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 (ΔE ST ) 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 of 1,2 with PVK as the active layer showed an intense electroluminescence at 465 nm matching well with the exciplex photoluminescence. Thus, we show that acridone−carbazole derivatives (1,2) offer variable electroluminescence as undoped TADF green emitter and blue exciplex emitter when doped in PVK.

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Materials showing white light emission have found applications in a variety of solid state devices especially in display technology. For white light emission, doping of red (R), green (G) and blue (B) emitters in a host matrix is commonly practised. However, finding RGB emitters of similar stability with homogenous doping is challenging. Furthermore, such devices suffer from color purity in the long run. Small organic light emitters, capable of colour tuning and having a broad emission spectrum are in high demand as they provide colour stability, reproducibility, a simple device geometry and high efficiency. Recently, it has been shown that the efficiency of OLEDs can be enhanced by employing thermally activated delayed fluorescence (TADF) materials. Here, we designed and synthesised a xanthone-carbazole based D-A-D material (Xan-Cbz) for TADF properties. Blue TADF emission, in neat thin films, at 470 nm was observed and further investigated by studying delayed fluorescence and lifetime measurements. In addition, a blend of Xan-Cbz with NPD shows exciplex emission at 525 nm in thin film. OLEDs based on Xan-Cbz were fabricated using several device configurations. OLEDs having the device configuration ITO/PEDOT:PSS/NPD/Xan-Cbz/Bphen/LiF-Al showed a luminance of 1.96 Â 10 4 Cd m À2 (at a current density of 50 mA cm À2 ) and V ON at $6 V. Electroluminescence showed the features of both neat emission (470 nm) of Xan-Cbz and its exciplex (525 nm) with NPD. Further, colour tuning was observed as a function of applied voltage and the ratio of light intensity (I 525 /I 470 ) of neat and exciplex emission was found to decrease with increasing voltage. Greenish-blue emission (CIE coordinates: 0.202, 0.382) from Xan-Cbz OLEDs was obtained. Xan-Cbz showed its neat emission (at 470 nm) in ITO/PEDOT:PSS/ CBP/Xan-Cbz/Bphen/LiF-Al and pure exciplex emission (at 525 nm) in ITO/PEDOT:PSS/NPD:Xan-Cbz/ Bphen/LiF-Al device configurations. Thus in this article we showed blue TADF emission, exciplex emission and voltage dependent color tuning in OLEDs based on a small organic emitter.