The photophysical properties of closo-ortho-carboranyl-based donor–acceptor dyads are known to be affected by the electronic environment of the carborane cage but the influence of the electronic environment of the donor moiety remains unclear. Herein, four 9-phenyl-9H-carbazole-based closo-ortho-carboranyl compounds (1F, 2P, 3M, and 4T), in which an o-carborane cage was appended at the C3-position of a 9-phenyl-9H-carbazole moiety bearing various functional groups, were synthesized and fully characterized using multinuclear nuclear magnetic resonance spectroscopy and elemental analysis. Furthermore, the solid-state molecular structures of 1F and 4T were determined by X-ray diffraction crystallography. For all the compounds, the lowest-energy absorption band exhibited a tail extending to 350 nm, attributable to the spin-allowed π–π* transition of the 9-phenyl-9H-carbazole moiety and weak intramolecular charge transfer (ICT) between the o-carborane and the carbazole group. These compounds showed intense yellowish emission (λ_em = ~540 nm) in rigid states (in tetrahydrofuran (THF) at 77 K and in films), whereas considerably weak emission was observed in THF at 298 K. Theoretical calculations on the first excited states (S₁) of the compounds suggested that the strong emission bands can be assigned to the ICT transition involving the o-carborane. Furthermore, photoluminescence experiments in THF‒water mixtures demonstrated that aggregation-induced emission was responsible for the emission in rigid states. Intriguingly, the quantum yields and radiative decay constants in the film state were gradually enhanced with the increasing electron-donating ability of the substituent on the 9-phenyl group (‒F for 1F < ‒H for 2P < ‒CH₃ for 3M < ‒C(CH₃)₃ for 4T). These features indicate that the ICT-based radiative decay process in rigid states is affected by the electronic environment of the 9-phenyl-9H-carbazole group. Consequently, the efficient ICT-based radiative decay of o-carboranyl compounds can be achieved by appending the o-carborane cage with electron-rich aromatic systems.

中文翻译：

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电子环境对9-苯基-9H-咔唑基邻碳硼烷基发光体辐射效率的影响

已知基于邻-邻-碳硼烷基的供体-受体二体的光物理性质受碳硼烷笼的电子环境的影响，但供体部分的电子环境的影响仍不清楚。此为4个9苯基-9- ħ -咔唑基闭合碳-邻-carboranyl化合物（1F，2P，3M，和4T），其中一个ö -carborane笼在一个9-苯基的C3-位置所附9小时合成了具有各种官能团的-咔唑部分，并使用多核核磁共振波谱法和元素分析对其进行了全面表征。此外，通过X射线衍射晶体学测定了1F和4T的固态分子结构。对于所有化合物，最低能量吸收谱带的尾巴延伸至350 nm，这归因于9-苯基-9 H-咔唑部分的自旋允许的π–π *跃迁和分子之间的弱分子内电荷转移（ICT）的Ó -carborane和咔唑基。这些化合物显示出强烈的淡黄色发射（_λem在刚性状态下（在77 K下在四氢呋喃（THF）中和在薄膜中）=〜540 nm），而在298 K下在THF中观察到相当弱的发射。关于化合物的第一激发态（S ₁）的理论计算表明：可以将强发射带分配给涉及邻碳烷的ICT过渡。此外，在THF‒水混合物中的光致发光实验表明，聚集诱导的发射是刚性状态下发射的原因。有趣的是，随着9-苯基上取代基的供电子能力的增强，薄膜态的量子产率和辐射衰减常数逐渐提高（对于1F <‒H对于2P <‒CH ₃对于1F <‒H，对于3M <C（CH ₃）₃为4T）。这些特征表明，在刚性状态下，基于ICT的辐射衰减过程受9-苯基-9 H-咔唑基团的电子环境影响。因此，高效的基于ICT的辐射衰减ö -carboranyl化合物可以通过附加来实现ø与富电子的芳族系统-carborane笼。