Strategic molecular design of efficient solution- and vacuum-processable deep-red thermally activated delayed fluorescence emitters featuring remarkable color saturation

Herein, we address the scarcity of efficient molecular designs for deep-red thermally activated delayed fluorescence (TADF) emitters that can be used in both solution- and vacuum-processed organic light-emitting diodes (OLEDs). The majority of red TADF emitters reported to date contain a rigid acceptor unit limiting solubility and hindering their application in solution-processed OLEDs. To overcome this challenge, we introduce a novel TADF emitter, 2,3-bis(4-(bis(4-(tert-butyl)phenyl)amino)phenyl)-6,7-bis(4-(tert-butyl)phenyl)quinoxaline-5,8-dicarbonitrile (tBuTPAQxCN). The molecular design features a twisted donor–acceptor architecture with hydrogen bonding between donor and acceptor units, resulting in a small singlet–triplet energy gap (0.11 eV), high photoluminescence quantum yield of (>99 %), and a short-delayed fluorescence lifetime (5.5 µs). The incorporation of a quinoxaline acceptor unit decorated with peripheral t-butylphenyl groups and a t-butyl-protected triphenylamine donor units proved to be effective for improving solubility and minimizing intermolecular interactions. The fabricated solution-processed OLEDs based on tBuTPAQxCN show external quantum efficiencies (EQEs) of up to 10.3 % and a pure-red emission peak at 662 nm. Furthermore, the vacuum-processed OLEDs based on tBuTPAQxCN show EQEs of up to 20.5 %. Notably, the solution-processed OLEDs exhibit excellent color saturation, with CIE(x,y) coordinates of (0.67, 0.32), precisely matching the national television standard committee (NTSC) prescribed coordinates of (0.67, 0.33).