Engineering of aggregation-induced emission luminogens by isomeric strategy to achieve high-performance optoelectronic device

Achieving non-doped organic light-emitting diodes (OLEDs) with high electroluminescent (EL) performance is essential for both illumination source and display applications. A source of this difficulty is the aggregation-induce quenching effect of emitters in the solid state, which results in low EL efficiency and severe roll-off. Herein, four isomeric aggregation-induced emission luminogens (AIEgens), namely TPE-3Cz-mPBI, TPE-3Cz-pPBI, TPE-2Cz-mPBI, and TPE-2Cz-pPBI, are constructed by varying the linkage positions of electron-accepter 1,2-diphenyl-1H-benzo[dlimidazole (PBI), electron-donor carbazole, and ME-active triphenylethene functional groups. A comprehensive investigation is carried out, and the results indicate that position isomerism dramatically affects electronic structures, photophysical properties, carrier transport capabilities, and device performances. Compared with TPE-3Cz-mPBI and TPE-3Cz-pPBI, TPE-2Cz-mPBI, and TPE-2C2-pPBI exhibit more excellent AIE-active with the fluorescence quantum yield up to 72.5% and 89.7% in the neat films. Moreover, TPE-2Cz-mPBI shows high electron transport property and appropriate energy level, which favor balanced charge carrier injection/transporting in OLEDs. Hence, non-doped device based on TPE-2Cz-mPBI exhibits the best EL performance with external quantum efficiency, current efficiency, and power efficiency of 3.2%, 7.8 cd A(-1), and 7.7 lm W-1, respectively. The isomeric strategy presents a promising method to extend the structural diversity of highly efficient AIE emitters, optimize optoelectronic properties, and construct high-performance non-doped devices. Due to intrinsic twisted structure and accessible protonated N-electron in molecular framework, the isomers exhibit impressive mechanochromism and acidochromism.