Department of Chemistry, Indian Institute of Technology, Kanpur 208016, India.
School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram (IISER TVM), Vithura 695551, Kerala, India.
Inorg Chem. 2020 May 4;59(9):6202-6213. doi: 10.1021/acs.inorgchem.0c00307. Epub 2020 Apr 15.
A zinc metal-organic framework, i.e., Zn-MOF (Zn-DBC), with ca. 27% solvent-accessible void volume was synthesized from a rationally designed tetraacid based on sterically insulated dibenzo[,]chrysene core; the latter inherently features concave shapes. Due to rigidification of the fluorophore in the MOF, Zn-DBC exhibits a respectable fluorescence quantum yield of ca. 30% in the solid state. The fluorescent and water-stable Zn-DBC MOF was found to display intriguing temperature-dependent emission behavior with an activation barrier of 1.06 kcal/mol for radiationless deactivation from the singlet-excited state. It is shown that the Zn-MOF can be employed as an efficient sensory material for detection of hazardous "quat" dicationic herbicides in water by diffusion-limited "turn-off" fluorescence. Due to confinement of the cationic guest analytes within the pores of the MOF, the fluorescence quenching via excited-state charge transfer mechanism is shown to depend on the molecular size of the analyte in addition to the redox potentials. Remarkably, Zn-DBC permits sensing of DQ, a well-known toxic "quat" herbicide, with a detection limit as low as 2.8 ppm in water. The unique structural attributes of the Zn-MOF for highly efficient fluorescence sensing of toxic herbicides in water are thus exemplified for the first time.
一种锌金属有机骨架，即 Zn-MOF（Zn-DBC），具有约 27%的溶剂可及空隙体积，是由一种基于空间隔离二苯并[,]苝核的四酸合理设计合成的；后者固有地具有凹形。由于在 MOF 中荧光团的刚性化，Zn-DBC 在固态下表现出约 30%的相当可观的荧光量子产率。发现荧光和水稳定的 Zn-DBC MOF 表现出有趣的温度依赖发射行为，其从单重激发态无辐射去活的活化能垒为 1.06 kcal/mol。结果表明，Zn-MOF 可以用作一种有效的传感材料，通过扩散限制的“关闭”荧光检测水中危险的“季铵”二价阳离子除草剂。由于阳离子客体分析物被限制在 MOF 的孔内，通过激发态电荷转移机制的荧光猝灭被证明不仅依赖于分析物的分子大小，还依赖于氧化还原电位。值得注意的是，Zn-DBC 允许以低至 2.8 ppm 的检测限检测 DQ，一种众所周知的有毒“季铵”除草剂。因此，Zn-MOF 的独特结构属性首次被证明可用于水中有毒除草剂的高效荧光传感。
