氢卟啉和镁卟啉分子溶剂效应的理论研究

Theoretical Study on the Solvent Effect of Porphyrin and Magnesium Porphyrin Molecules

采用溶剂场极化连续模型在密度泛函B3LYP/6-31G(D)水平上研究了氢卟啉和镁卟啉分子在四氢呋喃(THF)、二甲基亚砜(DMSO)、二氯甲烷(CH2Cl2)、氯仿(CHCl3)这四种不同极性的溶剂环境中的几何结构和分子轨道能级,从而研究了溶剂效应引起的分子几何构型和轨道能级的变化.然后采用上述溶剂环境下优化的几何结构在含时密度泛函水平上计算了它们的激发能、吸收波长、跃迁组成和振荡强度.理论计算结果表明,对比真空条件下的氢卟啉和镁卟啉分子的几何结构,溶剂场中两种卟啉分子的几何结构都发生了微弱的变化,这种变化随溶剂介电常数的增大而有所增强.计算结果表明溶剂环境中氢卟啉和镁卟啉分子的电子吸收光谱发生了普遍的红移,结合分子轨道理论对这种变化给出了可能的解释.在此基础上,对这种包含溶剂效应的理论分析方法用于检验卟啉类化合物作为染料敏化太阳能电池光敏剂的可行性作了进一步的探讨。

The solvent polarized continuum model on the basis of the density functional B3LYP/6-31G（D） level was used to study the molecular geometrical structures and orbital energy levels of porphyrin and magnesium porphyrin in the solvents with different polarities such as tetrahydrofuran, dimethysulfoxide, dichloromethane, chloroform, and further the variation of the molecular structure and orbital energy level caused by the solvent effect. The geometrical structures optimized in the solvents above on the time dependent density functional level were then used to calculate the excitation energy, absorption wavelength, oscillator strength and the orbital composition of the electronic transition. According to the calculation resuits, compared with the geometrical structures of porphyrin and magnesium porphyrin molecules in the vacuum state, the molecular geometrical structures have a little variation in all the solvents considered, which becomes stronger along with the increase in the dielectric constants of the solvents. It was also found that the absorption wavelengths of porphyrin and magnesium porphyrin had the general red shift. The molecular orbital theory was used to give a possible explanation for this variation, and the feasibility of using the theoretical analysis involving solvent effect to check the possibility of porphyrin compounds as a photosensitizer of dye-sensitized solar cells was also discussed.