Non-doped OLEDs based on tetraphenylethylene phenanthroimidazoles with negligible efficiency roll-off: effects of end group regulated stimulus responsive AIE luminogens

Abstract

The positional isomers of phenanthroimidazoles, TPE-NPPB and TPE-APPB, have been designed to understand the positional effects of triphenylamine (TPA) and tetraphenylethylene (TPE) units on the aggregation-induced emission and mechanochromism. The phenanthroimidazoles TPE-NPPB and TPE-APPB show reversible mechanochromism between blue and green colours and were analysed via powder X-ray diffraction (PXRD). The PXRD analysis reveals that the phase transition of TPE-NPPB and TPE-APPB from crystalline to amorphous state is associated with colour changes. The non-doped OLEDs based on TPE-NPPB and TPE-APPB exhibit high external quantum efficiency (EQE) of 3.2 and 5.3%, current efficiency (CE) of 4.32 and 5.28 cd A⁻¹ and power efficiency (PE) of 4.01 and 4.92 lm W⁻¹, respectively. The improvement of mechanochromic materials with aggregation-induced emission (AIE) behaviour play a vital role in optoelectronics.