature range. The monomer and dimer hairpins have distinct spectroscopic properties both in the ground state and excited singlet state. The UV and CD spectra provide evidence for electronic interaction between PDI and the adjacent base pair. Low fluorescence quantum yields are observed for both the monomer and dimer. The transient absorption spectrum of the dimer undergoes time-dependent spectral changes attributed to a change in the PDI−PDI torsional angle from ca. 20° in the Franck−Condon singlet state to ca. 0° in the relaxed singlet state, a process which occurs within ca. 40 ps.

11)  Sum rules and determination of exciton coupling using absorption and circular dichroism spectra of biological polymers

A. Burin, M. Armbruster, M. Hariharan and F. D. Lewis*
Journal PaperProc. Natl. Acad. Sci. USA 2009, 106, 989-984.
image

Abstract

Optical spectra of biological polymers contain important information about their structure and function in living organisms. This information can be accessed by extracting an optical interaction of monomers, i.e., their exciton coupling, from experimental data. This coupling is sensitive to molecular structure, geometry, and conformation and can be used to characterize them. However, the accurate determination of exciton coupling in important biological molecules is difficult because inhomogeneous broadening smears out the monomer interaction. We suggest a way to overcome this problem by applying exact sum rules. These sum rules are derived by establishing a straightforward relationship between integral characteristics of absorption and circular dicroism spectra, and exciton coupling. Exciton coupling between AT pairs in native DNA conformation is estimated by applying these sum rules to DNA hairpin optical spectra as V0 ∼ 0.035 eV in agreement with the earlier numerical calculations.

2008

10)  Photoinduced Charge Separation in Pyrenedicarboxamide-linked DNA Hairpins

P. Daublain, K. Siegmund, M. Hariharan, J. Vura-Weis, M. R. Wasielewski, F. D. Lewis*, V. Shafirovich*, Q. Wang, M. Raytchev, and Torsten Fiebig*
Journal PaperPhotochem. Photobiol. Sci. 2008, 7, 1501-1508.
image

Abstract

The structure and properties of hairpin-forming bis(oligonucleotide) conjugates possessing perylenediimide (PDI) chromophores as hairpin linkers have been investigated using a combination of spectroscopic and computational methods. These conjugates exist predominantly as monomer hairpins at room temperature in the absence of added salt and as head-to-head hairpin dimers in the presence of >50 mM NaCl. The hairpin dimer structure is consistent with the results of small-angle X-ray scattering in aqueous solution and molecular dynamics simulation. The structure of the nonconjugated PDI dimer in water is investigated using potential of mean force calculations. The salt dependence is attributed to increased cation condensation in the hairpin dimer vs monomer. Upon heating at low salt concentrations, the hairpin dimer undergoes sequential dissociation to form the monomer hairpin followed by conversion to a random coil structure; whereas at high salt concentrations both dissociation processes occur over the same temperature range. The monomer and dimer hairpins have distinct spectroscopic properties both in the ground state and excited singlet state. The UV and CD spectra provide evidence for electronic interaction between PDI and the adjacent base pair. Low fluorescence quantum yields are observed for both the monomer and dimer. The transient absorption spectrum of the dimer undergoes time-dependent spectral changes attributed to a change in the PDI−PDI torsional angle from ca. 20° in the Franck−Condon singlet state to ca. 0° in the relaxed singlet state, a process which occurs within ca. 40 ps.

9)  Context-Dependent Photodimerization in Isolated Thymine-Thymine Steps in DNA

M. Hariharan and F. D. Lewis*
Journal PaperJ. Am. Chem. Soc. 2008, 130, 11870-11871.
image

Abstract

The effect of 280 nm irradiation on a family of synthetic DNA hairpins possessing an alkane linker connecting a six-base pair stem having a single T−T step located at different positions within the hairpin has been investigated. A single adduct assigned to the product of 2+2 dimerization is obtained except in the case of a T−T step located adjacent to the linker, in which case both 2+2 and 6−4 adducts are obtained. The efficiency of dimerization is similar for three hairpins having a T−T step located within the duplex interior. Lower efficiency is observed for a T−T step located at the open end of the hairpin and in T overhangs, whereas higher efficiency is observed for the T−T step adjacent to the linker and in a single T bulge. The context-dependence of dimerization efficiency is discussed.

