Laser & Plasma Technology Division, Bhabha Atomic Research Centre, Mumbai-400 085, India.
J Phys Chem B. 2012 May 10;116(18):5551-8. doi: 10.1021/jp301266q. Epub 2012 Apr 30.
Molecules of the coumarin family have fluorescence characteristics that are highly sensitive to their environment, and thus, they have been used as fluorescent sensors in chemical and biological systems. However, the very poor fluorescence yield of most coumarin dyes in aqueous media limits their applications. We have adopted a supramolecular strategy to improve the fluorescence intensity of coumarin dye through its interaction with the relatively new host cucurbit[7]uril (CB[7]). The virtually nonfluorescent coumarin 1 (Φ(f) = 0.04) was converted into a highly fluorescent (Φ(f) = 0.52) entity in water upon addition of the nonfluorescent host CB[7]. Various spectroscopy techniques, namely, UV-vis absorption and steady-state and time-resolved fluorescence spectroscopies, established the formation of a strong 1:1 dye-CB[7] inclusion complex with a high binding constant of (1.2 ± 0.1) × 10(5) M(-1) for the dye. The stable inclusion complex of the neutral molecule was supported by density-functional-theory- (DFT-) based quantum chemical calculations. Energy decomposition analysis of various interaction factors in the host-guest complex revealed that key components providing stability to the complex were electrostatic, polarization, and charge-transfer energies. These new results on the formation of a strong inclusion complex of the versatile fluorophore coumarin 1 with the nontoxic host CB[7] could lead to the design of efficient molecular-scale biological probes, sensors, and photostable aqueous UV dye lasers.
香豆素家族的分子具有对其环境高度敏感的荧光特性，因此，它们已被用作化学和生物系统中的荧光传感器。然而，大多数香豆素染料在水介质中的荧光产率非常低，限制了它们的应用。我们采用超分子策略通过与相对较新的主体葫芦[7]脲（CB[7]）相互作用来提高香豆素染料的荧光强度。几乎没有荧光的香豆素 1（Φ(f) = 0.04）在加入非荧光主体 CB[7]后在水中转化为高荧光（Φ(f) = 0.52）实体。各种光谱技术，即紫外-可见吸收和稳态和时间分辨荧光光谱，确定了形成强 1:1 染料-CB[7]包合物，其结合常数为（1.2 ± 0.1）×10(5) M(-1)。中性分子的稳定包合物得到基于密度泛函理论（DFT）的量子化学计算的支持。在主体-客体配合物中各种相互作用因素的能量分解分析表明，为配合物提供稳定性的关键组件是静电、极化和电荷转移能。关于多功能荧光团香豆素 1与无毒主体 CB[7]形成强包合物的这些新结果可能导致设计高效的分子尺度生物探针、传感器和光稳定的水基紫外染料激光器。
