Dynamics simulations of photoinduced proton transfer reactions of 2-(2′-hydroxyphenyl)benzoxazole in the gas phase and its hydrated clusters

The excited-state dynamics simulations of 2-(2′-hydroxyphenyl)benzoxazole (HBO) and hydrated HBO were performed on their lowest energy structures using RI-ADC(2)/SVP-SV(P). For free HBO, only syn-HBO can undergo tautomerization in the excited state. For HBO(H2O), two different pathways (A) the excited-state intramolecular proton transfer (PT) and (B) the excited-state intermolecular PT through hydrogen-bonded network occur. PT time of free HBO is ultrafast at 28 fs, whereas, the PT time of HBO(H2O) takes longer with time range of 43–193 fs depending on the initial structure. The slow PT process of HBO(H2O) is caused by competition between formations of intra- and intermolecular hydrogen bonds.