Physical origin of the third-order nonlinear optical properties of polyenes

International audienceThe results of an experimental study of the third-order nonlinearity and second-order hyperpolarizabilities for several π-conjugated polyenes are given. In this paper we present also a theoretical analysis of the second-order hyperpolarizabilities of polyenes modified. Theoretical calculations of the were carried out at the restricted Hartree–Fock level using the semiempirical Austin model 1 and parametric method 3 (PM3) quantum-chemical self consistent field–molecular-orbital approaches within the HyperChem 7.0 program package. Calculations based on the PM3-type semiempirical molecular-orbital approach have been performed to investigate the energy and structural stabilities of polyenes. We have calculated electronic charge-density distributions of these molecules. Calculations have unambiguously shown an essential influence of modifications of the double bonds and distribution of electronic charge density. Moreover, we have observed a substantial change in the charge-density gradients under the influence of aromatic ring modifications. Changes in the charge-density gradients leads to a strong non-uniformity of the space electronic charge distribution. In the performed calculation we predict that the third-order nonlinearity and second-order hyperpolarizabilities increase with increasing elongation of polyene chain. We found that the theoretical calculations give a true tendency for changes in the corresponding susceptibilities; however, the values are different because of the underestimated absolute energy gap values obtained within the semiempirical methods

Photoinduced Nonlinear Effects in C60\text{}_{60}-2-thioxo-1,3-di thiole and C60\text{}_{60}-TTF Derivatives

Photoinduced effects in pure C$\text{}_{60}$:C$\text{}_{60}$-TTF and C$\text{}_{60}$-2-thioxo-1,3-dithiole cycloadducts are investigated using nonlinear optical techniques. We have studied photoinduced optical second harmonic generation, two-photon absorption, linear electro-optics, and quadratic electro-optic effect coefficient versus applied pressure (p) and temperature (T). We deduce the influence of the grafted substituents in pure C$\text{}_{60}$ on the observed photoinduced effects. The obtained results illustrate clearly that the photoinduced nonlinear optics can be used as a tool to detect structural changes at low temperature in modified C$\text{}_{60}$. We have unambiguously demonstrated that, under the applied hydrostatic pressure up to 19 GPa and the temperature from 4.2 up to 150 K, the observed effects are essentially caused by the grafted TTF derivatives.zapisz i

Photoinduced Nonlinear Effects in C 60

Photoinduced effects in pure C$\text{}_{60}$:C$\text{}_{60}$-TTF and C$\text{}_{60}$-2-thioxo-1,3-dithiole cycloadducts are investigated using nonlinear optical techniques. We have studied photoinduced optical second harmonic generation, two-photon absorption, linear electro-optics, and quadratic electro-optic effect coefficient versus applied pressure (p) and temperature (T). We deduce the influence of the grafted substituents in pure C$\text{}_{60}$ on the observed photoinduced effects. The obtained results illustrate clearly that the photoinduced nonlinear optics can be used as a tool to detect structural changes at low temperature in modified C$\text{}_{60}$. We have unambiguously demonstrated that, under the applied hydrostatic pressure up to 19 GPa and the temperature from 4.2 up to 150 K, the observed effects are essentially caused by the grafted TTF derivatives.zapisz i