Organic Nonlinear Optical Materials With The Theoretical Molecular Design

Organic nonlinear optical materials have been topic in the recent years. HF/6-31G(d)//TDHF/6-31G(d) is a useful theoretical method for nonlinear optical materials in molecular level. In this thesis, we mainly studied two series molecules that were one-dimensional and two-dimensional charge transfer molecules from the viewpoint of molecular design.The research on the one-dimensional charge-transfer molecules included schiff bases and derivatives of 1,2,3,4- tetrahydroquiazoline (THQ). Both two kinds of molecules had only one D- π -A axis. The positions and kinds of donor-acceptor substituents had significantly effects on molecular first-order hyperpolarizability of Schiff bases. Due to the existence of group -CN-, the intramolecular charge transfer between ground and excited states was unusual. β tot was approximately proportional to the reciprocal of △qCN and the correlation coefficient is -0.83. For THQ, the 6-substituted derivatives were found to have large first hyperpolarizabilities β andthe increasing the conjugation of the molecules could improve the values of β0 /λmax.The effect of heterocycle in the molecules was similar to that of group -NH2, but the hydrogen on the nitrogen atoms could form the hydrogen bond between molecules which could effectively improve the thermal stability.The two-dimensional charge-transfer molecules we studied were the oxygen bridged molecules. The oxygen bridged molecules belonged to the two-dimensional charge transfer system because they had two D- π -A axis and β xxx/β yxx< 1. It was found from the NBO analysis that the substituents and the oxygen atom had significant effect on the molecular first hyperpolarizability. β of two-dimensional charge-transfer molecules were smaller than those of one-dimensional charge-transfer molecules while the thermally stable and visible-transparent for two-dimensional charge-transfer molecules studied were much better.