Tailoring structural rigidity utilizing a lock/unlock donor strategy for highly efficient solution processed blue and green HLCT OLEDs

Highly efficient solution-processed HLCT OLEDs based on aromatic carbonyls are rarely reported, especially blue ones. In this pursuit, based on a twisted acceptor core, we designed and synthesized two unsymmetrical keto-carbonitrile emitters, namely, KCPhCz and KCPhDPA , utilizing a locked (carbazole) and unlocked (diphenylamine) donor strategy exhibiting color tunability. Additionally, we found that the insertion of a π-linker between the donor and acceptor converted an inefficient TADF emitter (KCCz, previously reported) into an efficient blue HLCT emitter ( KCPhCz ). We found this efficiency enhancement based on a weak carbazole donor was due to HLCT characteristics. KCPhCz and KCPhDPA -based molecules emitted in the blue and green regions respectively. Non-doped devices based on KCPhCz and KCPhDPA exhibited EQEs of 5.7 and 7.4%, respectively. The best performance was demonstrated by 7.5 wt% doped devices from both emitters. The KCPhDPA -based device showed a PE max of 39.2 lm W −1 , a CE max of 49.8 cd A −1 , and an EQE max of 15.3% at a brightness of 100 cd m −2 with CIE of (0.34, 0.58) and EL λ max at 532 nm. In contrast, the KCPhCz -based optimized device showed a PE max of 22.7 lm W −1 , a CE max of 32.5 cd A −1 , and an EQE max of 10.8% at a brightness of 100 cd m −2 in the blue region with CIE of (0.18, 0.19) where EL showed λ max at 480 nm. Highly efficient solution-processed HLCT OLEDs based on aromatic carbonyls have rarely been reported. Based on a twisted acceptor core, we developed and synthesized two highly efficient unsymmetrical keto-carbonitrile HLCT emitters for OLEDs.