Our interest lies in photo-excited systems. We employ a variety of light-based techniques to study the behaviour of molecular systems and materials in their electronically excited state, determine the identity of the short-lived transient species through their spectral and temporal characteristics and investigate the dynamics of the ultrafast events. Quite often, we also exploit the photo-response of molecular systems as a tool for probing unknown and complex environments. In this Colloquium, I wish to present a brief outline of our recent research activities and then discuss in somewhat greater detail what we have learnt about the room temperature ionic liquids from the fluorescence response of specifically chosen molecular systems in these media.
Over the years, we have been exploring covalent and noncovalent chemistry to create molecular functional materials using synthetic organic molecules as building blocks. In the case of aromatic p-systems, electronic properties such as fluorescence, charge carrier mobility and conductivity can be modulated as a consequence of self-assembly. For the past several years we have been learning to use fluorescent molecular building blocks to the creation of a variety of supramolecular polymers and architectures with diverse, size, shape and properties. Many of these molecular assemblies form organogels with intriguing reversible properties. Some of them are excellent donor scaffolds for energy transfer which allows tuning of the emission colors. The fluorescence of these materials is extremely sensitive to the surroundings and hence useful for sensing and imaging. We have developed several fluorescent molecules and dyes for sensing of analytes and imaging of biological samples. The fascinating chemistry of the two different aspects of our research with fluorescent molecules will be discussed.
1. S. S. Babu, V. K. Praveen, A. Ajayaghosh, Chem. Rev. 2014, 114, 1973.
2. K. P. Divya, S. Sreejith, A. Pichandi, Y. Kang, Q. Peng, S. K. Maji, Y.Tong, H.Yu, Y. Zhao, P. Ramamurthy, A. Ajayaghosh Chem. Sci. 2014, 5, 3469.
3. R. Thirumalai, R. D. Mukhopadyay, V. K. Praveen, A. Ajayaghosh, Sci. Rep. 2015 DOI: 10.1038/srep09842.
4. P. Anees, S. Sreejith, A. Ajayaghosh, J. Am. Chem. Soc. 2014, 136, 13233.
5. R. D. Mukhopadhyay, A. Ajayaghosh, Science 2015, 349, 241.
6. S. Prasanthkumar, S. Ghosh, V. C. Nair, A. Saeki, S. Seki, A. Ajayaghosh, Angew. Chem. Int. Ed. 2015, 54, 946.
7. S. Anjamkudy, V. K. Praveen, K. K. Kartha, V. Karunakaran, A. Ajayaghosh, Chem. Sci. 2016, 7, 4460.
8. P. Anees et al., Chem. Sci. 2016, 7, 0000 (in print).
9. B. Vedhanarayanan, V. S. Nair, V. C. Nair, A. Ajayaghosh, Angew. Chem. Int. Ed. 2016, 55, 0000 (in print).
August 16, 2016
Prof. R. N. Mukherjee, Department of Chemical Sciences, IISER Kolkata
Synthesis and Reactivity of Metal-Coordinated Ligand Radicals
Generation of ligand radicals can lead to interesting ligand-centered reactivity, with the mechanism of galactose oxidase serving as an inspiration for synthetic inorganic chemists. The design of metal complexes to catalyze multielectron reactions usually relies on one or more transition-metal ions capable of two-electron changes in a formal oxidation state. An alternative strategy to multielectron chemistry employs redox-active ligands, as reservoirs of electrons to supply oxidizing or reducing equivalents for bond-breaking and bond-making reactions at coordinatively unsaturated metal complexes.
In this presentation, an account of detailed molecular (X-ray), spectroscopic and magnetic, and reactivity (redox) aspects of a number of ligand radical-coordinated metal complexes involving a group of redox-active ligands to correctly assign the spin-state and/or oxidation level of the metal ion and oxidation level of the coordinated ligands will be discussed. Our designed chelating ligands provide bis-phenolate(2−) and phenoxyl(1−) radical, o-amidophenolate(2−), o-iminobenzosemiquinonate(1−) p radical and o-benzoquinone forms of the coordinating ligands. The electronic structure of the complexes, assigned based on structural, redox and spectroscopic properties is then rationalized by the Density Functional Theory (DFT) and Time-Dependent (TD)-DFT calculations, which successfully rationalize the observed properties of the complexes. Radical-driven reactivity aspects (N–N, C–N, –C–O–C– and –O–C–O– bond formation) will also be discussed.
Selected References:
[1] A. Mukherjee, F. Lloret and R. N. Mukherjee, Inorg. Chem. 2008, 47, 4471-4480.
[2] A. Mukherjee and R. N. Mukherjee, Indian J. Chem. 2011, 50A, 484-490
(Special Issue on Bioinorganic Chemistry).
[3] A. Rajput, A. K. Sharma, S. K. Barman, D. Koley, M. Steinert and R. N. Mukherjee,
Inorg. Chem. 2014, 53, 36-48.
[4] A. Ali, S. K. Barman and R. N. Mukherjee, Inorg. Chem. 2015, 54, 5182-5194.
[5] A. Ali, A. Sengupta and R. N. Mukherjee, J. Ind. Chem. Soc. 2015, 92, 1981-1991 (Special Issue on Professor Animesh Chakravorty’s 80th Birth Anniversary).
[6] A. Ali, S. K. Barman, F. Lloret and R. N. Mukherjee, Inorg. Chem. 2016, 55, 5759-5771.
Protein Folding-Unfolding Dynamics and Hydrophobic Force Law
Folding of an unfolded protein into its complex, but unique and biologically active , three dimensional native state is a non-trivial process. Great progress has been made in recent years in solving the mystery of protein folding and unfolding. One major driving force in protein folding is an effective attraction between the hydrophobic amino acid residues. We shall discuss aspects of this hydrophobic force and its role in protein folding and unfolding dynamics. We shall also discuss how one can tune the hydrophobic force by adding a co-solvent.
There has been a renaissance in the chemistry of lanthanide ion complexes in view of their applications involving photophysical properties, magnetism and catalysis. Both homometallic and heterometallic (3d/4f) lanthanide complexes are being increasingly studied for their magnetic properties in general and as single-molecule magnets (SMMs) in particular. In this talk we will present some of our work on trinuclear 3d/4f complexes which exhibit SMM properties.
