Poly(alkyl thiophene-3-carboxylates). Synthesis, properties and electroluminescence studies of a polythiophene with a carbonyl group attached to the ring

Improved synthetic methodology for poly(hexyl and octyl thiophene-3-carboxylates) (la and lb) is reported. n = 6700 and 9400 (Mw/Mn = 2.5 and 3.2), λmax for fluorescence emission = 600 and 610 nm and for electroluminescence = 600 and 615 nm, for la and lb respectively. The 1H NMR spectra showed more aromatic peaks than can be explained using triads, and it is suggested that pentads, involving longer range influences, must be considered to explain the spectra. Electroluminescence efficiencies of ca. 0.02% were observed for devices made from la and b. A bilayer device of ITO/poly(3-octylthiophene)/lb/Al emitted at 646 nm, where poly(3-octylthiophene) emits. The efficiency was low but was an order of magnitude greater than for poly(3-octylthiophene) itself.