Solvent effect on the initial structural dynamics of benzaldehyde in the S3(ππ*) state-Resonance Raman spectroscopic study

The excited-state structural dynamics of benzaldehyde (BA) after population to the S-3(pi(H-1)pi(L)*) light-absorbing state were studied using resonance Raman spectroscopy and complete active space self-consistent field (CASSCF) calculations. The C-band absorption cross section and the corresponding absolute resonance Raman cross sections in cyclohexane and methanol were simulated using the time-dependent wave-packets formalism, respectively. The results indicate that the major structural dynamics of BA and the homogeneous broadening of the absorption spectrum in cyclohexane are similar to those of BA in methanol or acetophenone (AP) in cyclohexane, whereas the inhomogeneous broadening of BA in cyclohexane is significantly different from that in methanol. It is proposed that the initial decay pathway of BA upon the C-band absorption is mostly towards S3S2 and partly to S-3,S-min. The roles of hydrogen bonding and polar-polar interaction in the spectral broadenings are discussed.