Synthesis And Properties Of Nonlinear Optical Crystals And Birefringent Crystals Containing π-Conjugated Units

Nonlinear optical crystal materials can greatly expand the wavelength range of solid-state lasers through frequency conversion,and thus have important applications in laser communication,photolithography and photoelectron spectroscopy.Birefringent crystal materials are widely used in optical isolators,phase compensators and circulators because they can effectively regulate polarized light.Becauseπ-conjugated functional groups can produce good nonlinear optical properties and large birefringence,they have attracted extensive attention from researchers.In this paper,a series of novel nonlinear optical crystals and birefringent crystal materials were synthesized based onπ-conjugated functional groups.The main research contents are as follows:1.Synthesis and characterization of Y[N（CN）₂]₄[NH（C₂H₅）₃]·3H₂O nonlinear optical material containing N（CN）₂^-.In this chapter,a non-centrosymmetric Y[N（CN）₂]₄[NH（C₂H₅）₃]·3H₂O containing N（CN）₂^-unit was synthesized by simple solution method.In its crystal structure,each Y³⁺shares comers with five N（CN）₂^-anions and three lattice water molecules,which,which,further form the one-dimensional（1D）chain structure by,which is finally stacked to form a three-dimensional structure through weak hydrogen bond connection between chains.The experimental results show that the compound can be transparent to 250 nm.The second harmonic generation experiment showed that second harmonic generation response of the compound was about 2.8 times of KH₂PO₄.Theoretical calculations show that the optical properties of the compound are mainly determined byπ-conjugated N（CN）₂^-anionic groups.This work shows thatπ-conjugated N（CN）₂^-anionic groups is an excellent new nonlinear optical functional group.2.Synthesis and characterization of C₃N₆H₈SbI₅·H₂O perovskite nonlinear optical crystal.In this work,we successfully synthesized noncentrosymmetric C₃N₆H₈SbI₅·H₂O by solution method by introducingπ-conjugated melamine.C₃N₆H₈SbI₅·H₂O crystallizes in the Pna2₁ space group,and its crystal structure is composed of one Sb⁵⁺coordinating with six I^-to form a twisted SbI₆ octahedron.By sharing I^-,two adjacent octahedra form a one-dimensional perovskite-like chain structure.The experimental results show that the absorption edge of the compound is 576 nm.The results of the second harmonic generation experiment show that the compound has strong second harmonic generation response.Theoretical calculations show thatπ-conjugated melamine and Sb⁵⁺cations are the main contributors to the optical properties of the compound.3.Synthesis and characterization of C₃N₆H₈Br₂ halide birefringent crystal.In this work,we still focused onπ-conjugated melamine units and obtained a centrosymmetric compound C₃N₆H₈Br₂ containing melamine cations by the solution method.In the crystal structure,the arrangement of[H₈C₃N₆]²⁺is completely parallel.Experiment results show that the birefringence of C₃N₆H₈Br₂ is 0.11@550 nm,which is basically consistent with the theoretical simulation value of 0.13@550 nm.The theoretical calculation shows that the optical properties of the compound are mainly derived from the C and N atoms of melamine cations and the synergistic effect with Br.