Effects of boron doping on the structural and optoelectronic properties of 9,10-diarylanthracenes
作者:Claas Hoffend、Martin Diefenbach、Estera Januszewski、Michael Bolte、Hans-Wolfram Lerner、Max C. Holthausen、Matthias Wagner
DOI:10.1039/c3dt51035b
日期:——
Key structural and optoelectronic properties of 9,10-dihydro-9,10-diboraanthracene (DBA) derivatives carrying mesityl (2a), 2-methylnaphthyl- (2b) and 9-phenyl-2,7-di-tert-butylanthryl (2c) substituents at the boron atoms have systematically been compared with the properties of their all-carbon congeners 4a–c. The experimental investigations have been augmented by quantum-chemical calculations. Steric repulsion leads to large dihedral angles between the aryl substituents and the DBA (2a–c) or anthrylene (4a–c) cores; as a result, the B–C bonds of 2a–c are kinetically shielded from hydrolysis and oxidative degradation. Lithium metal reduces the mesityl derivative 2a to the inverse sandwich complexes [Li(OR2)n]2[2a] (X-ray crystallography; OR2 = THF, n = 2; Et2O, n = 1). In line with the nodal structures of the LUMO of 2a/HOMO of [Li(THF)2]2[2a], the C–C bond lengths of the anionic fragment [2a]2− show characteristic differences to those of 2a and come close to the C–C bond lengths of the isoelectronic species 4a. X-ray crystallography on anti-2b × 2 C6H6 and anti-4b × 2 C6H6 reveals an essentially identical packing of the main molecules. The benzene solvate molecules, however, interact in a very different manner with anti-2b or anti-4b, which can be traced down to subtle disparities between the electron density distributions of the two compounds. 2a–c undergo a photoinduced aryl-to-DBA charge transfer; the back electron transfer results in blue (2a), green (2b) and red (2c) emission, albeit with low quantum yields. 4a–c are characterised by a local π–π* photoexcitation of the central 9,10-anthrylene fragments and corresponding blue emission. Each of the compounds 2a–c gives rise to two reversible DBA-centred one-electron transitions in the cyclic voltammogram.
我们系统地比较了在硼原子上带有介子基(2a)、2-甲基萘基(2b)和 9-苯基-2,7-二叔丁基蒽基(2c)取代基的 9,10-二氢-9,10-二硼杂蒽 (DBA) 衍生物的主要结构和光电特性,以及它们的全碳同系物 4a-c 的特性。量子化学计算对实验研究进行了补充。立体斥力导致芳基取代基与 DBA(2a-c)或蒽(4a-c)核心之间形成较大的二面角;因此,2a-c 的 B-C 键在动力学上免受水解和氧化降解的影响。金属锂将甲苯二酚衍生物 2a 还原成反夹心复合物 [Li(OR2)n]2[2a] (X 射线晶体学;OR2 = THF,n = 2;Et2O,n = 1)。与 2a 的 LUMO/[Li(THF)2]2[2a]的 HOMO 的节点结构一致,阴离子片段 [2a]2- 的 C-C 键长度与 2a 的 C-C 键长度显示出特征性差异,并接近等电子物种 4a 的 C-C 键长度。反 2b × 2 C6H6 和反 4b × 2 C6H6 的 X 射线晶体学显示,主分子的堆积基本相同。然而,苯溶胶分子与反-2b 或反-4b 的相互作用方式却截然不同,这可以追溯到两种化合物电子密度分布之间的微妙差异。2a-c 发生光诱导的芳基-DBA 电荷转移;反向电子转移导致蓝色(2a)、绿色(2b)和红色(2c)发射,尽管量子产率较低。4a-c 的特点是中央 9,10-蒽片段发生局部 π-π* 光激发,并发出相应的蓝色发射。在循环伏安图中,2a-c 每种化合物都会产生两个以 DBA 为中心的可逆单电子跃迁。