2007

8)  Encapsulation of Electron Donor-Acceptor Dyads in b-Cyclodextrin Cavity: Unusual Planarization and Enhancement in Rate of Electron Transfer Reaction

M. Hariharan, P. P. Neelakandan and D. Ramaiah*
Journal PaperJ. Phys. Chem. B, 2007, 111, 11940-11947.
image

Abstract

Interaction of β-cyclodextrin (β-CD) with a few novel electron donor acceptor dyads 1a−c and 2a−c, having aryl and flexible methylene spacer groups, has been investigated through photophysical, chiroptical, electrochemical, NMR, and microscopic techniques. Dyads 1a and 1c, with p-tolyl and biphenyl spacer groups, respectively, exhibited significantly decreased fluorescence quantum yields and lifetimes in the presence of β-CD, while negligible changes were observed for dyad 1b with an o-tolyl spacer. In contrast, spacer-length-dependent significant enhancement in fluorescence quantum yields and lifetimes was observed for dyads 2a−c, with flexible polymethylene (n = 1, 3, 11) spacer groups. Association constants of β-CD encapsulated complexes have been determined and the contrast behavior observed in these systems is explained through an electron transfer (kET) mechanism based on calculated favorable change in free energy (ΔGET = −1.27 eV) and the redox species characterized through laser flash photolysis studies. Rates of kET have been estimated and are found to increase ca. 2-fold in the case of dyads 1a and 1c when encapsulated in β-CD, while significantly decreased kET values were observed for the dyads 2a−c with flexible spacer (ca. 9-fold for 2c). As characterized through cyclic voltammetry, 2D NMR [correlated (COSY) and nuclear Overhauser enhancement (NOESY) spectroscopy], and laser flash photolysis studies, the β-CD encapsulation of dyads with aliphatic spacer groups leads to the conformational unfolding of a sandwich type of structure, whereas dyads with rigid aryl spacer groups undergo unusual planarization as compared to the uncomplexed dyads, resulting in enhanced electron-transfer reaction between the donor and acceptor moieties.

7)  Chiral supramolecular assemblies of a squaraine dye in solution and thin films: concentration-, temperature-, and solvent-induced chirality inversion

K. Jyothish, M. Hariharan and D. Ramaiah*
Journal PaperChem. Eur. J. 2007, 13, 5944-5951.
image

Abstract

We prepared novel cholesterol-appended squaraine dye 1 and model squaraine dye 2 and investigated their aggregation behavior in solution and thin films using photophysical, chiroptical, and microscopic techniques. Investigations on the dependence of aggregation on solvent composition (good/poor, CHCl3/CH3CN) demonstrated that squaraine dye 1 forms two novel H-type chiral supramolecular assemblies with opposite chirality at different good/poor solvent compositions. Model compound 2 formed J-type achiral assemblies under similar conditions. The supramolecular assembly of 1 observed at lower fractions of the poor solvent could be assigned to the thermodynamically stable form, while a kinetically controlled assembly is formed at higher fractions of the poor solvent. This assignment is evidenced by temperature- and concentration-dependent experiments. With increasing temperature, the chirality of the kinetically controlled aggregate was lost and, on cooling, the aggregate with the opposite chirality was formed. On further heating and cooling the aggregates thus formed resulted in no significant changes in chirality, that is they are thermodynamically stable. Similarly, at lower concentrations, the thermodynamically stable form exists, but at higher concentration aggregation was found to proceed with kinetic control. Based on these observations it can be assumed that formation of the kinetically controlled assembly might be largely dependent on the presence of the nonpolar cholesterol moiety as well as the amount of poor solvent present. However, under solvent-free conditions, structurally different aggregates were observed when drop cast from solutions containing monomer, whereas a left-handed CD signal corresponding to the thermodynamically controlled assemblies was observed from pre-aggregated solutions.

