Modeling the Photophysics and Photochromic Potential of 1,2-Dihydronaphthalene (DHN): A Combined CASPT2//CASSCF-Topological and MMVB-Dynamical Investigation

The photochemical ring opening of 1,2-dihydronaphthalene (DHN) was investigated using two complementary computational approaches. CASPT2//CASSCF minimum energy paths were characterized for reaction channels on the three lowest-energy singlet excited states, describing initial evolution of the spectroscopic bright (ionic) state and its subsequent decay to dark (covalent) states of benzene-like and hexatriene-like character. Although the benzene-like state is unreactive and can radiate, the hexatriene-like state has indirect access to a low-energy conical intersection seam, at which radiationless decay to the ground state and subsequent product formation can take place. An MMVB molecular dynamics simulation was carried out on the reactive hexatriene-like excited state, suggesting that intramolecular vibrational energy redistribution (IVR) controls the radiationless decay and the photoproduct distribution (which is qualitatively reproduced).