Donor‐Void‐Acceptor Type TADF Emitters with Asymmetric Donors for Highly Efficient Deep Blue OLEDs

Abstract Two asymmetric donor‐acceptor‐donor’ (D‐A‐D’) type deep blue thermally activated delayed fluorescence (TADF) emitters, namely PAO‐1 and PAO‐2, are developed with highly rigid 10‐(pyridin‐2‐yl)acridin‐9(10 H )‐one (PAO) as acceptor (A). PAO is characterized by the 3,6‐sites carbon atoms that are void to its own HOMO and the deeper HOMO‐2 of PAO acceptor rather than its HOMO is involved in the HOMO of the TADF emitters. Such D‐void‐A connecting mode favors to lower the molecular HOMO and generate short‐wavelength fluorescence by enlarging the bandgap of the TADF emitters. Two different carbazole donors are utilized in the asymmetric D‐A‐D’ type emitters, which not only keep the deep blue emission but also enhance the oscillator strength ( f ) for faster radiative transition rates ( k r s > 10 8 s −1 ) and slightly slow the intersystem crossing (ISC) rates ( k ISC s) and reverse ISC ( k RISC s) than the symmetric PAO‐0, which can reduce exciton trap in the conversion cycles between singlet and triplet excitons. The deep blue OLEDs of PAO‐1 and PAO‐2 exhibit external quantum efficiencies (EQEs) of 32.5% and 30.1% with CIE (0.15, 0.10) and (0.15, 0.11) and low‐efficiency roll‐offs. These findings provide a design strategy for developing highly efficient deep‐blue TADF emitters.