Resonance hyper-Raman excitation profiles of a donor-acceptor substituted distyrylbenzene: One-photon and two-photon states

Abstract

Resonance Raman and resonance hyper-Raman spectra of the "push-pull" conjugated molecule 1-(4'-dihexylaminostyryl)-4-(4"-nitrostyryl)benzene in acetone have been measured at excitation wavelengths from 485 to 356 nm (two-photon wavelengths for the nonlinear spectra), resonant with the first two bands in the linear absorption spectrum. The theory of resonance hyper-Raman scattering intensities is developed and simplified using assumptions appropriate for intramolecular charge-transfer transitions of large molecules in solution. The absorption spectrum and the Raman, hyper-Rayleigh, and hyper-Raman excitation profiles, all in absolute intensity units, are quantitatively simulated to probe the structures and the one- and two-photon transition strengths of the two lowest-energy allowed electronic transitions. All four spectroscopic observables are reasonably well reproduced with a single set of excited-state parameters. The two lowest-energy, one-photon allowed electronic transitions have fairly comparable one-photon and two-photon transition strengths, but the higher-energy transition is largely localized on the nitrophenyl group while the lower-energy transition is more delocalized.

Surface‐enhanced resonance Raman and hyper‐Raman spectroscopy of water‐soluble substituted stilbene and distyrylbenzene chromophores

“…The hyper-Raman experiments were performed as described in previous publications. 31,32 Hyper-Raman excitation at 850 nm was provided by the fundamental of a picosecond, mode-locked Ti : sapphire laser producing 1-2 ps pulses at 82 MHz. The laser was frequency-doubled to provide excitation for the corresponding RR experiments.…”

“…The aqueous solution Raman and hyper-Raman spectra are nearly identical, although the 1342 cm 1 NO 2 stretching vibration does appear to be slightly more intense in the hyper-Raman than in the RR, consistent with our observations on related molecules. 31,32 The surfaceenhanced spectra exhibit larger differences between Raman and hyper-Raman, mainly in the double-bond stretching region. Interestingly, the photoproduct lines that appear at Table 2.…”

Solvent effects on resonance Raman and hyper-Raman scatterings for a centrosymmetric distyrylbenzene and relationship to two-photon absorption

“…The spectra are similar to those we previously reported for a donor-acceptor substituted distyrylbenzene in which one of the dialkylammonium groups was replaced by NO 2 . 50 The main difference between the spectra of the donor-donor and donor-acceptor molecules is the absence of the strong symmetric NO 2 stretch and the generally much lower intensity of the RHR scattering in the nominally centrosymmetric DSB-C + . The RHR signal from DSB-C + is sufficiently weak that we have not attempted to determine it in absolute units, but we estimate that it is at least an order of magnitude weaker than in most of the conjugated donoracceptor substituted molecules we have studied.…”

“…The experimental setup is described in more detail in Ref. 50. Typical total accumulation times were about 10 min for the linear spectra and 20 min for the nonlinear spectra ͑sums of multiple 2 min integrations for RR and 4 min integrations for RHR͒.…”

“…The RHR signal from DSB-C + is sufficiently weak that we have not attempted to determine it in absolute units, but we estimate that it is at least an order of magnitude weaker than in most of the conjugated donoracceptor substituted molecules we have studied. 33,34,50,52,53 Fluorescence backgrounds have been subtracted from the displayed RR and RHR spectra, and the rather strong fluorescence together with the weakness of the RHR lines leads to spectra with a rather poor signal-to-noise ratio. However, all of the spectral features discussed below were reproducible in spectra obtained on different days from different samples and at slightly different excitation wavelengths.…”