Department of Chemistry, Institute for Molecular Science and Fusion Technology, Kangwon National University, Chuncheon 24341, Korea.
Molecules. 2021 Mar 21;26(6):1763. doi: 10.3390/molecules26061763.
The photophysical properties of 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-9-carbazole-based --carboranyl compounds (, , , and ), in which an -carborane cage was appended at the C3-position of a 9-phenyl-9-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 and 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-9-carbazole moiety and weak intramolecular charge transfer (ICT) between the -carborane and the carbazole group. These compounds showed intense yellowish emission (λ = ~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 (S) of the compounds suggested that the strong emission bands can be assigned to the ICT transition involving the -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 < ‒H for < ‒CH for < ‒C(CH) for ). These features indicate that the ICT-based radiative decay process in rigid states is affected by the electronic environment of the 9-phenyl-9-carbazole group. Consequently, the efficient ICT-based radiative decay of -carboranyl compounds can be achieved by appending the -carborane cage with electron-rich aromatic systems.
基于卡硼烷的给体-受体二聚体的光物理性质已知受卡硼烷笼的电子环境影响，但供体部分的电子环境的影响尚不清楚。在此，合成了四个基于 9-苯基-9-咔唑的 --卡硼烷化合物（，，，和），其中 -卡硼烷笼附加在带有各种官能团的 9-苯基-9-咔唑部分的 C3 位置。通过多核核磁共振波谱和元素分析对其进行了充分的表征。此外，通过 X 射线衍射晶体学确定了和的固态分子结构。对于所有化合物，最低能量吸收带显示出延伸至 350nm 的尾部，归因于 9-苯基-9-咔唑部分的自旋允许的π-π*跃迁和 -卡硼烷和咔唑基团之间的弱分子内电荷转移（ICT）。这些化合物在刚性状态（在四氢呋喃（THF）中在 77 K 和在膜中）下显示出强烈的黄色发射（λ=~540nm），而在 298 K 的 THF 中观察到相当弱的发射。化合物的第一激发态（S）的理论计算表明，强发射带可以归因于涉及 -卡硼烷的 ICT 跃迁。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，在膜状态下的量子产率和辐射衰减常数随着 9-苯基上取代基的给电子能力的增加而逐渐增强（-F 对于 < -H 对于 < -CH 对于 < -C(CH) 对于 ）。这些特征表明，刚性状态下基于 ICT 的辐射衰减过程受 9-苯基-9-咔唑基团的电子环境影响。因此，通过将富电子芳族系统附加到 -卡硼烷笼上，可以实现基于 ICT 的有效辐射衰减。
