Vibronic effects on solvent dependent linear and nonlinear optical properties of push-pull chromophores: Julolidinemalononitrile

Abstract

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.

Excited state molecular dynamics simulations of nonlinear push–pull chromophores

“…The linear dependence of the conjugated bond lengths of Table 5 on the basis state composition is strong; only plots of the nitrile bonds as a function of f eq had correlation coefficients less than 0.965. The variability of the number of modes observed experimentally between the solvents negates the possibility of a straightforward comparison of projected excited state geometries with the simulated solvent dependence of the coordinates [15].…”

“…The calculated solvatochromic shifts of JTB are in better agreement with the experimental measurements than in either of the other two molecules. However, the shifts of JTB are calculated at an identical geometry in all solvents, whereas the [14][15][16], respectively. c Ref.…”

“…In addition, an amino wag angle and single bond and double bond twist angles were defined for JM as (180 À D (2, 1, 8, 3))/2, D (12,13,14,15), and D (13, 14, 15, 17), respectively. As in PNA, the amino wag angle is strongly correlated to the hybridization of the amino nitrogen; a decrease in this angle signifies the evolution from sp 3 to sp 2 hybridization, sp 2 hybridization being associated with the zwitterionic basis state.…”

“…In addition, in all solvents the single bond twist angle decreases and the double bond twist angle increases in the excited state relative to the ground state, indicating a greater degree of zwitterionic character in the excited state. In order to evaluate the magnitudes of the calculated coordinate changes, the experimental normal mode displacements of JM [15] were projected onto a basis of B3LYP/6-311G** normal modes. The MD results were used to constrain the directions of the conjugated bond length changes and thus eliminate most of the 131,072 possible geometries (see Section 2).…”

“…Recently, the resonance Raman technique was applied to p-nitroaniline (PNA) [14], julolidinemalononitrile (JM) [15], and julolidinyl-n-N, N 0 -diethylthiobarbituric acid (JTB) [16]. These analyses derive the dimensionless displacements between the ground and excited state potential surfaces for all the active vibrational modes by simultaneously fitting the absorption spectrum and Raman excitation profiles with an empirical model defined by a common set of parameters [17].…”