Ab initio study on the structures and properties of trans- p-coumaric acid in low-lying electronic states

Abstract

The five lowest-lying electronic states of trans- p-coumaric acid have been studied by using the complete active space self-consistent field and multi-reference configuration interaction methods. The adiabatic excitation energies from the ground state to the S 1, T 1, S 2, and T 2 states have been determined in the present study. On the basis of the optimized structures, the calculated energies, and analysis of molecular orbitals, the S 1 and S 2 states were assigned to 1nπ* and 1ππ* in nature, respectively, which are different from the assignment in previous work. The T 1 and T 2 states, which have not been investigated before, were characterized as 3ππ* localized in the C C double bond and the aromatic ring regions, respectively. Photoisomerization dynamics of trans- p-CA should be re-investigated, due to controversy over the character of the excited electronic states.