An unsymmetrical perylene diester imide (PEI ST ), with flexible chains connected through imide and ester functionalities, was prepared through microwave-assisted synthesis. This compound displayed a remarkable fluorescence quantum yield of 87% and an exceptional performance in a host−guest OLED prepared by doping in CBP at 0.5 wt % concentration, providing an EQE max of 5.4% complemented by a brightness of 4265 cd/m 2 .