Chelation-induced rigidification and turn-on fluorescence in β-diketone-incorporated hydrogen-bonded organic framework via host-guest interactions for selective Al³⁺ sensing.

We report a molecular engineering strategy that incorporates β-diketone recognition units into a hydrogen-bonded organic framework (HOF-101). The resulting β‑DK@HOF‑101 leverages hard‑soft acid‑base complementarity to achieve preferential Al³⁺ coordination, which in turn produces a pronounced turn‑on fluorescence response through the chelation‑enhanced fluorescence (CHEF) effect. This coordination-induced rigidification effectively suppresses non‑radiative decay and prolongs the excited‑state lifetime, an excitonic modulation rarely exploited in HOF‑based sensing systems. To address potential interference, a simple masking agent strategy is introduced to effectively suppress the quenching effects from transition metals such as Fe³⁺ and Cu²⁺. Moreover, by integrating a LeNet-5-based deep learning image recognition module, the platform enables automated fluorescence quantification, and its practical reliability is further validated through spike‑and‑recovery tests in lake water samples. Overall, this work establishes a design paradigm for water‑stable, turn‑on HOF‑based fluorescent sensors and provides a versatile blueprint for environmental and bioanalytical photonic devices.