Chalcogen‐Driven Conformational Control for Room‐Temperature Phosphorescence and Zn 2+ Coordination‐Induced Delayed Fluorescence in Phenazine Derivatives

ABSTRACT 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, Zn 2+ 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.