Here, γ, ηr and ηout are the charge carrier balance, the emissive exciton production efficiency and light outcoupling efficiency, respectively. Assuming that 4PZXPh-[10]CPP is a conventional fluorescence material, and γ, ηr and ηout are unity, 0.25 and 0.2, respectively, considering that ΦPL is 0.29, the experimental EQEMAX is close the ηext. Even for the OLED using 4PXZPh-[10]CPP:PyD2 emitting layer, which showed much longer photoluminescence lifetime, the EQEmax was 0.04% (Figure ). Although the device performance is below satisfactory, this is the first report of an electroluminescent device employing a donor-acceptor CPP-based emitter material.