Counter‐ion modulation: A facile approach toward quenching‐resistant multi‐resonance emitters for efficient narrowband electroluminescence

Abstract Different from previous quenching‐resistant multi‐resonance (MR) emitters using covalently‐bonded steric substituents, here we propose a facile strategy for developing quenching‐resistant MR emitters via modulating counter ions of carbocation‐doped polycyclic chromophores. It is found that by simply changing the counter ion through a quantitative ion‐exchange reaction to increase its size from 28.4 to 440.9 cm 3 /mol, the π‐stacking of corresponding polycyclic skeleton is distinctly weakened, giving much narrowed emission bands under high doping concentrations, and greatly improved photoluminescent quantum efficiency in solid‐state film. Solution‐processed organic light‐emitting diodes (OLEDs) based on the emitter containing a bulky tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate ( BArF 24 − ) counter ion reveal narrowband electroluminescence with full‐width at half maxima of 43 nm and maximum external quantum efficiency of 18.7%, greatly superior than that of emitter with small Cl − counter ion where no detectable electroluminescence signal is observed, shedding light on the potential of counter‐ion modulation on developing efficient ionic MR emitters for narrowband OLEDs.