Han Pauline J, Rheingold Arnold L, Trogler William C
Department of Chemistry and Biochemistry, University of California, San Diego , 9500 Gilman Drive, La Jolla, California 92093-0358, United States.
Inorg Chem. 2013 Oct 21;52(20):12033-45. doi: 10.1021/ic401850v. Epub 2013 Oct 4.
Luminescent homoleptic bismuth(III) complexes have been synthesized by adding several functionalized 8-hydroxyquinolate ligands to bismuth(III) chloride in a 3:1 mole ratio in either ethanol or tetrahydrofuran (THF) solvent. These complexes have been characterized by single-crystal X-ray diffraction (XRD) analysis, UV-vis spectroscopy, fluorescence spectroscopy, and density functional theory (DFT) calculations to determine their structures and photophysical properties. Reversible dimerization of the mononuclear tris(hydroxyquinolate) complexes was observed in solution and quantified using UV-vis spectroscopy. The fluorescence spectra show a blue shift for the monomer compared with homoleptic aluminum(III) hydroxyquinolate compounds. Four dimeric compounds and one monomeric isomer were characterized structurally. The bismuth(III) centers in the dimers are bridged by two oxygen atoms from the substituted hydroxyquinolate ligands. The more sterically hindered quinolate complex, tris(2-(diethoxymethyl)-8-quinolinato)bismuth, crystallizes as a monomer. The complexes all exhibit low-lying absorption and emission spectral features attributable to transitions between the HOMO (π orbital localized on the quinolate phenoxide ring) and LUMO (π* orbital localized on the quinolate pyridyl ring). Excitation and emission spectra show a concentration dependence in solution that suggests that a monomer-dimer equilibrium occurs. Electronic structure DFT calculations support trends seen in the experimental results with a HOMO-LUMO gap of 2.156 eV calculated for the monomer that is significantly larger than those for the dimers (1.772 and 1.915 eV). The close face to face approach of two quinolate rings in the dimer destabilizes the uppermost occupied quinolate π orbitals, which reduces the HOMO-LUMO gap and results in longer wavelength absorption and emission spectral features than in the monomer form.
通过在乙醇或四氢呋喃（THF）溶剂中，以3:1的摩尔比将几种功能化的8-羟基喹啉配体添加到氯化铋（III）中，合成了发光的纯配体铋（III）配合物。这些配合物已通过单晶X射线衍射（XRD）分析、紫外-可见光谱、荧光光谱和密度泛函理论（DFT）计算进行了表征，以确定它们的结构和光物理性质。在溶液中观察到单核三（羟基喹啉）配合物的可逆二聚化，并使用紫外-可见光谱进行了定量。与纯配体铝（III）羟基喹啉化合物相比，荧光光谱显示单体有蓝移。对四种二聚体化合物和一种单体异构体进行了结构表征。二聚体中的铋（III）中心由取代的羟基喹啉配体的两个氧原子桥连。空间位阻更大的喹啉配合物三（2-（二乙氧基甲基）-8-喹啉基）铋以单体形式结晶。这些配合物都表现出低能吸收和发射光谱特征，这归因于最高占据分子轨道（HOMO，位于喹啉酚盐环上的π轨道）和最低未占据分子轨道（LUMO，位于喹啉吡啶环上的π*轨道）之间的跃迁。激发光谱和发射光谱在溶液中显示出浓度依赖性，这表明存在单体-二聚体平衡。电子结构DFT计算支持了实验结果中观察到的趋势，计算出单体的HOMO-LUMO能隙为2.156 eV，明显大于二聚体的能隙（1.772和1.915 eV）。二聚体中两个喹啉环的面对面紧密排列使最上层占据的喹啉π轨道不稳定，这降低了HOMO-LUMO能隙，并导致比单体形式更长波长的吸收和发射光谱特征。
