Woon, K.-L.K.-L.WoonYi, C.-L.C.-L.YiPan, K.-C.K.-C.PanEtherington, M.K.M.K.EtheringtonCHUNG-CHIH WUKEN-TSUNG WONGMonkman, A.P.A.P.Monkman2020-06-112020-06-11201919327447https://scholars.lib.ntu.edu.tw/handle/123456789/498114Understanding 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 reorganization, giving rise to multiple charge-transfer excited states. As a result of such a reorganization, the TRZ and TPA moieties become cofacially aligned, driven by a strong dipole-dipole attraction between the TPA and TRZ units, forming a weakly charge-transfer dimer state, in stark contrast to the case of PXZ-TPA-TRZ where the rigid PXZ bridge only supports a single PXZ-TRZ charge transfer (CT) state. The low-energy TPA-TRZ dimer is found to have a high-energy dimer local triplet state, which quenches delayed emission because the resultant singlet CT local triplet energy gap is too large to mediate efficient reverse intersystem crossing. However, organic light-emitting diodes using PXZ-TPA-TRZ as an emitting dopant resulted in external quantum efficiency as high as 22%, more than two times higher than that of DMAC-TPA-TRZ-based device, showing the impact that such intramolecular reorganization and donor-acceptor dimerization have on TADF performance. © 2019 American Chemical Society.Charge transfer; Conformations; Dimerization; Dimers; Fluorescence; Molecules; Organic light emitting diodes (OLED); Synthesis (chemical); Charge transfer state; Conformational relaxation; Dipole-dipole attractions; Emissive molecules; Excited-state dynamics; External quantum efficiency; Inter-system crossings; Thermally activated delayed fluorescences; Excited statesjournal article10.1021/acs.jpcc.9b019002-s2.0-85065893103https://www.scopus.com/inward/record.uri?eid=2-s2.0-85065893103&doi=10.1021%2facs.jpcc.9b01900&partnerID=40&md5=0b3b163f07e87dc529aaef1c54e619f6