Efficient Blue and Yellow Organic Light-Emitting Diodes Enabled by Aggregation-Induced Emission

A new class of donor–bridge–acceptor (D−π–A) π-conjugated light-emitting molecules comprising carbazole as donor and maleimide ( Cbz-MI, Cbz-MI(d) ), phthalimide ( Cbz-Pth ) as acceptor units with phenyl ring as spacer have been synthesized in good yields. These compounds exhibit high quantum yield with three distinct emission colors yellowish-green ( Cbz-MI ), bright yellow Cbz-MI(d), and sky blue ( Cbz-Pth ) in the solid state. Single-crystal X-ray and quantum chemical calculations reveals that twisting of the phenyl rings with high torsional angle on maleimide and phthalimide units reduce the effective inter-chromophore electronic coupling, furnish dramatic changes in their photophysical properties in solution and solid states. Intriguingly, Cbz-MI(d) and Cbz-Pth exhibits a unique aggregation-induced blue-shifted emission (AIBSE) due to restricted intramolecular rotation (RIR) process, while Cbz-MI shows red-shifted emission in the solid state. The solvatochromic study reveal that combined RIR and excited state migration augment AIE (aggregation-induced emission) properties. The electrochemical properties reveal that Cbz-MI exhibits high oxidation propensity while Cbz-Pth shows low reduction values. Subsequently, organic light-emitting diodes (OLEDs) were fabricated with a simple three-layer device containing Cbz-Pth and Cbz-MI(d) as emitting layers. Cbz-MI(d) exhibits high performance yellow OLED with an external quantum efficiency exceeding ∼4.1% and a brightness exceeding ∼73915 cd/m 2, which is among the best performance reported for bright yellow fluorescence organic light-emitting diodes.