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

Abstract

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 (>10 7 s −1 ) and photoluminescence quantum yield (nearly 90%) are achieved. The corresponding blue organic light-emitting diodes show maximum external quantum efficiencies (EQE max ) 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 EQE max of 29.3% with a CIE coordinate of (0.12, 0.16) and a narrow emission.

Intramolecular Hydrogen Bonding Rigidifying Flexible Bridge for Solution- and Vacuum-Processed TSCT-TADF Emitters

“…Ren et al. recently introduced N···H intramolecular hydrogen bonds (IHBs) into TSCT-TADF system, successfully adjusted the relative orientation between D/A units, and realized efficient TSCT-TADF luminescence . Although the effect of hydrogen bonding on the luminescence properties of TADF emitters is still controversial, , its potential in regulating the molecular configuration of TADF emitters has been widely recognized.…”