Blue-light-emitting multifunctional triphenylamine-centered starburst quinolines: synthesis, electrochemical and photophysical properties

A series of triphenylamine-centered starburst quinolines (1a-1g) have been synthesized by Friedl?nder condensation of the 4,4',4'-triacetyltriphenylamine (2) and 2-aminophenyl ketones (3a-3g) in the presence of catalytic sulfuric acid and characterized well. They are thermally robust with high glass transition temperatures (above 176.4 °C) and decomposition temperatures (above 406 °C). These compounds emit blue fluorescence with λ(max)(Em) ranging from 433 to 446 nm in dilute toluene solution and 461 to 502 nm in the solid-state and have a relatively high efficiency (Φ(u) = 0.98-0.57). 1a-1g have estimated ionization potentials (IP) of 4.54 to 6.45 eV which are significantly near or higher than those of well-known electron transport materials (ETMs), including tris(8-hydroxyquinoline)aluminium (Alq(3)) (IP = 5.7-5.9 eV), and previously reported oligoquinolines (IP = 5.53-5.81 eV). Quantum chemical calculations using DFT B3LYP/6-31G* showed the highest occupied molecular orbital (HOMO) of -5.05 to -4.81 eV, which is close to the work function of indium tin oxide (ITO). These results demonstrate the potential of 1a-1g as hole-transporting/light-emitting/electron-transport materials and the host-materials of a dopant for hole-injecting for applications in organic light-emitting devices.