New divinylene trimers with triphenylpyridine segments: Synthesis, photophysics, electrochemical and electroluminescent properties

Three new trimers PV, FV and CV were synthesized by Heck coupling of 4(4-bromophenyl)-2,6-diphenylpyridine with substituted divinylbenzene, divinylfluorene and divinylcarbazole, respectively. They were very soluble in chloroform, dichloromethane, tetrahydrofuran and toluene. FV and CV were more thermally stable and showed higher glass transition temperature than PV. Their absorption maximum was located at 327–397 nm with optical band gap of 2.53–2.73 eV. FV and CV emitted blue-green light with emission maximum at 455–489 nm while PV emitted green-yellow light with emission maximum at 496–530 nm. Upon protonation, the trimer thin films displayed red-shifts of the emission maximum. The electrochemical and electroluminescent properties of the trimers were studied. Light-emitting diodes (LEDs) based on these trimers were fabricated. These LEDs showed bright blue light for FV, CV and bluish-green light for PV which are in line with their photoluminescence spectra. The maximum brightness was reached approximate 1000 cd/m2 for PV, 380 for FV, and 400 for CV, at current density of 200 mA/cm2.