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

Abstract

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 νC-N + δCH and νC=O modes. The coherent oscillations in the vibrational bands of AAQ strongly coupled to the nuclear coordinate for the TICT process have been observed, which showed its anharmonic coupling to the low frequency out of the plane deformation modes. The vibrational mode of solvent DMSO, νS=O showed a decrease in intensity, especially in the hydrogen-bonded species of DMSO, which clearly shows that the solvation dynamics of DMSO, including hydrogen bonding, are crucial to understanding the reaction dynamics of AAQ with the ultrafast structural changes accompanying the TICT.

Twisted intramolecular charge transfer of nitroaromatic push–pull chromophores

“…S14 in the Supplementary Information, the ν C=C + ν 8a,sym and ν as,NO2 modes also show strong coherent oscillations in the center frequencies, where the similar frequencies of 79 and 146 cm −1 , respectively, were obtained as those from the population dynamics of both vibrational modes. Coherent oscillations in the excited-state vibrational results often represent that the reaction coordinates of the ICT of DNS are strongly coupled to the low-frequency vibrational modes, for example, out-of-plane deformation vibrations relevant to the structural changes of the chromophore in the specific excited-state processes 59 , 63 , 65 , 83 – 87 . Figure S15 in the Supplementary Information lists the out-of-plane deformation modes of DNS in the S 1 excited state with a planar geometry, which can be related to the twist of the nitrophenyl group upon the ICT in the excited state.…”

“…In this work, FSRS with both high spectral (< 10 cm −1 ) and temporal (< 50 fs) resolutions was used to investigate the ultrafast structural dynamics of nitroaromatic push–pull chromophores during the ICT process in the excited state 57 – 59 . The FSRS has been successfully applied in the observation of various ultrafast dynamics in the excited states, including the intra- and inter-molecular proton transfers 60 – 63 , charge transfers 33 , 64 , 65 , etc 66 , 67 . The population dynamics and the peak shifts of the major vibrational modes in the finger-print frequency range would provide sufficient structural information of chromophores in the excited states.…”

Intramolecular Charge Transfer of Curcumin and Solvation Dynamics of DMSO Probed by Time-Resolved Raman Spectroscopy

“…From the kinetic analysis based on the biexponential functions, two fast time constants of 0.11 and 1.8 ps were retrieved for the vibrational Stokes shifts of DMSO. The instantaneous changes in the solvation shells, such as intermolecular hydrogen bonding between the solute and solvent molecules, have been reported in polar protic solvents [27,[52][53][54][55]. Scholes et al reported the inertial solvent responses of water and methanol in the ultrafast time scales of 40-150 fs in the light-harvesting proteins [54].…”

“…Scholes et al reported the inertial solvent responses of water and methanol in the ultrafast time scales of 40-150 fs in the light-harvesting proteins [54]. The coherent oscillations in the vibrational modes of chromophores in protic and aprotic polar solvents have often been interpreted as the solvation dynamics of water or DMSO with the time constants of 190-250 fs, which is considered to facilitate the ultrafast proton and charge transfers in the excited states [27,55].…”

“…The details of a homebuilt Raman setup used for the stimulated Raman measurements are described elsewhere [29,55]. The stimulated Raman probe consists of the broadband (850-1000 nm) femtosecond Raman probe pulses generated by the supercontinuum generation in a YAG window (4 mm thick; Newlight Photonics, North York, ON, Canada), and the narrowband picosecond Raman pump pulses generated by a home-built grating filter (1200 gr/mm).…”