Highly efficient deep-blue electrofluorescence with optimized excited state composition and "hot-exciton" channel.

The properties of excited states of emitters play an important role in OLEDs. How to obtain balanced hybrid localized charge transfer (HLCT) state by reasonably designing molecules is still a challenge. Herein, three HLCT states D-π-A type blue fluorophores with different LE/CT hybrid degree were designed and synthesized, namely 3,6-di-tert-butyl-9-(4-(6-(4-(4,5-diphenyl-4 H -1,2,4-triazol-3-yl)phenyl)pyren-1-yl)phenyl)-9 H carbazole (DTPCZPYTZ), 3,6-di-tert-butyl-9-(4-(4-(4-(4,5-diphenyl-4 H -1,2,4-triazol-3-yl)phenyl)naphthalen-1-yl)phenyl)-9 H -carbazole (DTPCZNATZ) and 3,6-di-tert-butyl-9-(4''-(4,5-diphenyl-4 H -1,2,4-triazol-3-yl)-[1,1':4′,1″-terphenyl]-4-yl)-9 H -carbazole (DTPCZPHTZ). DTPCZPHTZ achieved quasi-equivalent hybrid local and charge-transfer (HLCT) excited state and efficient "hot-exciton" channel, the non-doped deep-blue device based on DTPCZPHTZ has an electroluminescence emission peak (λ EL) of 427 nm with Commission International de L'Eclairage (CIE) of (0.157, 0.037), the maximum external quantum efficiency (EQE) is up to 5.7% and the efficiency roll-off is only 5% (under 1000 cd m−2), which is outstanding in the reported deep-blue emitters. This study proved that the quasi-equivalent hybrid HLCT state is beneficial to improving device performance. This work provides a flexible and convenient method for fine-tuning the excited states of emitters, by changing the number of benzene rings in the intermediate π bridge, the degree of LE/CT hybridization can be adjusted. Finally, quasi-equivalent hybrid deep-blue luminescent emitter and highly efficient non-doped deep-blue OLED is obtained. [Display omitted] • Construction of quasi-equivalent hybrid local and charge-transfer (HLCT) excited state and hot exciton channels. • Efficient non-doped deep-blue OLED with EQE up to 5.7% and CIE (0.157, 0.037). • Highly Suppressed efficiency roll-off of only 1%–5% at 1000 cd m−2. [ABSTRACT FROM AUTHOR]