Tailored Near‐Infrared Luminescent Materials with Fast Reverse Intersystem Crossing for Efficient Deep‐Red/Near‐Infrared Organic Light‐Emitting Diodes with High Efficiencies and Small Roll‐Offs

Abstract

AbstractRobust organic luminescent materials radiating deep‐red/near‐infrared (DR/NIR) light are highly desired in organic light‐emitting diodes (OLEDs). However, most reported DR/NIR materials show only moderate electroluminescence (EL) efficiencies accompanied by rock‐ribbed efficiency roll‐offs, which immensely limit their practical use in OLEDs. In this work, two tailor‐made NIR luminescent materials with thermally activated delayed fluorescence (TADF) property are developed based on rigid and strong electron‐accepting core of 2,7‐bis(4‐cyanophenyl)dibenzo[a,c]phenazine‐11,12‐dicarbonitrile and electron donors of triphenylamine or N,N‐di([1,1′‐biphenyl]‐4‐yl)phenylamine. They exhibit high photoluminescence quantum yields, fast reverse intersystem crossing processes and large horizontal dipole ratios. Their nondoped OLEDs show NIR lights with maximum external quantum efficiencies (ηext,maxS) of 0.59% at 856 nm and 1.14% at 850 nm. And their doped OLEDs radiate DR to NIR lights (646–737 nm) and attain superb ηext,maxs of up to 30.3% at 646 nm with small efficiency roll‐offs. The state‐of‐the‐art EL performances of both NIR TADF materials demonstrate their high potential as emitters in OLEDs and the insights gained in this work will enlighten the further development of efficient NIR luminescent materials.