Rubin Heather N, Reynolds Melissa M
Department of Chemistry , Colorado State University , Fort Collins , Colorado 80523 , United States.
School of Biomedical Engineering , Colorado State University , Fort Collins , Colorado 80523 , United States.
Inorg Chem. 2019 Aug 19;58(16):10671-10679. doi: 10.1021/acs.inorgchem.9b00481. Epub 2019 Jul 22.
Metal-organic frameworks (MOFs) are powerful chemosensors when designed to undergo a detectable change in optical properties upon interacting with target analytes. This work contributes to the overall understanding of metal-ion interactions with MOFs to elicit changes in fluorescence emission, a necessary step en route to developing more sensitive and selective systems for metal-ion sensing. Toward this goal, the photophysical properties of an amino-containing MOF, Cu(NHBTC), were investigated. The MOF was highly sensitive for the detection of Fe and Fe exhibiting the most intense fluorescence quenching with the lowest detectable change in signal occurring at 1.55 ppm (27.8 μM) at room temperature in minutes. Other metal ions, including Pb, Cu, Mn, Ni, and Co, were also detected at 5.7, 12, 3.0, 1.6, and 0.2 ppm, respectively, demonstrating the range of sensing capabilities. Additional experiments were performed to elucidate the pathway of metal-ion detection, including the investigation of photoluminescent changes upon the introduction of acids (HCl, ZrCl, and AlCl) and several anions (CO, OAc, and CrO). To determine the influence of the amino functional group on interactions with the analytes, isoreticular CuBTC and postsynthetically modified Cu(NHBTC) (to hinder access to the free-amine moiety) were also investigated, revealing that the free amine is essential for the detection of the anions and is likely involved in the detection of several divalent metal ions. On the other hand, divalent metal ion Fe likely induces an emission intensity change by interaction with the carboxylate of the MOF ligand or the open Cu sites. Taken together, this report demonstrates that Cu(NHBTC) has unique photoluminescent properties and likely elicits detection of ions (ppm, μM) via multiple pathways. As such, future development of MOF-based sensors should include MOFs with free accessible functional handles (such as an amine) to be strategically modified to selectively detect specific metal ions.
金属有机框架材料（MOFs）在设计为与目标分析物相互作用时发生可检测的光学性质变化时，是强大的化学传感器。这项工作有助于全面理解金属离子与MOFs的相互作用，以引发荧光发射的变化，这是开发更灵敏和选择性的金属离子传感系统的必要步骤。为了实现这一目标，研究了一种含氨基的MOF，Cu(NHBTC)的光物理性质。该MOF对Fe和Fe的检测高度敏感，在室温下几分钟内，在1.55 ppm（27.8 μM）时表现出最强烈的荧光猝灭，信号变化的最低可检测值。其他金属离子，包括Pb、Cu、Mn、Ni和Co，也分别在5.7、12、3.0、1.6和0.2 ppm时被检测到，展示了传感能力的范围。进行了额外的实验以阐明金属离子检测的途径，包括引入酸（HCl、ZrCl和AlCl）和几种阴离子（CO、OAc和CrO）后光致发光变化的研究。为了确定氨基官能团对与分析物相互作用的影响，还研究了等规CuBTC和后合成修饰的Cu(NHBTC)（以阻碍对游离胺部分的 access），结果表明游离胺对于阴离子的检测至关重要，并且可能参与了几种二价金属离子的检测。另一方面，二价金属离子Fe可能通过与MOF配体的羧酸盐或开放的Cu位点相互作用而引起发射强度变化。综上所述，本报告表明Cu(NHBTC)具有独特的光致发光性质，并且可能通过多种途径引发离子（ppm，μM）的检测。因此，基于MOF的传感器的未来发展应包括具有可自由访问的功能手柄（如胺）的MOF，以便进行策略性修饰以选择性检测特定金属离子。
