Efficient Yellow Thermally Activated Delayed Fluorescent Emitters Based on 3,5-Dicyanopyridine Acceptors

Thermally activated delayed fluorescent (TADF) emitters have been extensively investigated in the past decade. Compared to the prosperous development of the donor unit, the development of an efficient acceptor with easy modulation still remains insufficient. In this contribution, 3,5-dicyanopyridine substituted with naphthyl and thienyl groups is applied as an acceptor for constructing efficient TADF compounds. Two molecules named 4-(4-(10H-phenoxazin-10-yl)phenyl)-2,6-di(naphthalen-1-yl)pyridine-3,5-dicarbonitrile (NP) and 4-(4-(10H-phenoxazin-10-yl)phenyl)-2,6-di(thiophen-2-yl)pyridine-3,5-dicarbonitrile (TP) are designed and synthesized. Theoretical simulation and photophysical characterization suggest both emitters possess small energy differences between the lowest singlet and triplet excited states, benefiting from the rational combination of acceptors with the 10H-phenoxazine (PXZ) donor through twisted donor-acceptor design and hence establishing efficient TADF processes featuring a short delayed lifetime of 0.65 μs for NP and 0.80 μs for TP. With careful selection of carrier transporting layers, high external quantum efficiencies (EQEs) of 17.1% for NP and 12.4% for TP are achieved.