Theoretical Study On The Relationship Between The Structure And Properties Of Novel Two-photon Absorption Materials

In the second half of the 20 th Century, the nonlinear optics as a new branch subject has been born after the invention of the laser, it studies the various nonlinear effect produced by the interaction between laser and materials. One of the main tasks in the field is to find new nonlinear optical materials with even higher efficiency. Scientists have paid more attention to organic molecules than inorganic molecules, due to the characteristic advantages of organic molecular nonlinear optical materials, such as lower dielectric constant, faster response, then the organic nonlinear optical materials field has rapidly developed. At present, the ab-initio quantum chemical theory is the main method to study the nonlinear optical properties of molecular materials. According to the results of many studies, the structure-to-property relationship is established, it can give explanation and prediction to the nonlinear optical properties of molecular materials, thus to direct the experimental synthesis in designing novel molecular materials. Compounds with novel structure always attract more interests, at the same time, isomerism is a common phenomenon in chemistry, recently we found some research about the influence of isomerism on two-photon absorption properties, and the results show that isomerism plays an important role in strongly affecting the nonlinear optical properties. The related research needs a further and systematic investigation.We study the two-photon absorption of some novel organic molecules and the isomer effect on two-photon absorption properties based on the quantum chemical methods, analyze research results in detail. I. The two-photon absorption properties of the novel charge transfer molecules based the divinyl sulfur/sulfone as centerThe two-photon absorption properties of the novel molecules based the divinyl sulfur/sulfone as center have been theoretical studied based on the quadratic response theory. The results indicate that the molecules based the divinyl sulfur/sulfone as center have a strong ability of TPA which can form a new type of TPA molecules. In addition, a molecular structure that significantly improve the TPA cross sections is designed based on the isomerism. II. The effects of isomerism on two-photon absorption of the diazine derivativesThe two-photon absorption spectra of the diazine derivatives has been obtained in gas phase and solvent environments, respectively. The theoretical calculation results show that, whether in the gas phase or solvent, two-photon absorption properties of isomers are different, isomerism not only affects the absorption intensity, but also shifts the absorption peak.This paper is divided into six chapters, the first chapter briefly describes the nonlinear optical phenomenon and the development of two-photon absorption; The second chapter introduces the basic theory of quantum chemistry calculation methods, including the Hartree-Fock method and the density functional theory; In the third chapter, we introduce the optical properties of organic molecules; In the fourth, fifth chapter, our work is divided into two parts, the fourth chapter studies a set of molecules experimental synthesized by the Moncalve's research group which based the divinyl sulfur/sulfone as center at the hybrid density functional level, employing response function method, then we calculate their two-photon absorption cross sections compared with the diphenyl-ethylene molecules which have strong two-photon absorption abilities at the same calculation level. Then a molecular structure is designed that significantly improve the two-photon absorption cross sections based on the isomerism. In the second part, the diazine derivatives are studied, the diazine is a six-member heterocyclic compound with two nitrogen atoms, which has three isomers, they are good electron-withdrawing groups in the molecular structures of push-pull type. Molecules materials containing diazine rings have broad application prospects. We designed the dipole polarity and four moments(including liner and V) structures to carry out our studies, their geometrical structures are optimized and the cross sections are calculated in gas phase and methylene chloride solvent, respectively. The last chapter summaries the work in this thesis and states what can be done in future.