Ultrafast intramolecular proton transfer reactions and solvation dynamics of DMSO

Abstract

Ultrafast intramolecular proton transfers of 1,2-dihydroxyanthraquinone (alizarin-h2) and its deuterated product (alizarin-d2) in dimethyl sulfoxide (DMSO) have been investigated by femtosecond stimulated Raman spectroscopy. The population dynamics in the solute vibrational mode of νC=O and the coherent oscillations observed in all of the skeletal vibrational modes νC=O and νC=C clearly showed the ultrafast excited-state intramolecular proton transfer dynamics of 110 and 170 fs for alizarin-h2 and alizarin-d2, respectively. Interestingly, we have observed that the solvent vibrational modes νS=O and νCSC may also represent ultrafast structural dynamics at the frequencies for its “free” or “aggregated” species. From the kinetic analysis of the νS=O and νCSC modes of DMSO, the ultrafast changes in the solvation or intermolecular interactions between DMSO molecules initiated by the structural changes of solute molecules have been thoroughly investigated. We propose that the solvent vibrational modes νS=O and νCSC of DMSO can be used as a “sensor” for ultrafast chemical reactions accompanying the structural changes and subsequent solute-solvent interactions.

Twisted Intramolecular Charge Transfer State of a “Push-Pull” Emitter

“…A home-built FSRS setup based on a 1 kHz Ti:sapphire regenerative amplifier has been used for time-resolved Raman measurements [43,44]. The broadband Raman probe was generated by supercontinuum generation in an yttrium aluminum garnet crystal (4 mm thick, Newlight Photonics, Toronto, ON, Canada) and filtered by a long pass filter (830 DCLP, Omega Optical).…”

“…Since Mathies and co-workers first introduced the femtosecond stimulated Raman spectroscopy (FSRS) to the ultrafast dynamics and transient Raman measurements of all-trans-β-carotene in the S 2 and S 1 excited states [39,40], FSRS with both high spectral (<10 cm −1 ) and temporal (<50 fs) resolutions has been widely applied to many excited state processes including the intra-and inter-molecular proton transfers [41][42][43][44], charge transfers [45][46][47][48], electron transfers [49][50][51][52]. A broadband Raman probe pulses combined with a narrowband Raman pump were used for FSRS, and the transient Raman bands of the ground and excited electronic states can be obtained at the same time in a wide frequency range covering most of the fingerprint region (800-2200 cm −1 ) [43,53].…”

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

“…The 560 ps component represents the fluorescence lifetime which is similarly observed from the decay of GSB. The 4.7 ps component is considered as the vibrational relaxation dynamics in the ICT state, which is often observed for small organic chromophores in the excited-state potential surface [ 48 , 53 , 54 , 55 , 56 ]. Then, the fastest 180 fs component can be assigned as the ICT dynamics of AAQ in the S 1 state.…”

“…Thus, all the spectral changes of AAQ are interpreted as the ICT in the excited state rather than the ESIPT. The vibrational assignments of the excited-state vibrations of AAQ were mostly based on the TDDFT simulations and the previous reports on dihydroxyanthraquinone (see Figure S7 in the Supplementary Materials for details) [ 48 , 56 ].…”

“…Effective solvation may facilitate chemical reactions, and vibrational cooling can stabilize the product state by dissipating the excess vibrational energy after chemical reaction [ 43 , 44 ]. Coherent nuclear wavepacket motions, resulting from the strong solvation via hydrogen bonding, have been reported for chemical reactions in the solution phase [ 45 , 46 , 47 , 48 ].…”