Photophysical characteristics of two novel coumarin derivatives: Experimental and theoretical estimation of dipole moments using the solvatochromic shift method

The exited state (mu(e)) dipole moment of a molecule is an important parameter, which gives information about electronic and geometrical structure of the molecule in the short-lived state. We have experimentally estimated the exited state (mu(e)) dipole moment of two novel coumarin derivatives, namely, diethyl 2-acetamido-2-((6-methyl-2-oxo-2H-chromen-4-yl)methyl)malamute (DAM) and 5,6-Benzo-3-[1-(4,5-dicarbomethoxy-1,2,3-triazoloacetyl)] coumarin (5BDTC) by three methods, namely, Lippert's, Bakhshiev's, and Kawski-Chamma-Viallet's. In the Solvatochromic shift method, spectral shift is due to internal excitation of the molecule. We have recorded absorption and emission spectra of the above two novel coumarin derivatives at room temperature using solvents of different polarities. The geometry of the molecules were fully optimized and the ground state dipole moment (mu(g)) were also calculated theoretically by Gaussian 03 software using B3LYP/6-31g* level of theory. The excited state dipole moment was calculated using CIS/6-31G* level of theory. The mu(g) and mu(e) were calculated using the solvatochromic shift method and mu(e) was also determined in combination with mu(g). It was observed that mu(e) were greater than those of mu(g), indicating a substantial redistribution of the pi-electron densities in a more polar excited state for this coumarin. Further, the changes in dipole moment (Delta mu) were calculated both from the solvatochromic shift method and on the basis of microscopic empirical solvent polarity (E-T(N)) and the values are compared.