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

Abstract

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 (ΔEST), emission wavelength (λem), and electron/hole reorganization energy (λe/λh) 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 ΔEST value decreases and λem is red-shifted for the molecules using the same acceptor units. Analogously, the 1CT‒3CT state splitting (ΔEST (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 ΔEST (CT) values (0.01–0.05 eV), has been accomplished by structural modification of the D-fragments. The greater electron-donating strength, the smaller ΔEST, and the smaller λh for PPXZ-QNX(CN)2 make it the best candidate among all the designed molecules.

Keywords

• Triptycenes
• Thermally activated delayed fluorescence
• Singlet-triplet energy gap
• Optimal Hartree-Fock
• Density functional theory
• Time-dependent density functional theory