Oxidation State Tuning of Room Temperature Phosphorescence and Delayed Fluorescence in Phenothiazine and Phenothiazine-5,5-dioxide Dimers.

Heterocyclic dimers consisting of combinations of butterfly-shaped phenothiazine (PTZ) and its chemically oxidized form phenothiazine-5,5-dioxide (PTZ(SO )) have been synthesized. A twist is imposed across the dimers by ortho-substituents including methyl ethers, sulfides and sulfones. X-ray crystallography, cyclic voltammetry and optical spectroscopy, underpinned by computational studies, have been employed to study the interplay between the oxidation state, conformational restriction, and emission mechanisms including thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP). While the PTZ(SO ) dimers are simple fluorophores, the presence of PTZ induces triplet-mediated emission with a mixed PTZ-PTZ(SO ) dimer displaying concentration dependent hallmarks of both TADF and RTP.