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.