In situ FTIR study of charge conduction in a poly(3-methylthiophene)–poly({1-[2-(3-thienyl)ethyl]-1,4,8,11-tetraazacyclotetradecane}nickel(II) perchlorate) copolymer film

Abstract

We have used in situ FTIR spectroscopy to examine the effect of incorporating redox-active pendant [Ni(tetraazamacrocycle)]²⁺ moieties in poly(3-methylthiophene)(PMT). Experiments were performed on Pt electrodes modified with PMT, and PMT-copoly-{1-[2-(3-thienyl)ethyl]-1,4,8,11-tetraazacyclotetradecane}nicke(II) perchlorate (PMT–P1) in acetonitrile–0.2 mol l^–1 tetraethylammonium tetrafluoroborate. Inspection of the IR activated vibration (IRAV) region of the spectrum (1000–1600 cm^–1) of PMT shows that oxidation occurs with three distinct regions of behaviour with increasing potential. There is a changeover in the carrier type being generated between the first two regions, probably from polaron to bipolaron. The evolution of the electronic band (1600–6000 cm^–1), due to a charge carrier transition, suggests a relatively uniform conjugation length in this polymer. That the copolymer backbone posesses mobile charges is shown by the observation of IRAVs in its spectra, at similar energies to those observed for other thiophene-based polymers. However, the electronic band of the copolymer is at lower energy than for PMT, and its position changes significantly with potential. This is related to the increase in static relative permittivity of PMT–P1 compared with PMT owing to the ion content of the neutral copolymer film. Neutral PMT films appear to contain very little solvent, whereas neutral PMT–P1 films contain significant quantities, possibly associated with the [Ni(macrocycle)]²⁺ moieties.