Highly efficient green and blue emitters exhibiting thermally activated delayed fluorescence with 4,6-substituted dibenzo[b,d]thiophene-S,S-dioxide as electron acceptor and their electroluminescent properties

Through attaching electron donors to the 4, 6-positions of dibenzo[b,d]thiophene-S,S-dioxide (DBTDO), three organic emitters (SO-OZ, SO-AD and SO-CZ) with D-A-D configuration have been designed and synthesized. They not only show high thermal stability with decomposition temperature (T_d) higher than 460 °C, but also exhibit photoluminescent quantum yield (PLQY) as high as 0.9. Despite that SO-CZ with carbazole unit as electron donor cannot furnish thermally activated delayed fluorescence (TADF) emission, both SO-OZ with 10H-phenoxazine as electron donor and SO-AD bearing electron donor of 9,9-dimethylacridine exhibit typical TADF behaviors due to their small energy difference between S₁ and T₁ excited states (ΔE_ST). Critically, SO-OZ can show very fast revers intersystem crossing (RISC) process with rate constant of RISC (k_RISC) ca. 1.8 × 10⁶ s⁻¹. The cyclic voltammetry (CV) results indicate their decent electrochemical stability by showing reversible oxidation and reduction processes. When doped into the emission layer of organic light-emitting diodes (OLEDs), they can show good potential as highly efficient emitters, showing electroluminescent efficiencies of the maximum current efficiency (CE) of 53.4 cd A⁻¹, the maximum power efficiency (PE) of 52.4 lm W⁻¹ and the maximum external quantum efficiency (EQE) of 20.5 %. These encouraging results can provide critical information for developing highly efficient TADF emitters based on DBTDO electron acceptor.