Enhancing Light-Emitting Efficiency of Blue Through-Space Charge Transfer Emitters via Fixing Configuration Induced by Intramolecular Hydrogen Bonding

Closely
aligned configuration of the donor (D) and acceptor (A)
is crucial for the light-emitting efficiency of thermally activated
delayed fluorescence (TADF) materials with through-space charge transfer
(TSCT) characteristics. However, precisely controlling the D–A
distance of blue TSCT-TADF emitters is still challenging. Herein,
an extra donor (D*) located on the side of the primary donor (D) is
introduced to construct the hydrogen bonding with A and thus modulate
the distance of D and A units to prepare high-efficiency blue TSCT
emitters. The obtained “V”-shaped TSCT emitter presents
a minimal D–A distance of 2.890 Å with a highly parallel
D–A configuration. As a result, a high rate of radiative decay
(>107 s–1) and photoluminescence quantum
yield (nearly 90%) are achieved. The corresponding blue organic light-emitting
diodes show maximum external quantum efficiencies (EQEmax) of 27.9% with a Commission Internationale de L’Eclairage
(CIE) coordinate of (0.16, 0.21), which is the highest device efficiency
of fluorene-based blue TSCT-TADF emitters. In addition, the TSCT-TADF
emitter-sensitized OLEDs also achieve a high EQEmax of
29.3% with a CIE coordinate of (0.12, 0.16) and a narrow emission.