6)  Selective Recognition of Tryptophan through the Inhibition of Intramolecular Charge-Transfer Interactions in an Aqueous Medium

M. Hariharan, C. K. Suneesh and D. Ramaiah*
Journal PaperOrg. Lett. 2007, 9, 417-420.
image

Abstract

A novel donor−acceptor conjugate 1 was synthesized, and its interactions with various amino acids have been investigated as compared to the model system 2. The conjugate 1 unusually forms an intramolecular charge-transfer complex in the aqueous medium and undergoes selective binding interactions with tryptophan. The uniqueness of this system is that it selectively recognizes tryptophan among all other amino acids and involves synergistic effects of π-stacking, electrostatic, and donor−acceptor interactions.

2006

5)  Novel Bifunctional Viologen-Linked Pyrene Conjugates: Synthesis and Study of their Interactions with Nucleosides and DNA

M. Hariharan, J. Joseph and D. Ramaiah*
Journal PaperJ. Phys. Chem. B 2006, 110, 24678-24686.
image

Abstract

With the objective of developing efficient DNA oxidizing agents, a new series of viologen-linked pyrene conjugates with the general formula PYLnV2+, having a different number of methylene spacer units (Ln) was synthesized, and their interactions with nucleosides and DNA have been investigated through photophysical and biophysical techniques. The viologen-linked pyrene derivatives PYL1V2+ (n = 1), PYL7V2+ (n = 7), and PYL12V2+ (n = 12) exhibited characteristic fluorescence emission of the pyrene chromophore centered around 380 nm but with significantly reduced yields when compared to those of the model compound PYL1Et3+. The fluorescence quenching observed in these systems is explained through an electron-transfer mechanism based on a calculated favorable change in free energy (ΔGET = −1.59 eV), and the redox species characterized through laser flash photolysis studies. Intramolecular electron-transfer rate constants (kET) were calculated from the observed fluorescence yields, and the singlet lifetimes of the model compound and are found to decrease with increasing spacer length. The DNA binding studies of these systems through photophysical, chiroptical, and viscometric techniques demonstrated that these systems effectively undergo DNA intercalation with association constants (KDNA) in the range of 1.1−2.6 × 104 M-1 and exhibit 2:1 sequence selectivity for poly(dG)·poly(dC) over poly(dA)·poly(dT). Photoactivation of these systems initiates electron transfer from the singlet excited state of the pyrene chromophore to the viologen moiety followed by an electron transfer from DNA to the oxidized pyrene. This results in the formation of stable charge-separated species such as radical cations of both DNA and reduced viologen as characterized by laser flash photolysis studies and subsequently the oxidized DNA modifications. These novel systems are soluble in buffer media, stable under irradiation conditions, and oxidize DNA efficiently and selectively through a cosensitization mechanism and hence can be useful as photoactivated DNA cleaving agents.

4)  A Supramolecular ON-OFF-ON Fluorescence Assay for Selective Recognition of GTP

