Regulating the Distance Between Donor and Acceptor in Space-Confined Through-Space Charge Transfer Emitters for Fast Radiative Decays and High-Efficiency Organic Light-Emitting Diodes With Low Efficiency Roll-Offs

作者：Song, Yongjun; Li, Yibo; Yu, Renyou; Zhang, Ke; He, Lei^*

来源：Advanced Optical Materials, 2023, 11(18).

DOI：10.1002/adom.202300432

• donor-acceptor distance
• organic light-emitting diode
• space-confined
• thermally activated delayed fluorescence
• through-space charge transfer

Through-space charge transfer (TSCT) emitters featuring thermally-activated delayed fluorescence (TADF) are extensively researched but suffer from low radiative decay rates (k(r,s)) due to insufficient through-space donor/acceptor interactions. Here, space-confined TSCT TADF emitters 1-3 with a chemically fixed benzophenone acceptor and a triphenylamine donor on different bridges, that is, 1-methyl-9,10-dihydroanthracene for 1, 4-methyl-9H-xanthene for 2 and 4-methyl-9H-thioxanthene for 3, which exhibit reinforced donor/acceptor interactions with shortened donor-acceptor distances, are reported. It is unveiled that there exists an optimal distance between the fixing sites of donor and acceptor. The emitter 2 with such an optimal distance shows both strong donor/acceptor interactions and high molecular rigidity, whereas the emitter 3 with a too short distance exhibits a twisted molecular structure and increased non-radiative deactivation. In solution, 1-3 shows high k(r,s) up to 3.0 x 10(7) s(-1). In doped films, 1-3 exhibits green emission with high k(r,s) up to 8.3 x 10(6) s(-1) and photoluminescent efficiency up to 0.96. Organic light-emitting diodes based on 1-3 afford high external quantum efficiencies up to 23.1% and largely alleviated efficiency roll-offs. The work demonstrates that using rigid bridges that render an optimal donor-acceptor distance is crucial to the development of highly efficient TSCT emitters with fast radiative decays for electroluminescence applications.