Single-component polyfluorene electrolytes bearing different counterions for white light-emitting electrochemical cells

A series of polyfluorene (PF) electrolytes bearing Br^-, BF4-, or PF6- counterions were synthesized and characterized. 2,1,3-Benzoselenadiazole moieties were incorporated into polymer main chains to produce single-component white light-emitting polymers. The thermal stability of Br-containing ionic PF was decreased because of the Hofmann elimination occurred at higher temperature. By replacing Br^- with BF4- or PF6- counterions, the thermal stability of polymers was significantly improved. UV-vis absorption and photoluminescence spectra revealed that Br-containing ionic PF generates blue shift in methanol, while BF₄ and PF₆-containing ionic PFs show blue shift in acetonitrile. Electrochemical analysis revealed that oxidation potentials of BF₄ and PF₆-containing ionic PFs were decreased, resulting in increase in HOMO and LUMO levels. The optimized spin-coated light-emitting electrochemical cell (LEC) with the configuration of ITO/PEDOT/polymer/Ag showed a maximum luminescence efficiency of 1.56 lm/W at a low operation bias of 3 V. The single-component LEC device exhibited pure white light emission with CIE'1931 coordinates approaching (0.33, 0.33) and high color rendering index (CRI > 85), referring to its potential use in solid-state-lighting application.