Synthesis of 2,6-diaryl-4,4-diphenyldithienosiloles and their luminescent properties

The dithienosilole (DTS) derivatives containing para-substituted phenyl with methyl, vinyl, or dimethylamino groups connected to the bithiophene moiety of the DTS was successfully synthesized by nickel-catalyzed Grignard coupling reactions. For the evaluation of the electroluminescent properties of these DTS derivatives, they were used as electron-transporting, emitting, or hole-transporting layers, respectively, in electroluminescent (EL) device fabrication processes. The device structures were ITO/TPD (40 nm)/Alq3 (50 nm)/DTS derivative (50 nm)/Al (type I), ITO/TPD (40 nm)/DTS derivative (50 nm)/Alq3 (20 nm)/Al (type II), and ITO/DTS derivative (50 nm)/Alq3 (50 nm)/Al (type III). Although its maximum current density was small, the 2,6-bis[4-(N,N-dimethylamino)phenyl]-4,4-diphenyldithienosilole (5) possessing a strong electron-donating group provided apparently lower turn-on voltage, although its maximum current density was small, in comparison with the one of previously reported TMS-DTS (2,6-bis(trimethylsilyl)-4,4-diphenyldithienosilole). The EL spectra of the DTS derivatives 3–5 exhibited maximum peaks at 512, 517, and 560 nm which correspond to green to yellowish-green light. The luminance of the devices containing the DTS derivatives 3–5 as an emitting layer shows 680, 515, and 250 cd/m2, respectively, at 10 V. From the evaluation of the utilities of the synthesized DTS derivatives 3–5, the derivative 3 among these materials can be used efficiently as an emitting material in the type II EL device.