Studies of the S1 state in a prototypical molecular wire using picosecond time-resolved spectroscopiesElectronic supplementary information (ESI) available: time-resolved emission spectra, and transient absorption spectra. See http://www.rsc.org/suppdata/cc/b3/b307005k/

Abstract

Picosecond time-resolved resonance Raman spectroscopy, TR3, reveals an intense acetylenic band in the S1 state of the prototypical molecular wire 1,4-bis(phenylethynyl)benzene.

Mode specific excited state dynamics study of bis(phenylethynyl)benzene from ultrafast Raman loss spectroscopy

“…All measurements were carried out in the 1000-2200 cm 1 spectral window to monitor the changes in the high frequency modes. The strongest vibrational modes observed in this experiment were at 2126, 1573, 1173, and 1130 cm 1 , which agree well with the excited state resonance Raman spectrum reported by Beeby et al 24 These bands have been assigned to localized FIG. 6.…”

“…[21][22][23] Partially structured absorption and emission spectra were observed at room temperature in solutions and this has been attributed to S 0 -S 1 transitions of the same molecule with different structural conformations. 21,24 In the ground state, the rotational barrier around the sp 2 -sp CC single bond is very low; it was determined by Greaves et al to be 220-235 cm 1 from a jet spectroscopy experiment, and this number agrees with the AM1 calculations of Levitus (0.5 kcal/mol = 180 cm 1 ). 25,26 Therefore, all rotamers ranging from planar to twisted forms are likely to co-exist at room temperature, resulting in electronic transitions at different energies.…”

“…24,25 In general, transient absorption provides information on the time dependent response due to the population dynamics and/or conformational changes in the excited electronic states. However, any involvement of the Franck-Condon active vibrational modes remains invisible under the broad excited state absorption bands, which makes it difficult to elucidate the structural vibrations involved during the time dependent nuclear dynamics.…”

“…The narrow-band Raman pump (ps pulses) was generated using a 4f-grating pair configuration. 24 This study was performed with 300 nJ Raman pump pulses having [15][16][17][18] (FWHM). For the current URLS measurements, the Raman pump was tuned to 622 nm which is the peak wavelength obtained from transient absorption measurements with 307 nm photo pump (PP) excitation.…”

“…Those time resolved fluorescence studies showed a slow (tens of picoseconds) rising component that has been attributed to structural reorganization in the excited electronic state. 24 Thus, in order to better understand the structural dynamics of the photophysical states, we have explored the excited electronic state dynamics of BPEB using femtosecond transient absorption (TA) and the vibrational mode-dependent dynamics usingultrafastRamanlossspectroscopy(URLS).URLSisanalogous to femtosecond stimulated Raman spectroscopy (FSRS) but the Raman spectra are measured in the anti-Stokes region with high signal-to-noise ratios. [29][30][31][32][33][34][35][36][37][38][39] Based on the literature, it was expected that in the excited state major conformational changes could occur.…”