Electroluminescent poly(fluorene-co-thiophene-S, S-dioxide):: synthesis, characterisation and structure-property relationships

A new copolymer, constituted by the regular alternation of a fluorene derivative with a 1,1-dioxothiophene moiety, has been synthesised via Suzuki coupling. The molecular, thermal, structural, and photophysical characterisations have been performed. The material showed two dimensional order, enhanced by annealing; molecular modelling calculations afforded a consistent structural model accounting for the optical data. In comparison with both polyfluorenes and 1,1-dioxothiophene oligomers the unusual photoluminescence quantum yields observed in solution and in the solid state can be related to a significant contribution of internal conversion to the deactivation process in solution, and the formation of intra-chain hydrogen-bonds, due to a peculiar chain conformation, in the solid state. LED devices based on this new copolymer showed the highest efficiency compared with similar copolymers containing both fluorene and 1,1-dioxothiophene functionalities.