Yang Shuai-Liang, Liu Wan-Shan, Li Gen, Bu Ran, Li Peng, Gao En-Qing
Shanghai Key Laboratory of Green Chemistry and Chemical Processes, School of Chemistry and Molecular Engineering, East China Normal University, Shanghai 200062, China.
College of Chemistry and Materials Science, Huaibei Normal University, Anhui 235000, China.
Inorg Chem. 2020 Oct 19;59(20):15421-15429. doi: 10.1021/acs.inorgchem.0c02419. Epub 2020 Oct 6.
Due to its great relevance to environmental, biological, and chemical processes, the precise detection of pH or acidic/basic species is an ongoing and imperative need. In this context, pH-sensitive luminescent systems are highly desired. We reported a three-dimensional Zn(II) MOF synthesized from a bipyridyl-tetracarboxylic ligand and composed of 4-fold interpenetrated diamond frameworks. Because the steric hindrance in the ligand prevents metal coordination with the pyridyl group, the MOF features free basic N sites accessible to the small H ions, which renders pH responsivity. The aqueous dispersion exhibits an abrupt, high-contrast, and reversible on-off fluorescence transition in the narrow pH range of 5.4-6.2. The sensitive bistable system can be used for the precise monitoring of pH within the range and for use as a pH-triggered optical switch. The responsive mechanism through pyridyl protonation is collaboratively supported by data fitting, absorption spectra, and molecular orbital calculations. In particular, spectral and theoretical analyses reveal the destruction of n → π* transitions and the appearance of intramolecular charge-transfer transitions upon pyridyl protonation. Moreover, by virtue of the pH-responsive fluorescence, the MOF shows appealing sensing performance for the detection of 3-nitropropionic acid, a major mycotoxin in moldy sugar cane.
由于其与环境、生物和化学过程高度相关，精确检测pH值或酸性/碱性物质是一项持续且迫切的需求。在此背景下，对pH敏感的发光系统备受期待。我们报道了一种由联吡啶四羧酸配体合成的三维Zn(II)金属有机框架（MOF），它由四重穿插的金刚石框架组成。由于配体中的空间位阻阻止了金属与吡啶基配位，该MOF具有可供小H离子接触的游离碱性N位点，这使其具有pH响应性。水分散体在5.4 - 6.2的窄pH范围内呈现出突然的、高对比度且可逆的开关荧光转变。这种灵敏的双稳态系统可用于该范围内pH值的精确监测，并用作pH触发的光学开关。通过吡啶基质子化的响应机制得到了数据拟合、吸收光谱和分子轨道计算的共同支持。特别地，光谱和理论分析揭示了吡啶基质子化时n → π*跃迁的破坏以及分子内电荷转移跃迁的出现。此外，凭借pH响应荧光，该MOF对发霉甘蔗中的主要霉菌毒素3 - 硝基丙酸的检测表现出诱人的传感性能。
