Exploration of high-performance triptycene-based thermally activated delayed fluorescence materials via structural...

The utilization of thermally activated delayed fluorescence (TADF) materials in highly proficient organic light-emitting diodes (OLEDs) has attracted much attention. Based on TADF material TPA-QNX(CN)2, a series of three-dimensional donor-acceptor (D-A) triptycenes have been designed via structural modification of D-fragment. The influences of different D-fragments with various electron-donating strengths on the singlet-triplet energy gap (ΔE_ST), emission wavelength (λ_em), and electron/hole reorganization energy (λ_e/λ_h) are extensively studied by applying density functional theory (DFT) coupled with time-dependent density functional theory (TD-DFT). The computed results imply that as the electron-donating strength of the D-fragments increases, the ΔE_ST value decreases and λ_em is red-shifted for the molecules using the same acceptor units. Analogously, the ¹CT‒³CT state splitting (ΔE_ST (CT)) is also decreased by enlarging the twist angle (β) between the phenyl ring and alternative D-fragment. Therefore, efficient color tuning within a broad emission range (434-610 nm), as well as small ΔE_ST (CT) values (0.01-0.05 eV), has been accomplished by structural modification of the D-fragments. The greater electron-donating strength, the smaller ΔE_ST, and the smaller λ_h for PPXZ-QNX(CN)2 make it the best candidate among all the designed molecules.