Molecular Conformational Isomerization: An Efficient Way to Design Novel Emitters with Dual-Thermally Activated Delayed Fluorescence Characteristics and Their Optoelectronic and Bioimaging Applications

Single-molecule luminophores with dual-thermally activated delayed fluorescence (TADF) properties are receiving increasing attention. However, how to achieve these goals requires more in-depth studies. Herein, we demonstrate a novel example emitter, 10-(5-(2-(pyridin-3-yl)-[4,5 & PRIME;-bipyrimidin]-6-yl)pyridin-2-yl)-10H-phenoxazine (PmPy-PXZ), enabling dual-TADF properties due to its key feature of conformational isomeri-zation. Introducing a pyridine bridge can greatly reduce the steric hindrance and facilitate dual-stable conformations in the ground state, where the quasi-axial (QA) forms predominate. Moreover, unlike previ-ously reported TADF molecules with dual confirmations, both theoretical and experimental measurements show that not only the quasi-equatorial (QE) forms but also the QA forms exhibit distinct TADF character-istics, which can be attributed to an additional higher reverse intersystem crossing pathway. This is the first time that dual-TADF properties of single molecules have been achieved based on conformational isomerism. Its applications in "self-doping" organic light-emitting diode and biomedical imaging have further been investigated. All these results show the good potential of such dual-band TADF emitters based on molecular conformational isomerization.