Poly(3-methylthiophene)-coated electrodes: optical and electrical properties as a function of redox potential and amplification of electrical and chemical signals using poly(3-methylthiophene)-based microelectrochemical transistors

Abstract

Optical and electrical properties of anodically grown poly-3-methythiophene are reported as a function of redox potential in CH3CN/0.1M (n-Bu4N)ClO4. Poly-3-methylthiophene can be grown by the oxidation of 3-methylthiophene and deposited onto Au or Pt electrode surfaces. A pair of poly-3-methylthiophene-connected microelectrodes can function as a transistor where one of the electrodes is regarded as 'source' and the other as 'drain' with the source being referenced to the solution as a gate. The poly-3-methylthiophene is the analogue of the channel of a solid state field effect transistor, since its conductivity changes by 100,000,000 depending on the potential. Large optical (300-800 nm) and electrical changes for the poly-3-methylthiophene occur between approx. +0.3 V and approx. +0.8 V vs. SCE. The reduced material has an absorption maximum at 490 nm and the oxidized material has an absorption maximum at 750 nm. The optical density changes parallel the resistant changes that occur as the potential of the polymer changes between approx. +0.3 and approx. +0.8 V vs. SCE. The charging of a 1.5 micrometer thick film of poly-3-methylthiophene involves approx. 10,000 time more charge per unit of projected area then a smooth Pt electrode, consistent with a large effective internal surface area for the conducting polymer.