Blue fluorophores comprised of tetraphenylethene and imidazole: aggregation-induced emission and electroluminescence

By melting tetraphenylethene (TPE) and 1,2,4,5-tetraphenyl-1H-imidazole (TPI) units together through different linking positions, three new fluorophores are synthesized, and their optical, electronic and electroluminescence (EL) properties are fully studied. Owing to the presence of TPE unit(s), these fluorophores are weak emitters in solutions, but are induced to emit strongly in the aggregated state, presenting typical aggregation-induced emission characteristics. The experimental and computational results reveal that different connection patterns between TPE and TPI could impact the molecular conjugation greatly, leading to varied emission wavelength, fluorescence quantum yield and EL performance in organic light emitting diodes (OLEDs). The fluorophore built by attaching TPE unit to the 1-position of imidazole ring shows bluest fluorescence, and its EL device emits at deep blue region (445 nm; CIE = (0.16, 0.15)). And the device based on the fluorophore by linking TPE to the 2- position of imidazole ring shows EL at 467 nm (CIE = (0.17, 0.22)) with good efficiencies of 3.17 cd∙A–1, and 1.77%.