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

Abstract

The excited state Raman spectra of 4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) in the locally-excited (LE) and the intramolecular charge transfer (ICT) states have been separately measured by time-resolved stimulated Raman spectroscopy. In a polar dimethylsulfoxide solution, the ultrafast ICT of DCM with a time constant of 1.0 ps was observed in addition to the vibrational relaxation in the ICT state of 4–7 ps. On the other hand, the energy of the ICT state of DCM becomes higher than that of the LE state in a less polar chloroform solution, where the initially-photoexcited ICT state with the LE state shows the ultrafast internal conversion to the LE state with a time constant of 300 fs. The excited-state Raman spectra of the LE and ICT state of DCM showed several major vibrational modes of DCM in the LE and ICT conformer states coexisting in the excited state. Comparing to the time-dependent density functional theory simulations and the experimental results of similar push-pull type molecules, a twisted geometry of the dimethylamino group is suggested for the structure of DCM in the S1/ICT state.

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

“…Similarly, 110 fs dynamics was also observed for the ultrafast decay of the δ NH2, rocking at 1145 cm −1 , and the vibrational relaxation dynamics of 3 ps is further confirmed by the population dynamics of many ICT bands including the bands at 1236, 1340, 1527, and 1590 cm −1 (see Figure S4 in the Supplementary Materials ). Furthermore, the blue-shifts of 3–5 cm −1 that are commonly observed in these vibrational modes show a similar 3 ps vibrational relaxation dynamics in the TICT state, which is generally considered as evidence for the vibrational relaxation in the anharmonic potential surface [ 55 , 58 ]. The differences between the vibrational relaxation dynamics obtained from FSRS and the transient absorption measurements are then considered as the difference between the TICT and the PICT dynamics of AAQ in the S 1 excited state.…”

“…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.…”

The Physical Chemistry and Chemical Physics (PCCP) Section of the International Journal of Molecular Sciences in Its Publications: The First 300 Thematic Articles in the First 3 Years

“…This direction is represented by 39 articles [ 28 , 35 , 129 , 134 , 136 , 190 , 191 , 192 , 193 , 194 , 195 , 196 , 197 , 198 , 199 , 200 , 201 , 202 , 203 , 204 , 205 , 206 , 207 , 208 , 209 , 210 , 211 , 212 , 213 , 214 , 215 , 216 , 217 , 218 , 219 , 220 , 221 , 222 , 223 ]. Their distribution, according to the above types, is presented in Table 7 .…”

“…This expectation is fully consistent with reality, since most of the articles in this direction (31 of 39) are precisely the articles in groups ( b ) and ( c ). Moreover, the articles in group ( b ) constitute the largest part of all the articles related to Thematic Area 6; these include [ 35 , 134 , 190 , 191 , 196 , 197 , 198 , 201 , 203 , 205 , 206 , 207 , 211 , 216 , 217 , 218 , 219 ]. For formal reasons, the list of just cited references can also include the original article [ 208 ] and the review [ 220 ] devoted to graphene and fullerenes, since they all contain carbon–carbon bonds, and, according to the IUPAC standards, they should be classified as organic compounds (although, in general, this means that all chemical compounds consisting of atoms of only one chemical element are traditionally considered objects of inorganic chemistry).…”

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

“…Femtosecond stimulated Raman spectroscopy (FSRS) is a powerful spectroscopic tool for the investigation of vibrational structures of analytes with both high temporal (<50 fs) and spectral (<10 cm −1 ) resolutions [23,24]. FSRS has been successfully applied to various chemical and biological systems where the population or frequency changes of multiple vibrational modes in the fingerprint region reveal ultrafast structural dynamics in the excited states or the structural dynamics of fluorescent proteins upon metal-ion binding [25][26][27][28][29][30]. When combined with electronic spectroscopic methods, including transient absorption and fluorescence upconversion, FSRS can be a useful experimental tool for the structural changes of a molecule accompanying ultrafast electronic transitions in the state [31,32].…”