Time dependent density functional theory investigation of the resonance Raman properties of the julolidinemalononitrile push-pull chromophore in various solvents Second molecular hyperpolarizability of 2,2 ′ -diamino-7,7 ′ -dinitro-9,9 ′ -spirobifluorene: An experimental study on third-order nonlinear optical properties of a spiroconjugated dimer Vibrational and nonlinear optical properties of rylenes calculated by ab initio methods J. Chem. Phys. 108, 8662 (1998); 10.1063/1.476305Vibrational contributions to the molecular first and second hyperpolarizabilities of a push-pull polyeneThe linear absorption spectra and absolute resonance Raman excitation profiles of the ''push-pull'' chromophore julolidinemalononitrile have been measured in cyclohexane, 1,4-dioxane, dichloromethane, acetonitrile, and methanol solution at excitation wavelengths spanning the strong visible charge-transfer absorption band. Numerical simulation of the spectra using time-dependent wave-packet propagation methods yields the excited-state geometry changes along the ϳ15 strongly Raman-active vibrations as well as the solvent reorganization energies. The distribution of the total vibrational reorganization energy among the various normal modes is solvent dependent, indicating solvent polarity effects on the electronic structure. These results are compared with those previously obtained for two other push-pull chromophores, p-nitroaniline and julolidinyl-n-N,NЈ-diethylthiobarbituric acid. The frequency dispersion of the molecular first hyperpolarizability, ␤, is also calculated in each solvent using a time-domain form of the standard Oudar-Chemla two-state model modified to incorporate solvent reorganization, inhomogeneous broadening, and the vibronic structure of the charge-transfer state. We show that accurate extrapolation of ␤ measured at frequencies in the near-infrared to zero frequency requires a realistic description of the excited state as the measuring wavelength approaches a two-photon resonance. This is particularly relevant to the high chromophore concentrations needed for device applications, where intermolecular interactions can strongly perturb the electronic transitions.

A resonance Raman intensity analysis is presented for the carbazole/tetracyanoethylene donor-acceptor chargetransfer complex in dichloromethane solution. The intent is to determine the nuclear reorganization contributions to the rates of charge hopping in carbazole polymers used as hole-transport agents in the xerographic (electrophotographic) process. Resonance Raman cross sections have been measured at seven excitation wavelengths spanning the broad visible charge-transfer absorption known to consist of two strongly overlapping charge-transfer electronic transitions. Interference between the Raman amplitudes from these two transitions manifests itself in the Raman excitation profiles for a number of resonantly enhanced modes. Simultaneous modeling of the absorption spectrum and the Raman cross sections shows that explicit consideration of the signs as well as the magnitudes of the normal mode displacements is required to reproduce the experimental data. The signs of the mode displacements obtained from the modeling are shown to be consistent with qualitative predictions based on the nodal patterns of the donor molecular orbitals and the forms of the resonantly enhanced normal modes. Mode-specific reorganization energies for the carbazole donor and tetracyanoethylene acceptor are obtained from the analysis along with parameters describing the magnitude and time scale of the solvent contributions to the reorganization energy. Approximately 60% of the total reorganization energy of 5100 cm -1 in each charge-transfer state is attributed to solvent and any other classically behaved low-frequency modes, with the remainder about equally divided between donor and acceptor modes. The partitioning of the reorganization energy among the carbazole modes is significantly different for the two electronic transitions.

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