Iron ions, one of the most common heavy metal pollutants in industrial waste materials, are continuously actively or passively delivered to the environment. Meanwhile, the importance of Fe³⁺ in biological processes in vivo can not be neglected due to its crucial role in maintaining normal physiological function. Therefore, a ratiometric fluorescence covalent organic framework (TD-COF) was constructed for tracking-by-detection of Fe³⁺. Alkynes-extended 1,3,6,8-tetrakis(4-ethynyl benzaldehyde)-pyrene (TEBPY) with complete planar structure and 2,5-dihydroxyterephthalohydrazide (DHTH) with functional group –OH were selected as the building blocks. The ratiometric fluorescence TD-COF with a dandelion-like structure exhibited its dual emission peaked at 510 nm and 630 nm. It displayed an obvious fluorescence color variation of yellow-red-black in the presence of Fe³⁺. Benefiting from the high luminescent efficiency (QY of 36.4%) and multiple identical binding sites, TD-COF exhibited a wide linear range to Fe³⁺ (0.005–50 μM) with a detection limit of 10.9 nM. Additionally, a smartphone visual sensing platform integrated with TD-COF was developed based on the color transformation and successfully applied to visual smart real-time monitoring Fe³⁺. More surprisingly, the maximum adsorption capacity of TD-COF towards Fe³⁺ was 833.3 mg/g due to the coordination interaction and cationic π-effect. The practicability of the smartphone-integrated ratiometric sensing platform for visual tracking-by-detection of Fe³⁺ was verified by choosing tap water as the actual sample, and the recoveries were calculated to be 98.71–100.88%. This work thus developed COF-based ratiometric sensing of Fe³⁺, which is an attractive candidate for further application in fluorescent sensing and visual monitoring.

铁离子是工业废料中最常见的重金属污染物之一，它不断地主动或被动地释放到环境中。同时，Fe ³⁺在体内生物过程中的重要性也不容忽视，因为它对维持正常的生理功能起着至关重要的作用。因此，构建了比率荧光共价有机框架（TD-COF）用于Fe ^{3+的跟踪检测。}. 选择具有完整平面结构的炔烃扩展的 1,3,6,8-四（4-乙炔基苯甲醛）-芘 (TEBPY) 和具有官能团 –OH 的 2,5-二羟基对苯二甲酰肼 (DHTH) 作为构建单元。具有类似蒲公英结构的比率荧光TD-COF在510 nm和630 nm处表现出双发射峰。^{在Fe 3+}存在下，它显示出明显的黄-红-黑色荧光颜色变化。得益于高发光效率（QY 为 36.4%）和多个相同的结合位点，TD-COF 对 Fe ^{3+表现出较宽的线性范围}(0.005–50 μM)，检测限为 10.9 nM。此外，基于颜色变换开发了集成TD-COF的智能手机视觉传感平台，并成功应用于视觉智能实时监测Fe ³⁺。更令人惊讶的是，由于配位相互作用和阳离子π效应，TD-COF对Fe ^{3+的最大吸附容量为833.3 mg/g。}以自来水为实际样品，验证了基于智能手机集成比例传感平台视觉跟踪检测Fe ^{3+的实用性，计算回收率为98.71~100.88%。因此，这项工作开发了基于 COF 的 Fe 3+}比例传感，这是进一步应用于荧光传感和视觉监测的有吸引力的候选者。