Time-dependent density functional investigation on electronic spectra of 4′-N-dimethylamino-3-hydroxyflavone

The lower singlet excited states for 4′-N-dimethylamino-3-hydroxyflavone (DMA3HF) have been investigated. Theoretical calculations have been performed by using time-dependent density functional theory. The B3LYP and MPW1PW91 functionals with 6-31G(d,p) basis set have been used to compute transition energies. Ground-state geometries are optimized by using density functional theory with both B3LYP and MPW1PW91 functionals combined with 6-31G(d,p) basis set. The first excited state geometries are optimized by using configuration interaction all single-excitations methods with 6-31G(d,p). Vertical absorption energy and excited state electronic dipole moments calculations show that the singlet excited states S1 of the normal of DMA3HF has the character of a large charge separation and effective charge transfer. Calculated emission energies for both the normal and tautomer show a large Stokes shift between the absorption and fluorescence maxima. The present calculations suggest that DMA3HF appears dual fluorescence in gas phase. Our results obtained explain the strong 'dual-fluorescence' feature that involves the excited-state intramolecular proton transfer and charge transfer of DMA3HF.