Exploration of high-performance triptycene-based thermally activated delayed fluorescence materials via structural alteration of donor fragment

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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 (Δ E 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 Δ E ST value decreases and λ em is red-shifted for the molecules using the same acceptor units. Analogously, the 1 CT‒ 3 CT state splitting (Δ E 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 Δ E 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 Δ E ST , and the smaller λ h for PPXZ-QNX(CN)2 make it the best candidate among all the designed molecules.