Synthesis of a novel fluorescent and ion sensitive monomer bearing quinoxaline moieties and its electropolymerization

A novel terthienyl based fluorescent polymer bearing pendant quinoxaline moieties directly attached to the 3-positions of the central thiophene ring was synthesized by electrochemical polymerization of 4-((2,5-dithiophen-2-yl)thiophen-3-yl)pyrrolo[1,2-a]quinoxaline ( TT-Q). The corresponding polymer was characterized by cyclic voltammetry, FT-IR and UV–vis spectroscopy. The polymer exhibits a reversible redox behavior (Ep 1/2 = 1.05 V) accompanied with a reversible electrochromic behavior; yellowish orange in the neutral state and green in the oxidized state. Band gap of polymer was found ( E g = 1.94 eV). Moreover, the sensitivity of both the monomer and its polymer towards metal cations was investigated by monitoring the change in the fluorescence intensity. Among various common ions, both the monomer and its polymer were found to be selective towards Fe 3+ ions by quenching the fluorescence efficiency with a Stern–Volmer constant ( K sv) of (2.7 × 10 3 M −1) and (5.0 × 10 3 M −1) for monomer and polymer solutions, respectively.