In Situ Absorption Spectra and ESR Measurements of Poly(trans-(2,2′-bithiophene-5-yl)-(2,2′:5′,2′′-terthiophene-5-yl)ethylene) During Electrochemical Doping

Abstract

The electrochemical, optical and magnetic properties of poly( trans -(2,2 ′ -bithiophene-5-yl)-(2,2 ′ :5 ′ ,2 ′′ -terthiophene-5-yl)ethylene), PBTTTE, during electrochemical p -type doping have been investigated in comparison with those of poly( trans -bis(thiophene-2-yl)ethylene), trans -PTE, by cyclic voltammetry, in situ optical absorption spectra, and electron spin resonance (ESR) measurements. The band gap energy of PBTTTE was evaluated to be 2.0 eV and about 0.1 eV larger than that of trans -PTE. This result can be interpreted in terms of a change in the torsion angle between neighboring thiophene rings. The spin susceptibility determied by ESR measurements increased from 2.4×10 -8 to 4.4×10 -6 emu/mol upon doping and then decreased slightly. Changes in optical absorption spectra and ESR spectra suggest the formation of polaron and/or bipolaron upon doping. The spin density evaluated from the spin susceptibility was inconsistent with the dopant density. That is, even at lightly doped state the newly...