State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012, P. R. China.
Department of Chemistry, Biochemistry, & Physics, Florida Southern College, 111 Lake Hollingsworth Dr, Lakeland, Florida 33801, United States.
J Am Chem Soc. 2022 Sep 21;144(37):17054-17063. doi: 10.1021/jacs.2c06680. Epub 2022 Sep 7.
Distinct from predominately known fluorescence quenching (turn-off) detection, turn-on response to hazardous substances by luminescent metal-organic frameworks (LMOFs) could greatly avoid signal loss and susceptibility to environmental stimulus. However, such detection rarely occurs and lacks theoretical elucidations. Here, we present the first example of unique turn-on and unprecedented turn-off-on responses to a variety of acids by a stable 12-connected hexanuclear Y(III)-cluster-based LMOF material─, featuring the nondefault topology. Benefiting from the "pocket" structures formed by the carbazole-containing ligands, can sense multiple inorganic and organic acids via different degrees of fluorescence turn-on behaviors. Particularly, turn-on sensing of HNO, HCl, HBr, and TFA is hypersensitive with LODs as low as the ppb level. Theoretical calculations confirm weak interactions in acid-ligand complexes, which lead to constrained rotations of benzene moieties of the ligands when the complexes decay from excited states. These account for the turn-on response through reduced nonradiative energy consumption that competes with emissive decay. The turn-off-on response to 4-NBA and 3,5-DNBA involves an excited-state electron transfer process that dominates the turn-off stage and prohibited nonradiative decay that competes with the intrinsic emission of the ligand and dominates the turn-on stage. This work has a guiding significance for the full-scale understanding of turn-on and turn-off-on sensing performance in LMOF materials and beyond.
与主要的荧光猝灭（关闭）检测不同，发光金属-有机骨架（LMOFs）对有害物质的开启响应可以大大避免信号损失和对环境刺激的敏感性。然而，这种检测很少发生，也缺乏理论解释。在这里，我们首次展示了一种稳定的 12 连接的六核钇（III）簇基 LMOF 材料─对各种酸具有独特的开启和前所未有的关闭-开启响应的示例，其具有非默认拓扑结构。受益于含有咔唑的配体形成的“口袋”结构， 可以通过不同程度的荧光开启行为来感应多种无机和有机酸。特别是，对 HNO、HCl、HBr 和 TFA 的开启感应具有超灵敏性，LOD 低至 ppb 级。理论计算证实了酸-配体复合物中的弱相互作用，当复合物从激发态衰减时，这些相互作用导致配体中苯环部分的受限旋转。这解释了通过减少与发射衰变竞争的非辐射能量消耗来实现开启响应。对 4-NBA 和 3,5-DNBA 的关闭-开启响应涉及到一个激发态电子转移过程，该过程主导了关闭阶段，并禁止与配体的本征发射竞争并主导开启阶段的非辐射衰变。这项工作对于全面理解 LMOF 材料及其他材料中的开启和关闭-开启感应性能具有指导意义。