P. P. Neelakandan, M. Hariharan and D. Ramaiah*
Journal PaperJ. Am. Chem. Soc. 2006, 128, 11334-11335.
image

Abstract

With the objective of developing small molecule based receptors for nucleosides and nucleotides, interactions of a cyclic donor−acceptor conjugate 1 with adenosine, AMP, ADP, CTP, UTP, ITP, ATP, and GTP have been investigated by absorption, steady-state, and time-resolved fluorescence, cyclic voltammetry (CV), NMR, and fluorescence indicator displacement techniques. Titration of 1 with the fluorescent indicator, 8-hydroxy-1,3,6-pyrene trisulfonate (HPTS), resulted in nearly complete fluorescence quenching of HPTS, along with 25% hypochromicity in its absorption spectrum. Benesi−Hildebrand analysis gave a 1:1 stoichiometry for the complex between the receptor 1 and HPTS with an association constant (Kass) of 4.66 × 104 M-1 in buffer. The driving force for such a complexation was evaluated to be the synergistic effects of π-stacking and electrostatic interactions inside the cavity as confirmed by the effect of ionic strength, temperature, and the negative results obtained with the model compound 2. Titration of the nonfluorescent complex [1·HPTS] with various nucleosides and nucleotides resulted in revival of fluorescence of the indicator, HPTS. It was observed that GTP induces maximum displacement of HPTS from the complex [1·HPTS] with an overall fluorescence enhancement of ca. 150-fold. The addition of adenosine, AMP, ADP, CTP, and UTP showed negligible changes, whereas ca. 45- and 50-fold enhancement was observed with ATP and ITP, respectively. The competitive displacement of the indicator by various analytes is found to be in the order GTP (buffer) ≈ GTP (biofluid) ≫ ITP ≈ ATP > UTP > CTP ≈ ADP ≈ AMP ≈ Ade. By virtue of having a better π-electron cloud, GTP undergoes effective electronic, π-stacking, and electrostatic interactions inside the cavity and forms a stable complex with the receptor 1. The uniqueness of this assay is that it differentiates GTP from ATP and other nucleotides and signals the event through a visual “turn on” fluorescence mechanism in buffer as well as in biological fluids.

3)  Site-Selective Binding and Dual Mode Recognition of Serum Albumin by a Squaraine Dye

V. S. Jisha, K. T. Arun, M. Hariharan and D. Ramaiah*
Journal PaperJ. Am. Chem. Soc. 2006, 128, 6024-6025.
image

Abstract

With the objective of developing small molecule based probes for proteins, interactions of polyhydroxyl-substituted squaraine dye (SQ) with bovine serum albumin (BSA) have been investigated by absorption, steady-state and time-resolved fluorescence, circular dichroism (CD), cyclic voltammetry (CV), 1H NMR, scanning electron, and tapping mode atomic force microscopic techniques. Increase in addition of BSA resulted in increase in absorbance and fluorescence quantum yields (80-fold) of SQ, along with significant bathochromic shifts in the absorption and fluorescence maxima. Half-reciprocal analysis of the absorption data gave a 1:1 stoichiometry for the complex between BSA and SQ with high association (Kass) constant of (1.4 ± 0.1) × 106 M-1 and change in free energy of −35 kJ/mol. The complex formation was further confirmed by observation of induced CD signal corresponding to the SQ chromophore at 610 nm, upfield shift (about Δδ 0.1 ppm) of aromatic protons of SQ in 1H NMR spectra, and decrease in current intensity (CV) of SQ when bound to BSA. The picosecond time-resolved fluorescence studies indicated that the BSA−SQ complex exhibits biexponential decay with significantly enhanced lifetimes of 0.5 and 1.5 ns when compared to the lifetime of SQ (τ = 121 ps) in the absence of BSA. Employing displacement cum fluorimetry using site-specific binding ligands, such as dansylproline and dansylamide, indicated that SQ binds with protein selectively at site II involving hydrophobic, hydrogen bonding, and electrostatic interactions. The uniqueness of this molecular system is that it interacts with BSA selectively at site II and signals the binding event through dual mode recognition of “visual color” change and “turn on” fluorescence mechanism.

2005

2)  Synthesis of a Novel Cyclic Donor-Acceptor Conjugate for Selective Recognition of ATP

P. P. Neelakandan, M. Hariharan and D. Ramaiah*
Journal PaperOrg. Lett. 2005, 5765-5768.
image

Abstract

Novel cyclophane 1 was synthesized, and its interactions with phosphate, adenosine, AMP, ADP, and ATP have been investigated. With addition of ATP, significant decrease in absorbance of 1 was observed, whereas other guest molecules showed negligible effect. The complex between 1 and ATP was confirmed through cyclic voltammetry and 1H NMR. The uniqueness of the system is that it complexes selectively with ATP in a cavity and involves synergistic effects of both electrostatic and π−π stacking interactions.

