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

Abstract

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-4H-1,2,4-triazol-3-yl)phenyl)pyren-1-yl)phenyl)-9H carbazole (DTPCZPYTZ), 3,6-di-tert-butyl-9-(4-(4-(4-(4,5-diphenyl-4H-1,2,4-triazol-3-yl)phenyl)naphthalen-1-yl)phenyl)-9H-carbazole (DTPCZNATZ) and 3,6-di-tert-butyl-9-(4''-(4,5-diphenyl-4H-1,2,4-triazol-3-yl)-[1,1':4′,1″-terphenyl]-4-yl)-9H-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 (λEL) 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.