Synthesis and optoelectronic properties of starlike polyfluorenes with a silsesquioxane core

A novel starlike polyfluorene derivative, PFO-SQ, was synthesized by the Ni(0)-catalyzed reaction of octa(2-(4-bromophenyl)ethyl)octasilsesquioxane (OBPE-SQ) and polydioctylfluoroene (PFO). The incorporation of the silsesquioxane core into polyfluorene could significantly reduce the aggregation as well as enhance the thermal stability. The DSC study showed an elimination of the glass transition and crystallization as well as a significant reduction of the melting enthalpy in PFO-SQ. The UV-vis absorption spectra in a different solvent combination or solid-state film showed an intensity reduction of the aggregation peak for PFO-SQ in comparison with that of PFO. The stability of the photoluminescence spectra of PFO-SQ could be up to 150 degreesC, while that of PFO showed a significant green emission at 530 nm. A single-layer LED device using PFO-SQ showed a turn on voltage of 6.0 V, a brightness of 5430 cd/m(2) (at a drive voltage of 8.8 V), and a current density of 0.844 A/cm(2). The maximum luminescence intensity and quantum efficiency of PFO-SQ were almost twice as good as those of the PFO electroluminescent device. Hence, the incorporation of the inorganic silsesquioxane core into polyfluorenes could provide a new methodology for preparing organic light-emitting diodes with improved thermal and optoelectronic characteristics.