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

The exited state (μe) 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 (μe) 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 (μg) 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 μg and μe were calculated using the solvatochromic shift method and μe was also determined in combination with μg. It was observed that μe were greater than those of μg, indicating a substantial redistribution of the π-electron densities in a more polar excited state for this coumarin. Further, the changes in dipole moment (Δμ) were calculated both from the solvatochromic shift method and on the basis of microscopic empirical solvent polarity ([Formula: see text]) and the values are compared.

Solvent effect on the dipole moments and photo physical behaviour of 2,5-di-(5-tert-butyl-2-benzoxazolyl) thiophene dye

The absorption and emission spectra of fluorescent thiophene dye, namely, 2,5-di-(5-tert-butyl-2-benzoxazolyl) thiophene, have been recorded at room temperature in solvents of different polarities. The excited state dipole moments (μe) were estimated from Lippert’s, Bakhshiev’s, and Kawski–Chamma–Viallet’s equations using the variation of Stoke’s shift with the solvent dielectric constant and refractive index. The optimized geometry of the molecule and μg were calculated theoretically by Gaussian 03 software using B3LYP/6-31g* level of theory. The μg and μe were calculated by means of solvatochromic shift method and μe was determined in combination with μg. It was observed that μe were higher than those of the μg, indicating a substantial redistribution of the π-electron densities in a more polar excited state for the selected thiophene dye. Further, the change in the dipole moment (Δμ) was calculated both from solvatochromic shift method and on the basis of microscopic empirical solvent polarity parameter [Formula: see text] and values are compared.