Three new 2,7-fluorenevinylene-based trimers were synthesized and characterized. The synthesis was carried out by the Heck coupling reaction of 9,9-dihexyl-2,7-divinylfluorene with 2-(4-bromophenyl)-5-phenyl-1,3,4- oxadiazole, N,N-diphenyl-4-bromoaniline, or 3-bromopyrene to afford the trimers OXD, TPA, and PYR, respectively. All the trimers were readily soluble in common organic solvents such as tetrahydrofuran, dichloromethane, chloroform, and toluene. Their glass transition temperatures ranged from 33 to 60°C. The UV-vis spectra showed an absorption maximum at λa,max = 379-417 nm with optical band gap of Eg = 2.47-2.66 eV. In solution, they emitted strong blue-green photoluminescence (PL) with PL maximum at λf,max = 455-565 nm and fluorescence quantum yield of Φf = 0.65-0.74. On the other hand, in their spin-coated films, the PL efficiencies significantly decreased due to the presence of concentration quenching. All samples showed nanosecond transient lifetime containing two components, suggesting excimer formation. The organic light-emitting diodes (OLEDs) with OXD and TPA showed green emission with electroluminescence (EL) quantum efficiencies of ηEL ∼ 10-2%, while very weak EL efficiency of ηEL ∼ 10-5% was observed with PYR. The highest occupied molecular orbital (HOMO) levels of the films were found to be 5.05-5.75 eV.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry