Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore-560012 (India), Fax: (+91) 80-2360-1552.
Chemistry. 2014 Feb 17;20(8):2276-91. doi: 10.1002/chem.201302455. Epub 2014 Jan 23.
Three new electron-rich metal-organic frameworks (MOF-1-MOF-3) have been synthesized by employing ligands bearing aromatic tags. The key role of the chosen aromatic tags is to enhance the π-electron density of the luminescent MOFs. Single-crystal X-ray structures have revealed that these MOFs form three-dimensional porous networks with the aromatic tags projecting inwardly into the pores. These highly luminescent electron-rich MOFs have been successfully utilized for the detection of explosive nitroaromatic compounds (NACs) on the basis of fluorescence quenching. Although all of the prepared MOFs can serve as sensors for NACs, MOF-1 and MOF-2 exhibit superior sensitivity towards 4-nitrotoluene (4-NT) and 2,4-dinitrotoluene (DNT) compared to 2,4,6-trinitrotoluene (TNT) and 1,3,5-trinitrobenzene (TNB). MOF-3, on the other hand, shows an order of sensitivity in accordance with the electron deficiencies of the substrates. To understand such anomalous behavior, we have thoroughly analyzed both the steady-state and time-resolved fluorescence quenching associated with these interactions. Determination of static Stern-Volmer constants (KS) as well as collisional constants (KC) has revealed that MOF-1 and MOF-2 have higher KS values with 4-NT than with TNT, whereas for MOF-3 the reverse order is observed. This apparently anomalous phenomenon was well corroborated by theoretical calculations. Moreover, recyclability and sensitivity studies have revealed that these MOFs can be reused several times and that their sensitivities towards TNT solution are at the parts per billion (ppb) level.
三种新型富电子金属有机骨架（MOF-1-MOF-3）已通过使用带有芳香族标记的配体合成。所选芳香族标记的关键作用是增强发光 MOF 的π电子密度。单晶 X 射线结构表明，这些 MOF 形成具有三维多孔网络，芳香族标记向内突出到孔中。这些高发光富电子 MOF 已成功用于基于荧光猝灭的爆炸硝基芳香族化合物（NAC）的检测。虽然所有制备的 MOF 都可以作为 NAC 的传感器，但 MOF-1 和 MOF-2 对 4-硝基甲苯（4-NT）和 2,4-二硝基甲苯（DNT）的灵敏度高于 2,4,6-三硝基甲苯（TNT）和 1,3,5-三硝基苯（TNB）。另一方面，MOF-3 对底物的电子不足显示出敏感性顺序。为了理解这种异常行为，我们彻底分析了与这些相互作用相关的稳态和时间分辨荧光猝灭。静态 Stern-Volmer 常数（KS）和碰撞常数（KC）的测定表明，MOF-1 和 MOF-2 与 4-NT 的 KS 值高于 TNT，而 MOF-3 则相反。这种明显异常的现象得到了理论计算的很好证实。此外，可回收性和灵敏度研究表明，这些 MOF 可以重复使用多次，并且它们对 TNT 溶液的灵敏度达到十亿分之几（ppb）的水平。
