Organoboron Compounds with an 8-Hydroxyquinolato Chelate and Its Derivatives: Substituent Effects on Structures and Luminescence

Four new luminescent organoboron complexes have been synthesized and fully characterized. These compounds
are four-coordinate boron chelated by either 8-hydroxyquinolato (q) or functionalized 8-hydroxylquinolato ligands,
including BPh2(5-(1-naphthyl)-q) (1), BPh2(5-(2-benzothienyl)-q) (2), B(2-benzothienyl)2q (3), and B(2-benzothienyl)2(2-Me-q) (4). All four compounds have a tetrahedral geometry as established by X-ray diffraction analyses. In
solution, compounds 1−4 have an emission maximum at 534, 565, 501, and 496 nm, respectively, at room
temperature. They emit similar colors in the solid states without red shifts of the emission band due to the lack of
significant intermolecular interactions in the crystal lattices. The substituent group at C5 or C2 position of the
8-hydroxyquinolato ligand has been observed to have a significant impact on the emission energy and the emission
quantum efficiency of the boron complexes. Molecular orbital calculations (Gaussian 98) showed that the electronic
transition of 1 and 2 is a π−π* transition centered on the functionalized 8-hydroxyquinolato group and the electronic
transition of 3 and 4 is an interligand charge transfer from the 2-benzothienyl ligand to the hydroxyquinolato ring.
A double-layer electroluminescent device using 3 as the emitter has been fabricated, which produced a broad
emission band with a significant contribution of exciplex emission.

四例新型发光有机硼配合物已被合成并完成了全面的表征。这些化合物均为四配位硼，通过8-羟基喹啉酸根（q）或功能化的8-羟基喹啉酸根配体进行螯合，包括BPh2(5-(1-萘基)-q)（1）、BPh2(5-(2-苯并噻吩基)-q)（2）、B(2-苯并噻吩基)2q（3）和 B(2-苯并噻吩基)2(2-甲基-q)（4）。经X射线衍射分析确认，所有四种化合物均具有四面体几何结构。在室温下，化合物1−4在溶液中的发射光谱最大值分别为534、565、501和496纳米。在固态中，它们发出相似的颜色，且由于晶体晶格中分子间相互作用不显著，发射带未发生红移。观察到8-羟基喹啉酸根配体在C5或C2位置上的取代基对硼配合物的发射能和发射量子效率具有显著影响。分子轨道计算（Gaussian 98）表明，1和2的电子跃迁是以功能化8-羟基喹啉酸根为中心的π−π*跃迁，而3和4的电子跃迁则是从2-苯并噻吩基配体到羟基喹啉酸环的配体间电荷转移。以3为发射体的双层电致发光器件已被制备，该器件产生了一个具有明显激基复合物发射贡献的宽发射光谱。