Chalcogen-Driven Conformational Control for Room-Temperature Phosphorescence and Zn2+ Coordination-Induced Delayed Fluorescence in Phenazine Derivatives.

Purely organic luminescent materials are pivotal for optoelectronics, with chalcogen-fused phenazines serving as basic building blocks owing to their strong electron donating ability and enhanced spin-orbit coupling effect. However, a systematic understanding of how the chalcogen identity governs intrinsic conformational preference between quasi-axial (QA) and quasi-equatorial (QE) forms remains elusive. To address this, we designed a series of derivatives featuring phenoxazine, phenothiazine, and phenoselenazine donors coupled with a terpyridine acceptor. We demonstrate that the chalcogen atom dictates molecular conformation: phenoxazine derivative exclusively adopts the QE conformation, phenothiazine derivative predominantly favors QE, while phenoselenazine derivative stabilizes in the QA form. Notably, heating induces a phase transition in polymorphs toward their thermodynamically favored conformations. Furthermore, Zn2+ coordination enhances intramolecular charge transfer (ICT) strength, shifting the thermodynamically preferred conformation and triggering a switch from room-temperature phosphorescence (RTP) to dual RTP-delayed fluorescence (DF) emission. This work validates the chalcogen-determined conformation and ICT strength can effectively modulates DF/RTP performance, deepening the fundamental understanding of the chalcogen-mediated conformation and properties for the rational design of organic luminescent materials.