Substituent effects on ultraviolet absorption spectra of 5-substituted Nb-acetyl-1-methoxytryptamines studied by density functional theory calculations

Density functional theory (DFT) calculations were performed for twelve 5-substituted N-b-acetyl-1-methoxytryptamines (5-X: NO2, SO2CH3, CN, CF3, Cl, H, CH3, OH, OCH3, NHCOCH3, NH2, N(CH3)(2)) in methanol. The respective HOMO -> LUMO and HOMO-1 -> LUMO singly excited configurations are mainly responsible for the lowest and the second singlet excited states (S-1 and S-2)Observed UV absorption spectra of 5-H, 5-NHAc, and 5-CH3 derivatives are well predicted by simple time-dependent DFT calculations. Distinct substituent effects are found with respect to the energies of MOs responsible for S-1 <- S-0 and S-2 <- S-0 transitions. Both HOMO-1 and HOMO are destabilized by electron-donating groups, and stabilized by electron-withdrawing groups. LUMO+1 of 5-NO2 derivative should be classified into normal LUMO, which are found for eleven other derivatives as well as indole. Normal LUMO is not significantly affected in energy by electron-donating groups, but stabilized by electron-withdrawing groups.