Stepwise Conformational Restriction of Acylhydrazone‐Based Molecules for High Signal‐to‐Noise Fluorescent Recognition of Synthetic Cannabinoid FUB‐INACA

Establishing explicit correlations among material dimensionality, luminescent properties, and sensing performance is of critical importance for the rational design of sensing materials with superior detection performance. Herein, employing 1H-imidazole-4, 5-dicarbohydrazide (IDA) and triphenylamine (TPA) derivatives as the fundamental building blocks, we propose a stepwise conformational restriction strategy to construct acylhydrazone-based discrete molecules (0D), linear polymers (1D), and covalent organic framework (COF, 2D) with progressively reduced conformational freedom. Upon interaction with FUB-INACA through synergistic multiple non-covalent interactions and hydrophobic effects, photoinduced electron transfer (PET) or intramolecular charge transfer (ICT) processes are activated, resulting in pronounced fluorescence modulation and enabling selective recognition. The higher-dimensional TFPA-IDA COF, featuring the most restricted conformational environment and the lowest baseline emission, delivers rapid (