Zheng Xue-Lian, Zheng Qizheng, Yang Cui-Cui, Tian Wei Quan
College of Chemistry and Chemical Engineering, Mianyang Teachers' College, Mianyang 621000, PR China.
Chongqing Key Laboratory of Chemical Theory and Mechanism, College of Chemistry and Chemical Engineering, Chongqing University, Huxi Campus, Chongqing 401331, PR China.
Spectrochim Acta A Mol Biomol Spectrosc. 2024 Dec 15;323:124890. doi: 10.1016/j.saa.2024.124890. Epub 2024 Jul 28.
Porphyrins are widely used as potential nonlinear optical (NLO) materials because of their highly delocalized π electrons and feasible synthesis and functionalization with broad biological applications. A variety of linear and cyclic porphyrin derivatives have been synthesized, and the correlation between their structures and NLO properties awaits being disclosed. In this work, the electronic structures and third-order NLO properties of linear and cyclic butadiyne-linked zinc porphyrin oligomers have been studied by quantum chemical methods and sum-over-states model. The static second hyperpolarizability (<γ>) increases exponentially with the number of zinc porphyrin units ([<γ>] = 0.67[<γ>]n, n = 2 ∼ 6) in linear π-conjugated oligomers, and the <γ> of the linear hexamer is about 74 times that of the monomer. Such enhancement of <γ> in linear oligomers originates from closely-lying frontier molecular orbitals available for low energy electron excitations and strong charge transfer-based excitations across porphyrins. The <γ>s of cyclic porphyrins are lower than that of the linear hexamer, though the interaction between the ring and the ligand enhances the <γ> of some cyclic zinc porphyrin complexes. The large two-photon absorption cross sections confer on these zinc porphyrin derivatives excellent candidates for two-photon absorption applications.
