Ultrafast Intramolecular Proton Transfer of Alizarin Investigated by Femtosecond Stimulated Raman Spectroscopy

Abstract

We report time-resolved stimulated Raman spectra of alizarin in DMSO solution with, 403 nm excitation. Upon photo excitation, the intramolecular proton transfer reaction of alizarin occurs in 70-80 fs, which is, confirmed by both the population growth and the frequency and bandwidth changes of skeletal vibrational modes of alizarin. Interestingly, the vibrational frequencies of v(C= C) and v(C=O) show opposite shifts during the reaction, which may implicate changes, in the resonance structure, of anthraquinone and the attached-carbonyl group. Vibrational relaxation in the potential surface of the proton transferred tautomer of alizarin and the population decay occurring-with two distinct time scales were also observed in addition to the solvation dynamics of DMSO solvent molecules.