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 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 trend of photoluminescence quantum yield observed in solution and solid state was related to both a significant contribution of internal conversion in the deactivation process, in solution, and the formation of intra-chain hydrogen-bonds, due to the peculiar chain conformation, in solid state. LED devices showed the highest efficiency in the yellow region among similar copolymers containing both fluorene and 1,1-dioxothiophene functionalities.