Dipole moments of the lowest excited singlet and triplet states of 2,4,5-trimethylbenzaldehyde in a durene host crystal

Abstract

From Stark spectra, the differences in dipole moments between the ground state and the lowest singlet and triplet excited states of 2,4,5-trimethylbenzaldehyde isolated in a durene host crystal are determined within a precise Lorentz local field approximation to be 1.65 ± 0.09 D and 1.05 ± 0.06 D, respectively, for the most prominent sites. Neither dipole moment change is parallel to the carbonyl axis, but the change for the singlet state has the largest component along this axis while that for the triplet state does not. These data are consistent with the assignment of these states as primarily 1nπ* and 3ππ*. The dipole moment of the ground state was determined to be 3.53 ± 0.05 D from dielectric constants of benzene solutions.