Photophysics of fluorescent molecules and their application in the study of microenvironments
We have studied various classes of molecules: porphyrins, benzimidazoles, aminoquinolenes and most recently, Schiff bases.
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Our early research focused on chlorin p6 and purpurin 18, derived from chlorophyll. These are potential second generation drugs for photodynamic therapy. Using fluorescence spectroscopy, we studied their binding with drug delivery vehicles and blood plasma, Hence, a Trojan horse mechanism responsible for their selective localization in tumor tissues was proposed.
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2-substituted benzimidazoles undergo solvent mediated proton transfer in mildly acidic conditions. They have been used to study the dynamics of protons in the nanochannels of nafion membrane. It has been established that electrostatic attraction plays a significant role in decreasing the ionic mobility of cations in these nanochannels, at low levels of hydration.
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Aminoquinolines exhibit interesting excited state dynamics involving a flip flop motion and an intramolecular charge transfer. The dynamics is strongly dependent on the nature of the solvent as well as whether the amino substitution is in the homoatomic ring or the heteroatomic ring.
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The primary photoprocess in epicocconone, a protein stain, has ben identified as ultrafast photoisomerization,In its aducts with proteins, this process is not important and the excitation is not of p-p* type. Rather, the flexing of the ring has ben found to take the molecule to a long lived emissive excited state.
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The existing anomaly about the emission property of salophen, a Schiff base, has been removed by careful purification. Significant incrase in fluorescence lifetime in its aluminum complex, compared to that in its zinc complex, has been rationalized by a monomer dimer equilibrium. Hence, fluorescence lifetime rather than intensity has been proposed to be a good parameter for sensing aluminum with salophen.
Ultrafast processes in silica nanoparticles and dye-silica nanoconjugates
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The blue photoluminescence of silica nanostructures has ben assigned to the interplay of a defect pair and other emissive trap states. The trapping process has been found to be responsive to simple chemical inputs like organic solvents. It is favored strongly by mineral acids.
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Dye silica nanoconjugates are being prepared in order to study their prospect as light harvesting nanoantennae. The operation of Forster resonance energy transfer within these aggregates has been established. Efforts are on to develop complete artificial photosynthetic systems by bringing about photoinduced electron transfer between these and electron acceptors like graphene.
Excited state dynamics for photovoltaic applications
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Graphene quantum dots, semiconductor quantum dots, perovskites and conjugated polymers have potential photovoltaic applications. The initial processes taking place in these systems are of utmost importance in this regard. We have initiated the study of these systems using ultrafast trasnient absorption and photoluminescence techniques.