Thermally activated delayed fluorescence materials based on 3, 3′-position substituted bis(phenylsulfonyl)benzene

Two highly efficient thermally activated delayed fluorescent (TADF) materials with twisted donor-acceptor-donor (D-A-D) structure, DMACBB and PXZBB, have been designed and synthesized based on bis(phenylsulfonyl)benzene as the acceptor (A) and 9,9-dimethyl-9,10-dihydroacridine (DMAC) or phenoxazine (PXZ) as the donor (D). Attaching the donor to the 3, 3′-positions of bis(phenylsulfonyl)benzene obtains larger torsion angle between donor and acceptor as well as suitable ICT effects, which results in almost complete separation of their FMOs and limited overlap. Both emitters successfully achieve small ΔE_ST (≤0.2 eV), simultaneously exhibit high photoluminescence quantum yields (≥80%). Both of them possess distinct TADF features. The DMACBB-based device exhibits sky blue emission with the peak at 472 nm, while the PXZBB-based device shows slightly red-shifted and emits green light with the peak at 507 nm because of the stronger electron-donating ability of PXZ than that of DMAC. The TADF-OLED based on DMACBB achieves higher the maximum external quantum efficiency (EQE_max of 10.1%) than the TADF-OLED based on PXZBB (EQE_max of 8.2%) with the turn-on voltage of 3.5 V.