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Computational and Spectroscopic Studies of Biologically Active Coumarin based Fluorophores.

We used the density functional theory (DFT) calculations to examine various molecular properties of two coumarin derivatives, namely 4-(5-amino-[1,3,4]thiadiazol-2-ylsulfanylmethyl)-7-methyl-chromen-2-one (ATS7MC) and 4-(5-amino-[1,3,4]thiadiazol-2-ylsulfanylmethyl)-7-methoxy-chromen-2-one (ATS7MOC) at different levels of theory and basis sets. The calculated HOMO and LUMO energies reveal that the investigated molecules are chemically active with a tendency for molecular interactions. The theoretical vibrational frequencies of these molecules were found to be consistent with the experimentally obtained frequencies. Moreover, the solvatochromic measurements indicated no significant change in absorption spectral peak by varying the polarity of solvent. However, under the same conditions we find that there is a red shift of 39 nm in fluorescence spectral peak with increase in solvent polarity. The solvatochromic data has been used to estimate excited dipole moments and change in dipole moment is interpreted based on resonance structure of molecules.