Patent

1)  A Novel Cyclic Donor- Acceptor Conjugate, Process and a Supramolecular Fluorescent Marker Thereof

D. Ramaiah, P. P. Neelakandan and M. Hariharan
PatentIN Patent No. 253901, dated August 31, 2012.

Current Members

  • image

    Abbey M. Phillip

    Ph.D. student 2013 - present

      abbey@iisertvm.ac.in

  • image

    Remya Ramakrishnan

    Ph.D. student 2016 - present

      remyaramakrishnan16@iisertvm.ac.in

  • image

    Ebin Sebastian

    Ph.D. student 2017 - present

      ebinsebastian17@iisertvm.ac.in

  • image

    Devika S.

    Integrated Ph.D. student 2015 - present

      1994devikas15@iisertvm.ac.in

  • image

    Athira T. John

    Ph.D. student 2017 - present

      athira17@iisertvm.ac.in

  • image

    Amalu Mohan M.

    Project Assistant 2016 - Present

      amalumohan7@gmail.com

  • image

    Lijina M. P.

    Integrated Ph.D. student 2016 - present

      lijinamp16@iisertvm.ac.in

  • image

    Amal K. Homer

    Project Assistant 2018 - Present

      amalkhomercherai13@iisertvm.ac.in

  • image

    Ambily R. V.

    BSMS Student

      rvambili199614@iisertvm.ac.in

  • image

    Hridya P.

    BSMS Student

      hridya1997premkalpetta14@iisertvm.ac.in

  • image

    Niyas M. A.

    BSMS Student

      niyasma014@iisertvm.ac.in

  • image

    Vishnu V.

    BSMS Student

      vishnuvijay9615@iisertvm.ac.in

  • image

    Alfy Benny

    BSMS Student

      alfy16@iisertvm.ac.in

Past Ph.D. Members

Ongoing Research Grants

  • image

    Nano Mission

    Department of Science and Technology Nano Mission

    Dipolar and Multipolar Interactions in Assembled Molecules and Nanostructures: Developing a General Description and its Applications, 01/06/2016-31/05/2019, Rs. 5,61,20,800. Collaborative grant for Prof. K. George Thomas, Dr. R. S. Swathi, Dr. Adithya Lakshmanna and myself.

  • image

    Indo-Italian Project

    Indo-Italian Executive Programme of Cooperation in Scientific and Technological Cooperation

    Charge and Energy Transfer in Molecular Multifunctional Materials, 16/11/2017-15/11/2019, Rs. 10,20,000/-. Indo-Italian Joint Project for Dr. Mahesh Hariharan, Prof. K. George Thomas and Dr. R. S. Swathi in collaboration with Prof. Anna Painelli from the University of Parma.

  • image

    KSCSTE

    Kerala State Council for Science Technology and Environment

    Design, synthesis and photocatalytic water splitting properties of functional cobalt based inorganic-organic hybrids, 26/10/2015-15/10/2018, Rs. 45,20,000.

Completed Research Grants

  • image

    Department of Biotechnology

    Department of Biotechnology

    Mechanistic Investigations on Light Induced Crosslinking of DNA Protein Nanostructures, 15/02/2013-14/02/2016, Rs. 53,76,000

  • image

    Department of Science and Technology

    Department of Science and Technology

    Synthesis, Structure and Electronic Properties of Natural and Non-Natural Nucleic Acid Sequences, 24/05/2012-13/05/2015, Rs. 26,08,000

Travel Grants

  • image

    Royal Society of Chemistry

    Royal Society of Chemistry, UK

    Awarded a travel grant of Rs. 1,00,000 (£ 1000) to attend ‘2nd International Conference on Clean Energy Science’ Qingdao, China, April 13-16, 2014.

  • image

    Young Science Scheme

    Kerala State Young Science Scheme

    Awarded a travel grant of Rs. 1,70,000 to attend ‘24th Winter I-APS Conference’ Florida, USA, January 1-4, 2015

  • image

    Indo-US Science and Technology Forum

    Indo-US Science and Technology Forum

    Awarded a fellowship/travel grant of Rs. 6,26,000 to visit Montana State University, USA, June 9-September 5 2014

  • image

    Indo-UK Scientific Seminar

    Royal Society UK and DST India

    Awarded a travel grant of Rs. 1,00,000 to attend ‘Indo-UK Scientific Seminar’, University of Leeds, UK, February 16-18, 2015

