Resonance raman intensity analysis of the excited-state proton-transfer dynamics of 2-hydroxybenzaldehyde in the charge-transfer/proton-transfer absorption band

Abstract

Resonance Raman spectra were obtained for 2-hydroxybenzaldehyde (OHBA) in cyclohexane solution with excitation wavelengths in resonance with the first charge-transfer/proton-transfer (CT/FT) band absorption. These spectra indicate that the Franck - Condon region photodissociation dynamics have multidimensional character with motion predominantly along the nominal C=CH in-plane bend + ring deformation modes (v9, v10, v14, v 16, v18, v19, v20, v26, v30, v31 and v35) accompanied by a smaller amount of motion along the nominal C=O stretch mode (v7), the nominal C=C - C(=O) in-plane bend modes (v33 and v37), and the nominal ring C - O - H in-plane bend modes (v9 and v14). A preliminary resonance Raman intensity analysis was done, and these results for the OHBA molecule were compared to results previously reported for the 2-hydroxyacetophenone (OHAP) molecule. Several proton-transfer tautomers in the ground and excited states were predicted from the results of B3LYP/cc-PVTZ, UB3LYP/cc-PVTZ, and CASSCF/cc-PVDZ level of theory computations. The differences and similarities between the CT/PT band resonance Raman spectra and the vibrational reorganizational energies for the OHBA molecule relative to those for the OHAP molecule are briefly discussed. © 2007 American Chemical Society.