Theoretical Studies On Two-photon Absorption Properties Of New Type Organic Molecular Materials

It has become an important project to find new nonlinear optical materials with strong nonlinear optical properties and quick response behavior due to their attractive applications foreground, for instance, in modern laser technology, optical communication, data storage, optical information processing, 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 waveband, good flexibility, high optical damage threshold, low cost, and easy combination and modification. The rapid development of modern quantum chemical theory at ab-initio level has also led to the rapid development of theoretical study on nonlinear optical properties of molecular materials. Theoretical studies not only can forecast the nonlinear optical properties of the already existed molecular materials, but also can easily design many new molecular materials with exceptional properties and provide guide lines for experimental syntheses.The study on optical properties of the organic molecular material has made great progress recently. Many organic molecular materials with strong nonlinear optical properties have been synthesized and their structure-property relations have been explored. As a new nonlinear optical material, the excellent nonlinear optical properties of organic dibenzothiophene derivatives have been discovered. The special structure-property relation of organic dibenzothiophene derivatives needs to be theoretically studied.The thesis studies the linear and nonlinear optical properties of a variety of newly synthesized organic dibenzothiophene derivatives and series of compounds based on pyridine utilizing theoretical and computational approaches on the base of the density functional theoretical level, represents the relation of the molecular structures and properties, investigates the solvent effects on the molecular geometry structures and optical properties, and discusses the relation of the charge-transfer activity and molecular properties by analyzing the molecular charge-transfer process. The content of this thesis is as follows. The first chapter gives a brief introduction of nonlinear optics and also the developing process of the nonlinear optics and nonlinear optical materials. In the second chapter, some basic of quantum chemical theory is introduced, which mainly focuses on Hartree-Fock approximation and density functional theory. The different approaches developed recently for calculating molecular nonlinear optical properties are summarized in the third chapter, including sum-over-state, few-state model response theory methods. The fundamental ways of representing the solvent environment are discussed in the forth chapter. The research process and the results of dibenzothiophene derivatives are given particularly and the results are discussed and compared with the experimental results in the fifth chapter. Nonlinear optics properties are studied on pyridine in the sixth chapter. The summary and prospect are represented in the last chapter.