(1-Naphthyl)phenylamino functionalized three-coordinate organoboron compounds: syntheses, structures, and applications in OLEDs

New three-coordinate organoboron compounds functionalized by a (1-naphthyl) phenylamino group, B(mes)(2)(dbp-NPB) (1), B(db-NPB)(3) (2), and B(dbp-NPB)(3) (3), have been synthesized. A variable temperature H-1 NMR study showed that the aryl groups around the boron center in these compounds have a rotation barrier similar to 70 kJ mol(-1). The new boron compounds are amorphous solids with T-g being 110 degrees C, 171 degrees C and 173 degrees C, respectively. The electronic properties of the new boron compounds were investigated by cyclic voltammetry and UV-visible spectroscopy. All three boron compounds are blue emitters in the solid state. In solution the emission spectra of the boron compounds shift toward a longer wavelength with increasing solvent polarity. In CH2Cl2, the emission quantum efficiency of the three compounds was determined to be 0.22, 0.27 and 0.23, respectively. Several series of electroluminescent (EL) devices where compounds 1-3 are used as either an emitter/electron transport material, a hole transport material, or a hole injection material have been fabricated and their performance has been compared to the corresponding devices of BNPB, a previously investigated molecule, NPB, a commonly used hole transport material, and CuPc, a commonly used hole injection material. The EL results indicate that the new boron compounds are not suitable as emitters/electron transport materials, but they are promising as hole transport and hole injection materials in EL devices.