A 3D electropolymerized thin film based on an isoporphyrin and on a pyridine end-decorated molybdenum(II) halide cluster: Photoelectrochemical and impedance properties

Abstract

Herein, the first example of formation of a 3D hybrid organic-inorganic copolymer based on an isoporphyrin and on a pyridine end-decorated molybdenum(II) halide cluster. The isoporphyrin copolymer thin film was obtained by electropolymerization of zinc-5,15-bis(p-tolyl)porphyrin in the presence of polyiodometalate with 6 pendant pyridyl ligands (((Bu4N)2[{Mo6I8}(OOC-C5H4N)6]). Electrogenerated porphyrin radical cation is a powerful electrophile which can rapidly react with the pyridine end-decorated Mo(II) halide cluster as nucleophile to form 3D copolymer containing stable isoporphyrin.The electropolymerization was monitored by electrochemical quartz crystal microbalance (EQCM). The copolymer was characterized by UV-Vis-NIR spectroscopy, X-ray photoelectron spectroscopy (XPS), electrochemistry, and atomic force microscopy (AFM). The existence of the radical of the isoporphyrin copolymer was proved by electron spin resonance spectroscopy (EPR).Interestingly, the UV-Vis-NIR spectra of the copolymer exhibited broadening and splitting of the Soret band as well as one additional band in the NIR between 750 nm and 1000 nm.The photoelectrochemical properties have been studied by electrochemical impedance spectroscopy and by photocurrent transient measurements under visible-NIR light irradiation.The 3D copolymer containing stable isoporphyrin radical exhibits interesting photocurrent response even under only NIR illumination.In the solid state, the 3D copolymer could be stored for over several months and even one year without any degradation under ambient conditions in air.