Aggregation-Induced Emission:  Effects of Molecular Structure, Solid-State Conformation, and Morphological Packing Arrangement on Light-Emitting Behaviors of Diphenyldibenzofulvene Derivatives

Propeller-shaped molecules diphenyldibenzofulvene (1) and (4-methoxyphenyl)phenyldibenzofulvene (2) were nonemissive when dissolved in good solvents but became luminescent when aggregated in poor solvents or in the solid state, showing a novel phenomenon of aggregation-induced emission (AIE). 8-Phenylbenzo[e]acephenanthrylene (3), a ring-closed form of 1 with one of its phenyl blades locked, was emissive in the solutions, suggesting that the AIE effects of 1 and 2 are caused by the restrictions of intramolecular rotations of their aromatic blades in the aggregation state. The crystals of 1 and 2 emitted stronger, bluer lights than their amorphous powders, possibly due to the structural rigidification and conformational twisting of the dye molecules in the crystalline phase. The light-emitting diodes with a device configuration of ITO/NPB/dye/BCP/Alq3/LiF/Al were fabricated, which emitted bluish-green and yellow lights with maximum luminance and current efficiency up to 5000 Cd/m2 and 1.90 Cd/A, respectively.