Ab initio study of excited-state intramolecular proton dislocation in salicylic acid

摘要: Abstract The potential-energy (PE) function of the S 1 (ππ ∗ ) state along reaction path for excited-state intramolecular proton-transfer process in salicylic acid (SA) has been calculated by ab initio electronic-stucture theory based on multi-reference perturbation (CASPT2 method). CI-singles (CIS) method employed to construct minimum-energy S1 PE surface. results provide a particularly clear-cut demonstration importance proper inclusion dynamical electron correlation effects calculation photochemical functions. absorption and emission wavelengths are excellent agreement with experiment. calculations predict single minimum surface, rather than two (enol keto) minima found previous semiempirical calculations. corresponds shift H atom only about 0.15 A OH bond respect equilibrium ground state. photophysics SA is thus better described as an vibrational relaxation transfer hydrogen atom. It that most Stokes fluorescence arises from rearrangement H-chelate ring.