A Tetraphenylbenzene-Based AIE Luminogen with Donor-Acceptor Structure: Unique Mechanochromic Emission and High Exciton Utilization

Luminogens featuring aggregation-induced emission characteristics (AIEgens) have been widely applied in high-performance non-doped blue organic light-emitting diodes (OLEDs). However, AIEgens with high exciton utilization are rare. Herein, a tetraphenylbenzene (TPB)-based AIEgen of PXZ-TPB-CN, in which phenoxazine (PXZ) and cyano (CN) serve as strong electron-donating and withdrawing group, respectively, was rationally designed and facilely synthesized. PXZ-TPB-CN exhibits a unique mechanochromic luminescence. The lifetime of its ground powders and films exhibits a new decay component compared with the pristine powders, which attributes to the reverse intersystem crossing from the high-lying triplet state process according to the theoretical calculation. To further verify this process, a non-doped OLED using PXZ-TPB-CN as emitting layer was fabricated, and a much higher maximum external quantum efficiency (EQE) of the device than that of theoretical one was obtained, suggesting that triplet excitons are involved in a radiative process. In addition, the high horizontally oriented dipoles also contribute to this high EQE. This work provides a new strategy to realize blue AIEgen-based OLEDs with high exciton utilization by attaching strong donors and acceptors on twisted AIE cores.