The DFT Study On Second-order NLO Property Of The Organic Molecules With Schiff Base And Heterocycle

Traditional optics is the science which researching weak light of diffuse rule in medium, as the birth of laser and the rapid development of laser technology, nonlinear optics becomes an important embranchment of the field of modern optics, in which the interaction of intense laser with matter is studied. At the same time, it has become an important project to find new nonlinear optical (NLO) materials, due to their wide use and attractive application foreground, for example, in laser frequency doubling, laser frequency mixing, parametric amplification and oscillation, integrated optics, optical communication, and other fields. Much emphasis has been put on organic nonlinear optical materials because they have many advantages,such as large nonlinear optical coefficient,wide response wave band,good flexibility,high optical damage threshold,low cost,and easy combination and modification.The nonlinear optical material of early study mostly focused on inorganic crystal material, which has the merit that the compositive physical chemistry capability is better, such as single crystal grow jumbo size, chemical stability higher, optics homogenized, the well phase-matching, et al. The polarization of inorganic material is made by distortion of crystalline lattice, long response time and low nonlinear optical coefficient, the inorganic nonlinear optical crystal of practical apply is few. The nonlinear optical response of organic and macromolecule nonlinear material roots in polarization of delocalization and conjugatedπ-electron in the interaction of lightfields, so the material has the speedy response, high nonlinear optical coefficient and the structure of organics is multivariate, which designing molecule according to need, customizing molecular structure of specific functional. Comparing inorganic material, the organic nonlinear optical material possess the merit that high nonlinear coefficient, short photic response time, small dielectric constant, easy designing and processing, study and preparation new organic nonlinear optical material is the import object of material science. In recent years, the developing of organic material is quick, formed ramose subject of"molecular nonlinear optical".Organic second-order nonlinear optical material has the merit that high nonlinear optical coefficient, cutting out the molecule, become the focus which practical appliance of the nonlinear optical material of high efficiency. Organic second-order nonlinear optical material is make up of electro-donor, electro-receptor and conjugatedπ-electron which is use to join the electro-donor and electro-receptor commonly, the change of second-order nonlinear optical coefficient mostly by increasing ability of electro-donor and electro-receptor, changing the performance of conjugate bridge. So we calculate and analyze second-order nonlinear optical properties on series of the organic molecules with Schiff base and heterocycle in this paper. The results of our studies in this thesis are:1. Density functional theory (DFT) B3LYP at 6-31G* level was employed to optimize the structures of a series of Y-shaped organic heterocyclic molecules with thiazole chromophore and Schiff base. On the basis of the obtained stable molecular configuration, we combined with finite field (FF) formalism and time-dependent density-functional theory (TD-DFT) to calculate and analyse the NLO properties and electric spectrum of molecules. The results show that the molecules possess the A-π-D-π-A constructure, when the length of conjugate bridge of the branched chain and the conjugated effect of chromophore increase, the dipole moment of ground state, polarizability and the second-order NLO coefficient (β) of the molecules will increase. Simultaneously, theβtot of the series of organic heterocyclic molecules is related to energy gap of frontier molecular orbital, the energy gap of frontier molecular orbital is smaller; the value ofβtot is larger.2. Density functional theory (DFT) BHandHLYP at 6-31G* level was employed to optimize the structures of three kinds ofΛ-shaped molecules with six-membered carboatomic ring and Schiff base. On the basis of obtaining stable molecular configuration, combined with finite field(FF) method and time-dependent density-functional theory(TD-DFT), the second-order nonlinear optical(NLO) property and molecular electric spectrum were calculatd. The results indicate that when the conformation of cyclohexane of inflexion is different, the charge distrbution, the dipole moment, the polarizability, the second-order NLO coefficients and the electric spectrum of molecules are slight variational. The molecule with benzene of inflexion is different from the molecules with cyclohexane of inflexion, when the substituting group R of branched chain is increscent, the polarizability and second-order NLO coefficient are more explicit increase.