Thermally Activated Delayed Fluorescence (Green) in Undoped Film and Exciplex Emission (Blue) in Acridone–Carbazole Derivatives for OLEDs

Abstract

Donor–acceptor–donor materials (1,2) having acridone as acceptor unit and carbazole as donor were synthesized for optoelectronic applications. Carbazole was substituted on 2,7 positions of acridone in 1, while 3,6-trifluoromethylphenyl carbazole was substituted in 2. Steady-state and time-dependent emission properties of these compounds were studied in detail to get insight into their possible thermally activated delayed fluorescence (TADF) behavior. The singlet–triplet energy gap (ΔEST) was found to be as low as 0.17 eV (1) and 0.15 eV (2), favorable for TADF materials. Both these materials were found to be efficient green TADF emitters in organic light-emitting diode (OLED) devices. Interestingly, the TADF properties were observed for the first time in undoped 1,2-based devices, i.e., without host matrix, unlike the most commonly reported TADF emitters. Furthermore, an exciplex emission at 465 nm was observed in the blends of 1,2 with poly(vinylcarbazole) (PVK) in 1:7 (w/w) ratio. OLEDs with the blend o...