Studies On Syntheses, Characterization, Luminescent Properties Of Organoboron Complexes With Imine Ligands

Luminescent coordination compounds have been one of the most active research areas because of their high quantum yields and stability in potential application of light emitting diodes (LEDs). The metal complexes with nitrogen-containing ligands have been synthesized and their luminescent behavior studied. The change of center metal ion, the size ofπ-conjugated system of the ligand and the electronic effect of substituents on the ligand are important factors for modulating its luminescent properties. The frequency and intensity of the luminescence of the complex are modulated via the design of the ligand-modified and center metal, so that luminescent properties are improved based on metal coordination compounds.Our research results indicate that the new chelating bidentate anilido-imine conjugated ligands are well suitable for synthesizing the four-coordinate organoboron complexes by a salt metathesis reaction of BF3(OEt2) with the lithium salt of corresponding ligands at–78 oC. 1H and 13C NMR spectra reveal that these boron complexes have Cs-symmetric structures in solution and X-ray diffraction analysis indicates that the six-membered chelating ring in these complexes is nearly planar with the boron atom lying slightly out of the plane. These new complexes 3a–3c produce bright fluorescence in both solution and the solid state, and show high quantum yields in solution. However complex 3d shows very poor luminescent property (low quantum yields) than the aluminum complex with the same ligand. It might be explained that boron atom without 3d unoccupied orbit can not accept the alone pair electron, thus influence its optical properties. In order to study the electron effect on these new organoboron complexes, we synthesized other three boron complexes. We found that the electon-poor substituents (Cl and F) of the conjugated aromatic ring make these complexes red shit (8~9 nm). Compared with Ortho-C6H4N(C6H3iPr2-2,6)(CH=NC6H3C6H4Me-p)BF2 (Ф= 0.57), complex 3a'(Ф= 0.50) has a lower quantum yield, due to the heavy atom effect of chlorine; Complex 3c'(Ф= 0.70) have a lower quantum yield than complex 3b'(Ф= 0.79), which is most likely due to the thermal motion of the conformationally mobile methoxy group, which results in energy loss via nonradiative decay.Two novel dinuclear boron complexes was designed and synthesized, and their luminescent properties have been studied. The two novel dinuclear boron complexes were characterized by 1H and 13CNMR spectroscopy, elemental analyses. These complexes show higher quantum yield than corresponding dinuclear dialkylaluminum complexes.