Effects of donor position and multiple charge transfer pathways in asymmetric pyridyl-sulfonyl TADF emitters

We have designed and synthesized a pair of highly asymmetric D-aA-D′ type pyridyl-sulfonyl based isomers comprising phenothiazine (PTZ) carbazole (Cz) donor units, which are able to emit thermally activated delayed fluorescence. PTZ-pS4-Py-2Cz PTZ-mS4-Py-2Cz both possess spatial separation HOMO/LUMO on the acceptor moieties, resulting in small calculated singlet–triplet energy gaps (~0.25 eV). Both exhibit dual emission, is attributed charge transfer states associated with Cz PTZ moieties at higher lower energies, respectively. Photoluminescence quantum yields time-resolved emission decays show significant differences for two isomers, para- isomer exhibiting more efficient stronger fluorescence than meta- – strong contrast recently reported analogous Cz-Cz D-aA-D isomers. The findings clearly that interconversion triplets via rISC mechanism promoted when parallel allowed interact, explaining improved performance Cz-PTZ materials compared previous ones. Finally, moderate device was achieved warm-yellowish (CIE; 0.41; 0.53 & 0.49; 0.48) non-doped OLEDs, exhibited 0.5% 1.9% maximum external efficiencies