Stable isoporphyrin copolymer: Electrochemical mechanism and behavior and photovoltaic properties

Abstract

Two types of porphyrin copolymer thin films were obtained by electropolymerization of zinc-5,15-bis(p-tolyl)porphyrin. Electrogenerated porphyrin radical cation and dication are powerful electrophiles which can rapidly react with 1,1″-(1,3-propanediyl)bis-4,4′-bipyridinium hexafluorophosphate salt (bpy+–(CH2)3–+bpy·2PF6−) as nucleophiles to form copolymers containing stable isoporphyrin radicals or porphyrins, depending of the applied upper potential limit (1.0 V versus 1.6 V). Electrochemical routes leading to these electroactive copolymers are discussed and the unusual redox properties of copolymers containing stable isoporphyrin radicals are studied. The electropolymerization of the two copolymers was monitored by electrochemical quartz crystal microbalance (EQCM). The copolymers were characterized by UV–Vis–NIR spectroscopy, X-ray photoelectron spectroscopy (XPS), electrochemistry, electron spin resonance (ESR) and atomic force microscopy (AFM). Their electrical properties have been studied by electrochemical impedance spectroscopy and their photovoltaic performances have been investigated by photocurrent transient measurements under visible-NIR light irradiation. The isoporphyrin radical copolymer exhibited considerably better photocurrent generation when compared to the porphyrin copolymer.