Intramolecular Charge Transfer of 1-Aminoanthraquinone and Ultrafast Solvation Dynamics of Dimethylsulfoxide.

The intramolecular charge transfer (ICT) of 1-aminoanthraquinone (AAQ) in the excited state strongly depends on its solvent properties, and the twisted geometry of its amino group has been recommended for the twisted ICT (TICT) state by recent theoretical works. We report the transient Raman spectra of AAQ in a dimethylsulfoxide (DMSO) solution by femtosecond stimulated Raman spectroscopy to provide clear experimental evidence for the TICT state of AAQ. The ultrafast (~110 fs) TICT dynamics of AAQ were observed from the major vibrational modes of AAQ including the ν + δ and ν modes.

Ultrafast intramolecular proton transfer reactions and solvation dynamics of DMSO.

Ultrafast intramolecular proton transfers of 1,2-dihydroxyanthraquinone (alizarin-h) and its deuterated product (alizarin-d) in dimethyl sulfoxide (DMSO) have been investigated by femtosecond stimulated Raman spectroscopy. The population dynamics in the solute vibrational mode of ν and the coherent oscillations observed in all of the skeletal vibrational modes ν and ν clearly showed the ultrafast excited-state intramolecular proton transfer dynamics of 110 and 170 fs for alizarin-h and alizarin-d, respectively. Interestingly, we have observed that the solvent vibrational modes ν and ν may also represent ultrafast structural dynamics at the frequencies for its "free" or "aggregated" species.

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

We report time-resolved stimulated Raman spectra of alizarin in DMSO solution with 403 nm excitation. Upon photoexcitation, 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 ν(C═C) and ν(C═O) show opposite shifts during the reaction, which may implicate changes in the resonance structure of anthraquinone and the attached carbonyl group.