TDDFT and MS‐CASPT2 Study of the Excited States of Para‐Methoxymethylcinnamate

Abstract

The vertical and adiabatic excitation energies of the ππ*, ππ*′, and nπ* states of the trans and cis isomers of para‐methoxymethylcinnamate (p‐MMC) were calculated using time‐dependent density functional theory and multistate complete active space second‐order perturbation theory (MS‐CASPT2) with reasonably sized basis sets. The adiabatic excitation energies of the ππ* state of trans‐p‐MMC calculated by TD‐CAM‐B3LYP and MS‐CASPT2 are in excellent agreement with the experimental value. The nπ* state lies at a higher energy than the ππ* state in the adiabatic excitation energy calculations, indicating that the barrier to internal conversion from the ππ* state to the nπ* state will be considerable. This result is opposite to the previous theoretical result. The microsolvation effect of a water molecule on p‐MMC is examined by calculating the excitation energies. The origin of the stabilization of the ππ* state and destabilization of the nπ* state by microsolvation has also been elucidated using natural population analysis.