Uncovering the Aggregation-Induced Emission Mechanisms of Phenoxazine and Phenothiazine Groups.

Molecules with both aggregation-induced emission (AIE) and thermally activated delayed fluorescence (TADF) properties are potential organic light-emitting diode materials; however, the AIE and TADF mechanisms are still debatable. In this work, four molecules incorporating carbazole (), phenoxazine (), and phenothiazine () as donor groups to the diphenylsulfone acceptor were investigated. The experiment results indicate that a molecule containing exhibits solely TADF properties, whereas molecules containing and demonstrate both TADF and AIE characteristics. As for , the result indicates that the thin-film environment restricts molecular twisting, consequently reducing nonradiative decay, thereby attributing to the AIE property by density functional theory and molecular dynamics simulation. As for , the result suggests that the restricted access to a conical intersection in a singlet excited via an expansion in the C-S-C angle is the pivotal factor for the AIE characteristic. The C-S-C angle twist of is impeded in the aggregate state and resulted in luminescence. Understanding the mechanisms serves as a valuable guide for the development of new AIE systems, enabling their application in various practical domains.