Resonance Hyper-Raman Excitation Profiles and Two-Photon States of a Donor−Acceptor Substituted Polyene

Abstract

Resonance Raman and resonance hyper-Raman spectra and excitation profiles have been measured for a "push-pull" donor-acceptor substituted conjugated polyene bearing a julolidine donor group and a nitrophenyl acceptor group, in acetone at excitation wavelengths from 485 to 356 nm (two-photon wavelengths for the nonlinear spectra). These wavelengths span the strong visible to near-UV linear absorption spectrum, which appears to involve at least three different electronic transitions. The relative intensities of different vibrational bands vary considerably across the excitation spectrum, with the hyper-Raman spectra showing greater variation than the linear Raman. A previously derived theory of resonance hyper-Raman intensities is modified to include contributions from purely vibrational levels of the ground electronic state as intermediate states in the two-photon absorption process. These contributions are found to have only a slight effect on the hyper-Rayleigh intensities and profiles, but they significantly influence some of the hyper-Raman profiles. The absorption spectrum and the Raman, hyper-Rayleigh, and hyper-Raman excitation profiles are quantitatively simulated under the assumption that three excited electronic states contribute to the one- and two-photon absorption in this region. The transition centered near 400 nm is largely localized on the nitrophenyl group, while the transitions near 475 and 355 nm are more delocalized.

Vibronic coupling simulations for linear and nonlinear optical processes: Theory

“…[51][52][53][54] Solution phase RHRS (Ref. 55) has also been performed for numerous push-pull (donor-acceptor) chromophores [56][57][58][59] and zinc pthalocyanine, 60 applying both Ziegler's vibronic theory and the time-dependent formalism. Non-Condon effects have also been included in the timedependent formalism to describe OPA and RRS (Refs.…”

“…12, 13, and 61-63) and to a lesser degree RHRS. 58, 64 Shoute et al 58 examined RHRS of push-pull donor-acceptor complexes, using a model where the intermediate state of the twophoton excitation was assumed to be a vibrational level of the ground electronic state. A recent investigation of RHRS for the fluorescent dye rhodamine 6G illustrated that non-Condon terms can be larger than FC terms in circumstances when oneand two-photon transitions are not simultaneously strong.…”

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

“…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.…”

Two-photon resonant hyperpolarizability of an H-shaped molecule studied by wavelength-tunable hyper-Rayleigh scattering

“…Based on the difference of dynamic properties between instantaneous HRS and decline TPF, Noordman and vanHulst used time-resolved detection technology to suppress TPF in HRS experiment. [40][41][42] In this work, we also use a spectrometer to eliminate the two-photon fluorescence component to the HRS signal. In addition, this approach was implemented in a frequency domain by Olbrechts et al to suppress TPF.…”