Intramolecular Dimerization Quenching of Delayed Emission in Asymmetric D-D’-A TADF Emitters

Understanding the excited-state dynamics and conformational relaxation in thermally-activated delayed fluorescence (TADF) molecules, including conformations that potentially support intramolecular through-space charge transfer, can open new avenues for TADF molecular design as well as elucidate complex photophysical pathways in structurally complex molecules. Emissive molecules comprising a donor (triphenylamine, TPA) and an acceptor (triphenyltriazine, TRZ) bridged by a second donor (9,9 dimethyl-9-10-dihydroacridin, DMAC or phenoxazine, PXZ) are synthesized and characterized. In solution, the flexibility of the sp3-hybridized carbon atom in DMAC of DMAC-TPA-TRZ, compared to the rigid PXZ, allows significant conformational reorganisation giving rise to multiple charge-transfer excited states. As a result of such reorganization, the TRZ and TPA moieties become co-facially aligned, driven by strong dipole-dipole attraction between the TPA and TRZ units, forming a weakly charge transfer dimer state, in star...