四苯基卟啉和锌四苯基卟啉光谱的理论研究

Theoretical Investigation on the Spectrum of Tetraphenylporphyrin and Znic Tetraphenylporphyrin

采用TD-ωB97X/6-31G(d,p)方法在B3LYP/6-31G(d,p)优化得到的基态几何构型上计算了四苯基卟啉和锌四苯基卟啉的吸收光谱。计算表明四苯基卟啉和锌四苯基卟啉的吸收光谱分为Q_(x),Q_(y),B_(x)和B_(y)带,且激发态组态都主要是由两个单电子跃迁构成。其中B_(x)和B_(y)带十分接近,模拟光谱只出现一个B带的吸收峰。B带的吸收强度远远大于Q带,与前线轨道的节点和组态系数的正负有关。四苯基卟啉的HOMO-1和LUMO的轨道节点相似,HOMO和LUMO+1的轨道节点相似。B_(x)带的组态0.53Φ(H-1→L)+0.44Φ(H→L+1)吸收较强,而Q_(x)的组态系数一个是正值一个是负值,相互抵消,吸收较弱。虽然锌四苯基卟啉的Q_(x)和Q_(y)的重合,但吸收峰仍然比四苯基卟啉的吸收峰弱。

The TD-ωB97X/6-31G(d,p)method was used to calculate the absorption spectra of Tetraphenylporphyrin and Znictetraphenylporphyrin which were optimized at the B3LYP/6-31G(d,p)level of theory.All the absorption bands of Q_(x),Q_(y),B_(x)and B_(y) are consisted of two one-electron transitions configuration.The calculated B_(x)and B_(y)bands are closed and the experimental B band is contemplated as a superposition of B_(x)and B_(y)bands.The absorption intensity of B band is bigger than that of Q band.The absorption intensity is determined by the orbital nodes and configuration coefficients.The node character of HOMO of tetraphenylporphyrinis is similar to LUMO+1and the node character of HOMO-1is similar to LUMO.The absorption intensity of B_(x)band is strong since it is corresponding to electron transitions from HOMO to LUMO+1and from HOMO-1to LUMO.And both configuration coefficients are positive.The absorption intensity of Q_(x) band is weak since one of configuration coefficients is positive and the other is minus.Though the absorption wavelength of Q_(x)band of Znic tetraphenylporphyrin is superposed with the Q_(y)band,the absorption intensity of Q band of Znic tetraphenylporphyrin is weaker than that of Tetraphenylporphyrin.