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

Abstract

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 1 H NMR study showed that the aryl groups around the boron center in these compounds have a rotation barrier y70 kJ mol 21 . The new boron compounds are amorphous solids with T g being 110 uC, 171 uC and 173 uC, 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 CH 2 Cl 2 , 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. ExperimentalAll starting materials were purchased from Aldrich Chemical Company and used without further purification. Solvents were freshly distilled over appropriate drying reagents. All experiments were carried out under a dry nitrogen atmosphere using

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“…The 19.2(1) kcal mol À1 activation energy of the third process, BÀCM es group rotation,o f 1S-Me is much higherthan the rotationbarrierobserved previously in triarylboranes peciess uch as BMes 2 Ar (Ar = phenylo r duryl). [8] These processes of major-minor Mes rotationa nd their back-and-forth motions aroundt he boron atom, asi llustrated in Figure 3, are believed to be collectively responsible for the overall diastereomer exchange phenomenon in these systems.…”