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

Abstract

Carbazole and triphenylamine-substituted ethenes are synthesized [Ph₂CCPh(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 11 700 cd m⁻², 7.5 cd A⁻¹, 7.9 lm W⁻¹ and 3.3%, respectively.