Benzothiaoline Three-Coordinated Organoboron Compounds with a BN Bond: Dual Emission and Temperature-Dependent Excimer Fluorescence

A series of 2,2-disubstituted benzothiazoline-BMes2 (Mes = mesityl) compounds containing a BN bond have been prepared and fully characterized. Their photophysical properties were investigated by UV–vis and fluorescence spectroscopy, which revealed the presence of solvent- and concentration-dependent dual emission. On the basis of the spectroscopic data, the dual emission was assigned to monomer and excimer fluorescence of the molecule, respectively. Experimental and TD-DFT computational data indicated that the purple-blue monomer emission of these compounds is mainly from an intramolecular charge transfer (CT) transition between the benzo-sulfur moiety and the boron center. The yellow-green excimer emission is attributed to intermolecular interactions involving the benzo-sulfur unit. Furthermore, the excimer emission maxima of all compounds were found to be sensitive to temperature, shifting to lower energy with decreasing temperature, which illustrates the potential for this class of compounds to be used as luminescent thermometers.一系列含硼氮双键的2,2-二取代苯并噻唑啉-BMes₂（Mes为均三甲苯基）类化合物已被制备并完成全面表征。采用紫外-可见（ultraviolet-visible, UV–vis）光谱与荧光光谱对其光物理性质进行系统研究，结果显示该类化合物存在溶剂与浓度依赖的双发射行为。基于上述光谱数据，该双发射分别被归属为该化合物的单体荧光与激基缔合物荧光。实验与含时密度泛函理论（time-dependent density functional theory, TD-DFT）计算数据表明，此类化合物的紫蓝色单体发射主要来源于苯并硫单元与硼中心之间的分子内电荷转移（intramolecular charge transfer, CT）跃迁。其黄绿色激基缔合物发射则归因于涉及该苯并硫单元的分子间相互作用。此外，所有此类化合物的激基缔合物发射峰位均对温度敏感，随温度降低向低能区发生红移，这表明该类化合物具备用作发光温度计的应用潜力。