Pyrenoimidazole-based deep-blue-emitting materials: optical, electrochemical, and electroluminescent characteristics

A series of pyrenoimidazoles that contained various functional chromophores, such as anthracene, pyrene, triphenylamine, carbazole, and fluorene, were synthesized and characterized by optical, electrochemical, and theoretical studies. The absorption spectra of the dyes are dominated by electronic transitions that arise from the pyrenoimidazole core and the additional chromophore. All of the dyes exhibited blue-light photoluminescence with moderate-to-high quantum efficiencies. They also displayed high thermal stability and their thermal-decomposition temperatures fell within the range 462-512 °C; the highest decomposition temperature was recorded for a carbazole-containing dye. The oxidation propensity of the dyes increased on the introduction of electron-rich chromophores, such as triphenylamine or carbazole. The application of selected dyes that featured additional chromophores such as pyrene, carbazole, and triphenylamine as blue-emissive dopants into multilayered organic light-emitting diodes with a 4,4'-bis(9H-carbazol-9-yl)biphenyl (CBP) host was investigated. Devices that were based on triphenylamine- and carbazole-containing dyes exhibited deep-blue emission (CIE 0.157, 0.054 and 0.163, 0.041), whereas a device that was based on a pyrene-containing dye showed a bright-blue emission (CIE 0.156, 0.135).