Hydrogen-bonded Intramolecular Charge Transfer Excited State of Dimethylaminobenzophenone using Time Dependent Density FunctionalTheory

Density functional theory and time-dependent density-functional theory have been used to investigate the photophysical properties and relaxation dynamics of dimethylaminobenzophe-none (DMABP) and its hydrogen-bonded DMABP-MeOH dimer. It is found that, in non-polar aprotic solvent, the transitions from S₀ to S₁ and S₂ states of DMABP have both n→π^* and π→π^* characters, with the locally excited feature mainly located on the C=O group and the partial CT one characterized by electron transfer mainly from the dimethylaminophenyl group to the C=O group. But when the intermolecular hydrogen bond C=O…H-O is formed, the highly polar intramolecular charge transfer character switches over to the first excited state of DMABP-MeOH dimer and the energy difference between the two low-lying electronically excited states increases. To gain insight into the relaxation dynamics of DMABP and DMABP-MeOH dimer in the excited state, the potential energy curves for con-formational relaxation are calculated. The formation of twisted intramolecular charge trans-fer state via diffusive twisting motion of the dimethylamino/dimethylaminophenyl groups is found to be the major relaxation process. In addition, the decay of the S1 state of DMABP-MeOH dimer to the ground state, through nonradiative intermolecular hydrogen bond stretching vibrations, is facilitated by the formation of the hydrogen bond between DMABP and alcohols.