| With the rapid development of optical telecommunication, optical computing and signal-processing devices etc, materials with larger nonlinear optical coefficient are still in great demand due to the critical role that they are playing in photoelectric devices. The metal complexes are of major interest in the nonlinear optical field, due to their large nonlinear optical coefficient, fast nonlinear optical response times, relatively low cost, ease of fabrication and integration into devices, tailorability which allows one to fine tune the chemical structure and properties for a given nonlinear optical process, high laser damage thresholds. Theoretical calculation can be a good tool for obtaining some insight into molecular property, each tensor component of hyperpolarizability can be assessed directly, unlike optical experiment in which the property is obtained as macroscopic quantity. Usually, a macroscopic quantity cannot be directly converted to a microscopic one due to intermolecular or collective effects. Therefore, calculation of molecular hyperpolarizabilities and comparison of the results with corresponding experimental results are of importance in establishing the structure-property relationship and estimating the amount of such effects on molecular optical nonlinearity.In this thesis, we have performed systematic theoretical research of novel dinuclear d10 transition metal acetylides nonlinear optical materials by using time-dependent density-functional theory combined with sum-over-states method (TDDFT-SOS). On the basis of the optimized molecular geometries, electronic spectrum, charge transport and nonlinear optical properties of these systems are obtained and structure-property relationships are also established. These results may provide a theoretical basis of designing novel materials with large nonlinear optical coefficeents. Our work has been focus on the following three aspects: 1. The nonlinear optical properties of a series of organic molecules are calculated by using TDDFT-SOS method and compared with the literature theoretical and experimental values. The results show that our theoretical values are in agreement with the experimental and CCSD(T) ones. This indicates we can use TDDFT-SOS method to study the NLO properties of the organic systems. The effects of different functional/basis set on NLO properties were tested. Moreover, the convergent behaviors and efficiency of various functionals are also discussed.2. We have investigated the electronic structure and the third-order nonlinear optics properties of the dinuclear metal acetylides [H3PM(C≡C)nMPH3](M=Cu, Ag, Au) and elucidated structure-property relationships from the micromechanism. Compared between Cu, Ag, and Au, Au atom acting as center is superior to others. Enhancing the length of conjugation is an effective way to promote the nonlinear optical response. According to the three-state approximation, enhancing the conjugation length decreases the transition energies, which is the major factor to enhancing the third-order polarizabilities. From the standpoint of the values of our studied complexs, they can become excellent third-order nonlinear optical materials.3. The nonlinear optical properties of a series of digold alkynyl complexes having"aurophilic attraction"are calculated by using TDDFT-SOS method. The results show that the third-order nonlinear optical properties of metal complexes are depending on their structures, the molecules owning long conjugated chains have large NLO coefficient. The influence of"aurophilic attraction"to NLO properties can not be neglected. Our study can indicate that electronic charge has been localized on the two Au atoms by the Au…Au interaction, which connected the"D-A"and"A-D"molecular moieties to the"D-A-A-D"molecule, and extended the delocalized scopes of electronic charge on the molecular framework, indicating that the Au-Au interaction plays an important role in NLO properties of the model systems.
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