Extended -Conjugation Toward Efficient Orange Purely Organic Phosphorescence OLEDs

In purely organic room-temperature phosphorescence (RTP) materials, fluorescence radiative transitions generally compete against inter-system crossing (ISC) transitions to give fluorescence/phosphorescence dual emission. In order to achieve pure phosphorescence in RTP organic light-emitting diodes (OLEDs), extended pi-conjugation is introduced into Se-containing donors to suppress the fluorescence radiative transitions by the symmetry excited state orbitals in the introduced pi-pi* transitions that cancel the overlap of the orbitals, and two novel nonaromatic amine donor containing orange RTP emitters namely 2-(benzo[c]phenoxaselenin-10-yl)-4,6-diphenyl-1,3,5-triazine (BPXSeDRZ) and 2-(dibenzo[a,c]phenoxaselenin-11-yl)-4,6-diphenyl-1,3,5-triazine (DBPXSeDRZ) are developed, both of which exhibit efficient orange pure phosphorescence in doped films thanks to the sufficient ISC transitions. As a result, high external quantum efficiencies of 17.2% and 17.9% are respectively achieved for the orange RTP-OLEDs based on BPXSeDRZ and DBPXSeDRZ for the first time, and they also exhibit stable pure electro-phosphorescence spectra in a wide driving voltage. Moreover, by adopting DBPXSeDRZ as a sensitizer to harvest the triplet excitons and tetraphenyldibenzoperiflanthene as a conventional fluorescent emitter, the external quantum efficiency of the sensitized red fluorescent OLED can be elevated to 10.1%, which greatly expands the potential applications of the metal-free phosphors in OLEDs. By simply extending the pi-conjugations of the Se-containing nonaromatic amine donor with extra pi-pi* transitions, the fluorescence radiations that compete against inter-system crossing (ISC) can be suppressed resulting in metal-free room-temperature phosphorescence (RTP) emitters that demonstrate nearly unity ISC efficiencies. Adopting the developed emitters, efficient orange RTP organic light-emitting diodes are achieved for the first time with stable pure electro-phosphorescence.image