Aggregation-induced emission, mechanochromism and blue electroluminescence of carbazole and triphenylamine-substituted ethenes

Carbazole and triphenylamine-substituted ethenes are synthesized [Ph ₂CCPh(R), R = 9-carbazolyl, 9-hexyl-3-carbazolyl and 4-(diphenylamino)phenyl] and their optical properties are investigated. All luminogens are nonemissive when molecularly dissolved in good solvents but become highly emissive in the aggregated state, showing a phenomenon of aggregation-induced emission. High solid-state fluorescence quantum yields up to 97.6% have been achieved in their solid thin films. The luminogens are thermally stable, showing high degradation temperatures of up to 315 °C. They exhibit mechanochromism: their emissions can be repeatedly switched between blue and green colors by simple grinding-fuming and grinding-heating processes due to the morphological change from crystalline to amorphous state and vice versa. Multilayer light-emitting diodes with device configurations of ITO/NPB/dye/TPBi/Alq₃/LiF/Al, ITO/NPB/dye/TPBi/LiF/Al and ITO/dye/TPBi/LiF/Al are fabricated, which emit sky blue light with maximum luminance, current efficiency, power efficiency and external quantum efficiency of 11700 cd m^-2, 7.5 cd A^-1, 7.9 lm W^-1 and 3.3%, respectively.