The molecular geometries, electronic structures, and excitation energies of tin and lead phthalocyanine compounds, SnPc, PbPc, Sn(Pc)2, and Pb(Pc)2, were investigated using the B3LYP method within a framework of density functional theory (DFT). The geometries of SnPc, PbPc, Sn(Pc)2, and Pb(Pc)2 were optimized under C4v, C4v, D4d, and D4d molecular symmetries, respectively. The excitation energies of these molecules were computed by the time-dependent DFT (TD-DFT) method. The calculated results for the excited states of three compounds other than the unknown Pb(Pc)2 corresponded well with the experimental results of electronic absorption spectroscopy. The non-planar C4v molecular structure of SnPc and PbPc influences especially on the orbital energy of the HOMO−1 through mixing of the s-type atomic orbital of the central metal atom to the π system of the Pc ring in an anti-bonding way; however, the HOMO and the LUMO have little effect of the deviation from the planar structure because they have no contribution from the atomic orbital of the central metal. This orbital mixing pushes up the orbital energy of the HOMO−1, and reduces the energy of the metal-to-ligand charge transfer band of SnPc and PbPc. The calculated results also reproduced well the excitation profile of Sn(Pc)2, which was quite different from that of SnPc. The strong interactions between the π-type orbitals of two Pc moieties altered the electronic structure resulting in the characteristic excitation profile of Sn(Pc)2. In addition, this caused a reduction of about 0.8 eV in the ionization potential as compared to usual MPcs including SnPc, which was consistent with the experimental results.
在密度泛函理论(DFT)框架内,采用 B3LYP 方法研究了
锡和
铅酞菁化合物 SnPc、PbPc、Sn(Pc)2 和 Pb(Pc)2 的分子几何结构、电子结构和激发能。在 C4v、C4v、
D4d 和
D4d 分子对称性下分别优化了 SnPc、PbPc、Sn(Pc)2 和 Pb(Pc)2 的几何结构。这些分子的激发态能量是通过时间相关 DFT(TD-DFT)方法计算得出的。除未知的 Pb(Pc)2 外,其他三种化合物激发态的计算结果与电子吸收光谱的实验结果非常吻合。SnPc 和 PbPc 的非平面 C4v 分子结构通过中心
金属原子的 s 型原子轨道以反键方式与 Pc 环的π系混合,对 HOMO-1 的轨道能产生了特别的影响;然而,由于 HOMO 和 LUMO 没有中心
金属原子轨道的贡献,它们对平面结构的偏离影响很小。这种轨道混合推高了 HOMO-1 的轨道能量,降低了 SnPc 和 PbPc 的
金属-
配体电荷转移带的能量。计算结果也很好地再现了 Sn(Pc)2 的激发曲线,该曲线与 SnPc 的激发曲线截然不同。两个 Pc 分子的 π 型轨道之间的强相互作用改变了电子结构,从而产生了 Sn(Pc)2 的特征激发曲线。 此外,与包括 SnPc 在内的普通 MPcs 相比,这导致电离电位降低了约 0.8 eV,这与实验结果一致。