The DFT Study On Second-order NLO Property Of The Schiff Base Ligand And Ⅷ Metal Complexes

The 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. Simultaneously, new requests about the study on NLO property are brought forward.Molecule-based materials with chemical modified properties are the studied field of modern high technology and novel material. The metal complexes with organic and inorganic merit have been attracted a lot of attention because of the potential NLO properties. Comparing to the pure the organic molecules, complexes molecules can offer a very large variety of NLO structures in relation to the metal d configuration, oxidation state and spin state, etc. All of these structures not only can increase the NLO properties, but can also enhance the environmental stability.The development of the molecular engineering theory and the perfection of the quantum chemistry computational technology provide a powerful tool to explore the relation between the molecular electronic structures and properties, in order to offer the credible schemes and data for experiments, which further builds a foundation for the molecular design.Schiff base complexes are an important type of NLO materials; there are many conclusions of those Schiff base complexes of NLO properties have been obtained by the experimental and theoretical studies. However, the mono Schiff base complexes are not been studied roundly. The studies of the relation between the electronic structure and NLO properties of those complexes would promote the exploitations and applications of its NLO properties.Hence, we calculate and analyze the second-order NLO properties of the Schiff base complexes with planar structures and tetrahedral structures in this thesis. The aims of my thesis work are:(1) To calculate the electronic structures and second-order NLO properties of Schiff base complexes with tetrahedral structures and their ligands in theoretical level; (2) To calculate the second-order NLO properties of Schiff base complexes with organometallic group being viewed as electronic donor. (3) To calculate the evolutions of second-order NLO properties of Schiff base complexes with exchanging the positions of the donors and acceptors.My thesis mainly consists of the following aspects: the first section is the review of the theoretical foundation of the study on the NLO property of organic and metal complex, the research approach and research development. The second section discussed the electronic structure and second-order NLO property of the tetrahedral structural Schiff base Co(II) complexes. The third section calculated the geometrical structure and second-order NLO properties of Schiff base complexes with organometallic group as electronic donor. Based on the geometrical structures and molecular orbitals and second-order NLO properties, the role of the Ni2+ in those metal complexes has been discussed. The fourth section analyzes the relation between second-order NLO properties of Schiff base and the positions of donors and acceptors. This calculation offers a new scheme to design the large second-order NLO responsesThe DFT B3LYP method has been employed, in order to analyze the second-order NLO properties of Schiff base complexes. The results of our studies in this thesis are: 1. The studies of the second-order NLO properties of open shell Co(II) metal complexes are shown that the second-order NLO properties of the metal complexes do not change obviously when compared with their ligands, the reason is that the NLO responses of Co(II) metal complexes is strongly related to intraligand charge transfer(ILCT) transitions. According to the frontier molecular orbitals, the less contributions of Co2+ in determining the NLO responses of metal complexes arises from the action of the bridging place in CT processes. 2. A series of Nickel(II) Schiff base complexes with organomettallic group as a new electronic donor. The results are shown that Ni2+ ion enhances the second-order NLO responses of the complexes because of the decreasing the occupied orbtials→unoccupied orbitals gaps, and increasing the electronic density distribution of coordinated atoms and adjacent carbon atoms in the conjugate chain. 3. A series of mono Schiff-base M(II) (M=Ni, Pd, Pt) complexes based on the crystal data are designed. DFT B3LYP method was employed to investigate the second-order nonlinear optical (NLO) properties of all metal complexes. The results show that the second-order NLO properties of metal complexes are intensively sensitive to the exchange of donor/acceptor because of the differences of the extent of charge separation and the ILCT processes. The metal ions do not offer direct contributions to second-order NLO responses because they are just electron bridges for transferring electrons in CT processes.