A theoretical study of the photophysical properties of coumarin-carbohydrazone and coumarin-thiocarbohydrazone

Abstract Absorption and fluorescence properties of the Bis[[7-(diethylamino)-2-oxo-2H- chromene]methylene]-carbonic dihydrazide (CC) and Bis[[7-(diethylamino)-2-oxo-2H-chromene]methyl- ene]-carbonothioic dihydrazide (CTC) have been studied by time-dependent density functional theory (TDDFT). The results indicate that B3LYP/6-311G(d) is the most appropriate method for the current system. The solvent effects are included by the polarizable continuum model (PCM). The absorption wavelengths of CC and CTC in solvents are bathochromic-shift to some extent compared with that in the gas phase. The analysis of molecular orbital transition indicates that the electronic transitions occur mainly in the whole molecule for CC and CTC. The strong absorptions of CC and CTC correspond to a S0 → S1 transition with a π-π* transition characteristic, which is confirmed by natural transition orbital (NTO) analysis. The fluorescence emission is attributed to a S1 → S0 transition, which certifies that Kasha’s rule is followed.