Diphenylethenyl- and methylphenylethenyl-substituted triphenylamines as effective hole transporting and emitting materials

Diphenylethenyl- and methylphenylethenyl-substituted triphenylamines were prepared by condensation of trimethoxy-substituted triphenylamines with 2,2-diphenylacetaldehyde or 2-phenylpropionaldehyde respectively. The synthesized compounds were found to be capable of glass formation with glass transition temperatures above 49 °C for methylphenylethenyl-substituted derivatives and above 82 °C for diphenylethenyl-substituted compounds. The ionization potentials of the layers of the derivatives were found to be in the range of 5.31-5.44 eV. Time-of-flight hole drift mobility values of the glassy layer of tri(4-diphenylethenyl-2-methoxyphenyl)amine well exceeded 10−2 cm2/Vs at high electric fields at room temperature. The clear dependence of the charge mobilities on the positions of methoxy groups was observed. Compounds having methoxy groups at the meta positions of triphenylamine groups exhibited superior hole-transporting properties compared to the compounds having methoxy groups at the ortho positions. Blue-green emitting OLEDs based on triphenylamine derivatives exhibited relatively high efficiencies (brightness in order 10000 cd/m2 and current efficiency from 4 to 10 cd/A) as for the fluorescent OLEDs.