Theory Courses

  • CHY111
    Atomic Structure and Chemical Bonding
  • CHY211
    Chemical Reactions and Reactive Intermediates
  • CHY221
    Principles of Physical Chemistry
  • IDC221
    Principles and Applications of Spectroscopy
  • CHY314
    Instrumental Methods
  • CHY422
    Physical Organic Chemistry

Laboratory Courses

  • CHY212
    Chemistry Lab III
  • CHY222
    Chemistry Lab IV
  • CHY415
    Advanced Physical Chemistry Laboratory

Contact & Meet Mahesh



You can find Mahesh at his office located at Room No. 3112, Chemical Science Block,IISER Thiruvananthapuram. He is at his office every day from 9:00 am until 7:00 pm, but you may consider a call/email to fix an appointment.

  •    Dr. Mahesh Hariharan
          3112, Chemical Science Block
          IISER Thiruvananthapuram
          Marathumala P.O., Vithura
          Thiruvananthapuram 695551
          Kerala, India,
  •    office: +91-471-2778101
  •    lab: +91-471-2778102
  •    mahesh@iisertvm.ac.in

Our Location

News Archive

  • Aug 2018
    Mahesh gets featured in Chemistry A European Young Chemists Special Issue 2018
    This second edition of the Young Chemists Special Issue has been assembled to honor the recent participants of the European Young Chemist Award (EYCA), presented at the 2014 and 2016 EuCheMS Congresses and young and emerging scientists from all different fields of chemistry around the world. Read Now
  • June 2018
    A new PCCP on photoinduced ultrafast processes
    Our work on exploring the excited state dynamics of benzophenone analogues get accepted in PCCP. Read Now
  • June 2018
    Vinayak bags the best undergraduate researcher medal
    Vinayak Bhat, with a total of three publications, two poster awards and an oral presentation award at various conferences secures the best undergraduate researcher medal at the sixth convocation of IISER-TVM.
  • May 2018
    Niyas secures SERB international travel grant
    Mr. Niyas M.A., final year BS-MS student in School of Chemistry, IISER TVM has been granted SERB international travel support to attend PhotoIUPAC2018 at Ireland.
  • May 2018
    Mahesh delivers a talk at ICTP, Trieste
    Mahesh delivered a talk entitled “Modulation of Rate of Charge Recombination in DNA” at the ‘Conference on the Complex Interactions of Light and Biological Matter: Experiments meet Theory’, International Centre for Theoretical Physics, Trieste, Italy, May 21-25, 2018.
  • May 2018
    Mahesh attends UK-India Frontiers of Science Meeting, Royal Society, London
    Mahesh presented a poster entitled “Strategies to Reduce the Rate of Charge Recombination” at the ‘UK-India Frontiers of Science Meeting’, The Royal Society at Chiechley Hall, London, May 15-18, 2018.
  • Feb 2018
    Ajith is now a Marie Sklodowska-Curie Individual Fellow
    Our alumnus, Ajith secured Marie Sklodowska-Curie Individual Fellowship. He will be working with Prof. David Amabilino, School of Chemistry, University of Nottingham, United Kingdom in the area of self-assembly and Organic electronics.
  • Jan 2018
    Article published
    Work of Vinayak, Gopika and Nanditha on mobility calculations of TMS pentacene gets published in Chemistry European Journal Read Now
  • Jan 2018
    Vinayak gets a poster award
    Mr. Vinayak Bhat, final year BS-MS student in School of Chemistry, IISER-TVM has been awarded the best poster prize in the Faraday Discussion held at Thiruvananthapuram, Kerala, India on 11-13 January 2018. The prize sponsored by Royal Society of Chemistry consists of a certificate and a book voucher.
  • Jan 2018
    Paper accepted
    Hard work of Niyas, Remya and Vishnu finally pays off. Our computational paper on TTF-TCNQ accepted in Chemistry European Journal. Read Now
  • 2017
    Arun joins our group as Research Associate
    Arun comes from Tokyo Metropolitian University where he obtained his Ph.D. under the supervision of Prof. Haruo Inoue.
  • Oct 2017
    Vinayak secured best oral presentation award
    Mr. Vinayak Bhat, final year BS-MS student in School of Chemistry, IISER-TVM has achieved the best oral presentation award at the 13th JNC Research Conference on Chemistry of Materials held at Thiruvananthapuram, Kerala, India on 01-03 October 2017. The prize consists of a certificate and a cash award.
  • Oct 2017
    Devika's poster win a prize
    Ms. Devika S., Integrated Ph.D. student in Dr. Mahesh Hariharan’s group, School of Chemistry, IISER-TVM has been awarded the best poster prize in the 13th JNC Research Conference on Chemistry of Materials held at Thiruvananthapuram, Kerala, India on 01-03 October 2017. The prize consists of a certificate and a cash award.
  • Sept 2017
    Vinayak won a poster award
    Mr. Vinayak Bhat, final year BS-MS student in School of Chemistry, IISER-TVM has been awarded the best poster prize in the 8th East Asian Symposium on Functional Dyes and Advanced Materials and dyes held at CSIR-NIIST, Thiruvananthapuram, Kerala, India on 20-22 September 2017. The prize sponsored by ACS Omega consists of a certificate and a cash award.
  • Aug 2017
    Remya gets a poster prize
    Ms. Remya Ramakrishnan, graduate student in Dr. Mahesh Hariharan's group, School of Chemistry, IISER-TVM has been awarded the best poster prize in the 24th Congress and General Assembly of the International Union of Crystallography Hyderabad International Convention Centre 21-28 August 2017, Hyderabad, India. The prize sponsored by authors of "Crystal Engineering – A Textbook", for describing crystal engineering studies consist of a certificate and a copy of the book "Crystal Engineering – A Textbook".
  • Aug 2017
    Niyas selected for Drangons' Den
    Mr. Niyas M. A., an undergraduate student/researcher in Dr. Mahesh Hariharan’s research group, School of Chemistry, IISER Thiruvananthapuram had been shortlisted for the Dragons’ Den, a scientific project proposal competition organized as part of the 24th Congress and General Assembly of the International Union of Crystallography held at Hyderabad International Convention Centre, Hyderabad, India from 21-28 August 2017.
  • Aug 2017
    Abbey visiting the US
    Mr. Abbey M. Philip, graduate student in Dr. Mahesh Hariharan's group, School of Chemistry, IISER-TVM have been selected for the prestigious "Bhaskara Advanced Solar Energy (BASE) Fellowship Program" supported by the Department of Science and Technology, Govt. of India, and the Indo-U.S. Science and Technology Forum (IUSSTF) to visit the South Dakota State University, United States.
  • Aug 2017
    Remya gets bursary from DST
    Ms. Remya Ramakrishnan, graduate student in Dr. Mahesh Hariharan's group, School of Chemistry, IISER-TVM has been awarded a bursary from Department of Science and Technology funds to attend the 24th IUCr Congress and General Assembly, 21-28 August 2017, Hyderabad, India. The abstract entitled “Columnar/Lamellar Packing in Cocrystals of Arylbipyridines with Diiodoperfluorobenzene” submitted by Ms. Remya Ramakrishnan has been awarded poster presentation by the chairs of ‘MS-093: Halogen bonding in crystal engineering’ at the 24th Congress and General Assembly of the International Union of Crystallography (IUCr 2017).
  • Aug 2017
    Niyas gets bursary from DST
    Mr. Niyas M A, BS-MS student in Dr. Mahesh Hariharan's group, School of Chemistry, IISER-TVM has been awarded a bursary from Department of Science and Technology funds to attend the 24th IUCr Congress and General Assembly, 21-28 August 2017, Hyderabad, India. The abstract entitled “Crystalline triphenylamine substituted arenes: solid state packing and luminescence properties” submitted by Mr. Niyas M A has been awarded poster presentation by the chairs of ‘MS-122: Crystallography of materials for energy’ at the 24th Congress and General Assembly of the International Union of Crystallography (IUCr 2017).
