Organic–Inorganic Hybrids Composed of Keggin-Type [PMo<sub>10</sub>V<sub>2</sub>O<sub>40</sub>]<sup>5–</sup> Anions and Porphyrins: The Synthesis, Characterization, and Influence of Porphyrin Substituents on Optical Nonlinearities
Farooq Khurum Shehzad, Arshad Iqbal, Yunshan Zhou, Lijuan Zhang, Ting Wang, Xiaoyu Ren
Abstract
In order to understand the influence of porphyrin substituents on the nonlinear optical properties of organic–inorganic hybrids composed of an anionic metal–oxygen cluster and a porphyrin cation, porphyrins bearing different functional groups (4-pyridyl, 4-hydroxyphenyl, and 3,4-dimethoxyphenyl) were chosen as prototypes to react with the well-known Keggin-type polyanion α-[PMo10V2O40]5–, which acted as an electron acceptor; this led to formation of three electrostatically bonded disalts with formal formulas of [C40H28N8][H4PMo10V2O40]2 (1), [C44H32N4O4][H4PMo10V2O40]2 (2), and [C52H48N4O8][H4PMo10V2O40]2 (3), respectively. These hybrids were systematically characterized by a variety of means. The nonlinear optical properties of these compounds were studied using the Z-scan technique, conducted with irradiation at λ = 532 nm with a 6 ns duration and a repetition rate of 10 Hz at focus E0 = 4.2 μJ. While all the hybrids showed an enhanced NLO response compared to their corresponding mother porphyrins, they also exhibited reverse saturation absorption, self-defocusing performance, and an enhancement of the second hyperpolarizability value γ in the order of γ(1) < γ(2) < γ(3), which is parallel to the electron- or charge-donor ability of the functional groups on the porphyrin. Namely, the greater the electron-donor ability of functional groups on the porphyrin, the greater the NLO response.