Theory Study On Second-order Nonlinear Optical Properties Of Some Organic Molecules With D-π-A Structure

Organic materials with nonlinear optical (NLO) properties are currently attracting considerable attention because of their potential applications in optoelectronic devices of telecommunications, information storage, optical switching, and signal processing. The base study of theoretical and experimental has important scientific meaning and guidance function for improving materials properties, promoting the application process of materials. With the perfection of molecular engineering theory and quantum chemistry calculation method, theoretical research provides useful guidance for experiment. Moreover, theoretical research can provide messages of the relationship between structure and properties by explaining experimental results, and lay a good foundation for further molecule design.As to basic theory, the organic compounds with D-π-A structure reveal good NLO activity by calculating of the NLO property about a series of organic compounds, and these organic compounds has been supposed to be new generation multifunctional NLO materials by more decorating.This paper employed quantum chemistry Density functional theory method and combined with finite field (FF) method to calculate and analyze structures, polarizabilities and second-order NLO properties of organic molecules with D-π-A structure using carboxyl as bridge and carborane derivatives using different group as bridge.(1) Quantum chemistry using DFT B3LYP/6-31G(d) methods was employed to calculate stabilities, polarizabilities and the second-order NLO properties of some D-π-A-conjugated molecules with different substituents R and R substituents at the different positions. The results show that for isomer molecules with different locations of substituent, the molecules are more stable, and the values of polarizability and the second-order NLO coefficient are larger when R substituents and carboxyl conjugated bridge locate at the para-position of benzene ring. However, substituting group position of R has little effect on these physical quantities. For molecules with the same substituting position of R, molecule with bulky R substituents has lager polaricabilityαand dipole moment. In these molecules,during electronic transitions from HOMO to LUMO, the degree of charge transfer is very small. Therefore, the charge transfer between frontier orbitals has little effect on second-order NLO coefficient. Thus these molecular frontier orbitals can qualitatively explain that the second-order NLO coefficients of the molecules are all nearly and small.(2) Density functional theory (DFT) B3LYP at 6-31G* level was employed to optimize the structures of a series of 12-vertex bis-substituted o -dedocarborane derivatives. On the basis of obtaining stable molecular configuration, we combined with finite field (FF) formalism and time-dependent density-functional theory (TD-DFT) to calculate the second-order NLO property and molecular electric spectrum. The results indicate that 12-vertex bis-substituted o -dedocarborane shows the ability to pull electron. When 12-vertex bis-substituted o -dedocarborane was formed D-π-A structure with organic group, it can be regard as a good acceptor. When donor or bridge has fine conjugate property, 12-vertex bis-substituted o -dedocarborane will show powerful ability to pull electron and the second-order NLO response of the molecules will increase.