  • Sept 2016
    Abbey gets a poster prize
    Mr. Abbey Philip, Ph.D. student in Dr. Mahesh Hariharan’s group, School of Chemistry, IISER-TVM has been awarded the best poster prize in the 12th JNC Research Conference on Chemistry of Materials held at Thiruvananthapuram, Kerala, India on 23-25 September 2016. The prize consists of a certificate and a cash award.
  • Jun 2016
    Kalaivanan awarded best poster
    Mr. Kalaivanan Nagarajan, graduate student in Dr. Mahesh Hariharan's group, School of Chemistry, IISER-TVM has received Best Poster Award for the poster presented entitled “Activation of Triplet Excited in Core-Twisted Perylenediimides” at Gordon Research Conference on “Electronic Processes in Organic Materials” held at Lucca (Barga), Italy June 5-10, 2016.
  • Jun 2016
    Kalaivanan gets grant to attend Gordan Conference
    Mr. Kalaivanan Nagarajan, Ph.D. Scholar, has received a financial grant from Science and Engineering Research Board (SERB) for presenting a poster entitled "Activation of Triplet Excited State in Core-Twisted Perylenediimides" in "Gordon Research Conference on Electronic Processes in Organic Materials" to be held in Renaissance Tuscany Il Ciocco in Lucca (Barga), Italy, June 05-10, 2016
  • Mar 2016
    Malhotra Weikfield Foundation Nanoscience Award to Ajith
    Mr. Ajith R. Mallia, Research Scholar, Student of Dr. Mahesh Hariharan, School of Chemistry has received "Malhotra Weikfield Foundation Nanoscience Award" from Malhotra Weikfield Foundation for Advanced Studies in Nano Science Technology for the Academic Year 2016-2017, during 8th Bangalore India Nano conference held at Hotel Lalit Ashok, Bangalore, March 03-05, 2016. The award carries a certificate and a cash prize of Rs. 50,000/-.
  • Nov 2015
    Ajith gets poster award
    Mr. Ajith R. Mallia, Ph.D. Scholar, has received Chemical Science Best Poster Award from Royal Society of Chemistry, UK for the poster presented entitled “Light harvesting vesicular donor–acceptor scaffold limits the rate of charge recombination in the presence of an electron donor” during ‘Challenges in Organic Materials and Supramolecular Chemistry, ISACS18’ held in Indian Institute of Science, Bangalore, November 19-21, 2015.
  • Jan 2015
    Shinaj gets financial grant from SERB
    Mr. Shinaj K. Rajagopal, Ph.D. Scholar, has awarded a financial grant from Science and Engineering Research Board (SERB) for presenting a poster entitled “Progressive Acylation of Pyrene Engineers Solid State Packing and Color via C-H•••H-C, C-H•••O and ?-? Interactions” in ‘24th Winter I-APS Conference’ held in Florida, USA, January 1-4, 2015.
  • Mar 2014
    Kalaivanan bags poster prize
    Mr. Kalaivanan Nagarajan, Ph.D. Scholar, has received an award for best oral and poster presentation entitled “Single-Component Organic Light-Harvesting Red Luminescent Crystal” in ‘Organic Devices: The Future Ahead (ODeFA-2014)’ held in Bhabha Atomic Research Center, Mumbai, March 3-6, 2014.
  • July 2013
    SERB grant to Rijo
    Mr. Rijo T. Cheriya, Ph.D. Scholar, has awarded a financial grant from Science and Engineering Research Board (SERB) for presenting a poster entitled “Conformational and Excited State Dynamics of Near-Orthogonal Donor-Acceptor Bichromophores” in ‘Photochemistry Gordon Research Conference’ held in Stonehill College, Easton, MA, July 14-19, 2013
  • Feb 2013
    Best oral presentation prized to Jimmy
    Mr. Jimmy Joy, BS-MS Student, has received an award for best oral presentation entitled “DNA-Enforced Conformational Restriction of an Atropisomer” in ‘Chennai Chemistry Conference 2013’ held in CSIR-CLRI, Chennai, February 8-10, 2013