1 research outputs found
Thermally Activated Delayed Fluorescent Emitters Based on Cyanobenzene Exhibiting Fast Reverse Intersystem Crossing to Suppress the Efficiency Roll-Off
Thermally
activated delayed fluorescent (TADF) materials exhibiting
the fast reverse intersystem crossing (RISC) process are essential
for improving the stability of organic light-emitting diodes (OLEDs).
However, for most TADF emitters, the upconversion processes from
the lowest triplet state (T1) to the lowest singlet state
(S1) are still inefficient due to the low RISC (kRISC) rate below 105 s–1. Herein, we report two TADF molecules, 2DACz-mCN and 2DACz-oCN, that possess multiple donor units to minimize singlet–triplet
energy splitting (ΔEST) and enhance the spin–orbit coupling matrix elements.
Our work shows that the rate constants of RISC of 2DACz-mCN and 2DACz-oCN are
as fast as ∼2.7 × 106 and ∼8.6 ×
106 s–1, which are 1 order of magnitude
higher than the other benzonitrile-based TADF molecules. The short
delayed fluorescent lifetimes of ∼1.58 and ∼1.16 μs
in doped films are achieved. The OLEDs by utilizing 2DACz-oCN as emitter exhibit green electroluminescence
(EL) with CIE chromaticity coordinates of (0.28, 0.49) and high maximum
quantum efficiency of ∼25.1% with the suppressed efficiency
roll-off, which still remains ∼21% at the luminance of 1000
cd/m2