The static and frequency-dependent first hyperpolarizabilities ( ) of Reichardt's betaine dye and two simplest pyridinium-N-phenoxide betaines were computed in the gas phase and in aqueous solution. The sum-overstate formalism was used to calculate individual components of the -tensors. The solvent effect was included via the Langevin dipoles/Monte Carlo approach. The influence of the molecular geometry on the values of the betaine dyes was investigated as well. The calculations demonstrate that the values strongly depend on the interplanar angle between the pyridinium and the phenoxide ring. Moreover, we observed dramatically decreased values of (for all investigated betaines) in aqueous solution as compared to the gas phase.
Fluorescence of nonlinear optical organic single crystal of 3-(1,1-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole (DCNP) excited by a nonabsorbed light pulses from Q-switched Nd:YAG laser λ = 1064 nm as well as absorbed λ = 532 nm light is reported. Two mechanisms of two-photon excited fluorescence are considered: (i) direct two-photon excited fluorescence and (ii) single-photon excitation due to reabsorption of light generated in process of second harmonic generation (SHG) by the crystal due to its nonlinear optical properties. Strong anisotropy of fluorescence that has been observed is linked with uniaxial molecular alignment. Fluorescence decay profile shows two- exponential decay with lifetimes of emitting species of 3.7 and 5.6 ns at 293 K. The excitation and fluorescence spectra of the DCNP single crystal have been measured at 294 K and in function of temperature down to 77.4 K. The strong bathochromic shift of fluorescence spectrum in crystal with respect to fluorescence of DCNP molecule in solution is observed and interpreted with possible formation of molecular aggregates.
A method for calculation of the solvent effect on the molecular
electronic ground-state structure of ions and
molecules has been presented. In this method, being a modification
of the Warshel et al. approach, solvent
molecules are represented by a three-dimensional cubic grid of Langevin
polarizable point dipoles. The
modifications introduced into the original model include (a) the
representation of a solute molecule by atomic
point charges, dipoles, and quadrupoles, (b) the full (i.e., without
dumping) Langevin formula for the
polarization, (c) mutual polarization of the solute and the solvent
molecules, and (d) the Monte Carlo sampling
technique for determination of the optimal position and orientation of
the solute molecule. The proposed
method has been applied in the calculation of hydration energies for
small molecules, ions, α-amino acids,
and DNA bases, as well as in calculations of the solvent effect on the
electronic spectra of acetone,
4-nitroaniline, and Reichardt's betaine dye.
New Fukui functions have been derived within the conceptual density functional theory by the analysis of the polarization effect of a system in static electric field. Resulting Fukui functions accurately reproduce the global softness and electronic dipolar polarizability; they meet the condition integral[f(r)/r]dr = -(partial differential mu/partial differential Z)(N) and lead to very reasonable values of the global hardness for atoms for the group of 29 main group elements. Computational clarity makes the new Fukui functions a promising tool in studies of molecular reactivity.
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