Multipurpose heavy atom effects for organic solution room temperature-phosphorescence

Abstract Heavy atom insertions are often used to increase spin–orbit coupling to enhance the performance of advanced emissive molecules. In this work we apply heavy atoms in both the linker (thiophene) and donor (phenoselenazine) groups of D-A emitters, and compare these to triazine-based reference emitters that show thermally activated delayed fluorescence (TADF). While the thiophene groups provide a lower-energy triplet state suitable for room temperature phosphorescence (RTP), the additional inclusion of Se allows the corresponding PSe-ThZ material to undergo RTP even in solution (sRTP). Despite having similar separation of singlet and triplet energies, much weaker sRTP activity in a phenoxazine-substituted emitter without the Se atom shows the utility of this approach, but also that inclusion of cooperative heavy atoms can detract from TADF performance.