氮混杂金属卟啉吸收光谱性质的理论研究

采用密度泛函理论在B3LYP/6-31+G(d)水平上研究了4种金属Mg, Ni, Cu, Zn配位的自由卟啉(FBP)及氮混杂卟啉(NECP)的几何结构及分子轨道能级. 采用含时密度泛函理论(TD-DFT)方法计算了金属与2种卟啉配位后在气体条件下的电子吸收光谱, 包括激发能、 吸收波长、 跃迁组成和振子强度.计算结果表明, 与金属配位的FBP(M-FBP)具有D_4h对称性, 分子轨道能级HOMO/HOMO-1和LUMO/LUMO+1因能级相近发生简并, HOMO-LUMO轨道能级差大约3.0 eV, 在Soret带出现较强吸收峰.由于C/N原子位置的改变, 非对称性结构的M-NECP前线轨道组成发生改变, 轨道能级差(HOMO-LUMO)减小至2.6 eV左右, 且能级发生分裂, Soret带出现多个电子吸收谱峰, Q带也出现吸收峰. 本文研究了水、 氯仿和苯3种不同极性溶剂对M-FBP和M-NECP的分子轨道及电子吸收光谱的影响, 结果表明, 随溶剂极性减弱金属配合物的电子吸收光谱发生红移, 并且吸收峰强度增强.

Theoritical Studies on the Structure and Absorption Spectra of Neo-Confused Metal Porphyrin†

On the basis of detailed density functional theory(DFT), the molecular geometrical structures and orbital energy levels of free base porphyrin(FBP) and neo-confused porphyrin(NECP) coordinated with Mg, Ni, Cu, Zn were studied at B3LYP/6-31+G(d) level. The electronic absorption spectra of metal coordinated porphyrins were studied in gas phase at time dependent density functional level, including the excitation energy, absorption wavelength, oscillator strength and the orbital composition of the electronic transition. Since the metal coordinated FBPs(M-FBP) have D_4h symmetry, HOMO/HOMO-1, LUMO/LUMO+1 degenerate respectively with the similar orbital energy level. The energy gaps of HOMO-LUMO of M-FBPs are about 3.0 eV. The structure and orbital properties of M-FBPs evolve strong Soret bands in the absorption spectra. Due to the change of C/N atom in the center structure of NECP, M-NECP molecular frontier orbitals composition is more complicated than that of M-FBP. In M-NECPs, the molecular orbital energy gaps(HOMO-LUMO) reduce to about 2.6 eV. The C/N exchange strategy can vary the molecular symmetry and molecular orbital composition of M-NECPs, which leads to the energy level splitting, strong electronic absorption peaks of Soret band and the appearance of Q absorption band. All the parameters of M-FBPs and M-NECPs were investigated in three different solvents(water, chloroform and benzene). Under the solvent conditions, the electronic absorption spectra of M-FBP and M-NECP take place red shift along with the weaken polarity of solvent(water, chloroform, benzene) and enhance the absorption peak intensity.