Selenoxanthen-9-one-based emitters exhibiting efficient room temperature phosphorescence for electroluminescent and oxygen sensing applications

Two selenoxanthen-9-one-based emitters (Se-2DPA and Se-2TPA) were synthesized by introducing diphenylamine and triphenylamine as electron donors. The doped films of Se-2DPA and Se-2TPA exhibited bright fluorescence-phosphorescence dual emission and comparable photoluminescence quantum yields (ΦPL) of 31.4 % and 29.6 %, respectively. Unlike the Se-2DPA with phosphorescence lifetime of 1.1 ms, Se-2TPA shows significantly extended phosphorescence lifetime up to 17.7 ms. As revealed by computational and experimental investigations, Se-2DPA maintained more effective spin orbit coupling (SOC) between T1 and S0 states and its radiative rate constant of phosphorescence is 1 order of magnitude higher than that of Se-2TPA, which resulted in a relatively shorter phosphorescence lifetime. Consequently, solution-processed organic light-emitting diodes (OLEDs) based on Se-2DPA with shorter phosphorescence lifetime achieved a maximum external quantum efficiency of 8.8 %, which is much higher than the device based on Se-2TPA (only 0.8 %). In contrast, Se-2TPA showed higher sensitivity for oxygen sensing and the Stern-Volmer quenching constant (KSV) value reached 3.04 × 10−3 ppm owing to the longer phosphorescence lifetime, which is over 3-folds higher than that of Se-2DPA (8.88 × 10−4 ppm) under the same conditions.