Efficient donor-acceptor-donor borylated compounds with extremely small Delta E-ST for thermally activated delayed fluorescence OLEDs

Borane-based complexes have attracted considerable attention as thermally activated delayed fluorescence (TADF) emitters because of their thermal stability, high fluorescence efficiency, and favourable carrier mobility. In this work, we provide a facile way for borylated compounds to enable the spatially adjacent electron donor and acceptor groups to form a near-orthogonal configuration, generating an extremely small energy gap between triplet and singlet excited states (Delta E-ST, similar to 30 meV). We demonstrate here a new series of donor-acceptor-donor borylated compounds using functional acridan derivatives as the electron donors and dimesitylborane as the acceptor moieties, which easily generates an intramolecular charge transfer upon excitation. All compounds achieved strong TADF emission and were used as dopants to fabricate TADF OLEDs. Yellow-emitting devices A and B yielded maximum efficiencies of 7.6% (22.2 cd/A) and 10.1% (32.2 cd/A), respectively. Moreover, the green-emitting device C achieved a maximum efficiency of 19.3% (56.8 cd/A) and subsequently dropped to 18.2% (53.6 cd/A) at luminance levels of 102 cd/m(2). Overall, the high electroluminescent (EL) efficiencies, together with mitigated efficiency roll-off, illustrate that these compounds have a high potential for EL applications.