V-shaped thiophene-based oligomers with improved electroluminescence properties

The synthesis via the Stille coupling of a new family of oligomers derived from benzo[b]thiophene is reported. Owing to their branched molecular structure lacking any symmetry element, these compounds display a low tendency to crystallization and better film-forming properties than their linear counterparts. Spin-coated films show photoluminescence efficiencies up to 50%. Light-emitting diodes with spin-coated films as the active layers display markedly improved performance with respect to similar devices based on linear oligothiophenes, with luminance values up to more than 10 000 cd m(-2). Semiempirical PM3 and ZINDO/S calculations provide insight into the molecular geometries and electron distribution of the frontier orbitals of the new compounds. Cyclic voltammetry data indicates that the transformation of the thienyl sulfur of benzo[b]thiophene to the corresponding thienyl-SS-dioxide leads an increase in electron affinity by 0.5-0.7 V, analogous to that of the corresponding linear oligomers.