Synthesis and structure–property correlation of blue fluorescence isomer emitters based on rigid pyrazine-bridged carbazole frameworks†
Three novel blue fluorescence isomer emitters, namely 2,5-bis(6,9-bis(4-(tert-butyl)phenyl)-9H-carbazol-3-yl)pyrazine (TCz-3PA-TCz), 9-(5-(6,9-bis(4-(tert-butyl)phenyl)-9H-carbazol-3-yl)pyrazin-2-yl)-3,6-bis(4-(tert-butyl)phenyl)-9H-carbazole (TCz-3,9PA-TCz) and 2,5-bis(3,6-bis(4-(tert-butyl)phenyl)-9H-carbazol-9-yl)pyrazine (TCz-9PA-TCz), with a donor–acceptor–donor structure were synthesized and characterized. TCz-3,9PA-TCz in the thin solid powder state showed much higher thermal stability than TCz-3PA-TCz and TCz-9PA-TCz. The maximum photoluminescent emission wavelengths of TCz-3PA-TCz, TCz-3,9PA-TCz and TCz-9PA-TCz in toluene solution were 423, 435 and 454 nm, which were aggregation-induced quenching active. The absolute photoluminescent quantum yields of doped films for TCz-3PA-TCz, TCz-3,9PA-TCz and TCz-9PA-TCz were 10.75%, 4.46% and 16.70%, which were considerably improved relative to those of the pure film. The driving voltage, maximum external quantum efficiency, current efficiency, power efficiency and luminance of doped OLEDs based on TCz-9PA-TCz fabricated by spin coating were 4.0 V, 2.67%, 4.12 cd A−1, 2.46 lm w−1 and 8052 cd m−2. Furthermore, the doped OLEDs with TCz-3,9PA-TCz as a dopant fabricated by thermal deposition in vacuum showed a driving voltage of 3.5 V, maximum luminance of 6369.67 cd m2 and maximum external quantum efficiency of 3.85% at a brightness of 100 cd m−2. The linking model analogous to TCz-3,9PA-TCz was validated to be a more feasible way to combine pyrazine with carbazole moieties to produce highly efficient and stable electroluminescent blue light materials.