氨基酸桥联手性双卟啉的二阶非线性光学性质研究

采用半经验量子化学PM3方法对系列氨基酸桥联双卟啉1, 2, 3, 4及其锌配合物进行了几何结构优化, 并用TDHF/PM3方法计算了其静态二阶非线性光学系数. 计算结果表明, L型-氨基酸桥联双卟啉及其锌配合物具有右手螺旋结构特征. 在电偶极近似下, 不同手性氨基酸侧链基团R对分子的总体二阶非线性光学系数β和βHRS的影响不大, 但对二阶非线性光学系数的手性分量βxyz却有显著影响. βxyz与螺旋结构参数r2ζ/L4成正比关系, 符合手性分子二阶非线性光学响应的单电子螺旋模型理论. β张量分析表明, 此类分子表现为以八极为主、 偶极为辅的多极分子, 卟啉环与锌离子的配位有利于增加二阶非线性光学响应的偶极分量和手性分量βxyz.

Investigation on Second-order Nonlinear Optical Property of Amino Acid Bridged Chiral Porphyrin Dimmer

Geometries of amino acid bridged bis-porphyrin 1,2,3,4 and their zinc(Ⅱ) complexes were optimized at semiempirical PM3 quantum chemistry level. Static second-order NLO coefficients of these bis-porphyrins were then calculated by TDHF/PM3 method. The calculation results show that all L-type amino acid bridged bis-porphyrins exhibit right-handed helix structures. Within the electric-dipole approximation, second-order NLO coefficients β of these bis-porphyrins change little with the varying of amino acid side chains. However, the second-order NLO chiral components βxyz of amino acid bridged bis-porphyrins are significantly different. The chiral component βxyz and the helix structure parameter r2ζ/L4 matches βxyz∝r2ζ/L4, indicating the second-order chiral NLO response of helix chiral bis-porphyrins could be well described by one-electron helical model theory. The analysis of β components indicates that these amino acid bridged bis-porphyrins are multipolar molecules with ‖βJ=3‖/‖βJ=1‖≈11—17. In comparison to free-base helix bis-porphyrin, the insertion of Zn(Ⅱ) ion favors the accretion of the second-order NLO dipolar component and chiral component βxyz of molecules.