The Single-Crystal to Single-Crystal Transformation of Two Coordination Polymers Achieves Differential Fluorescence Detection of Levofloxacin

The single-crystal to single-crystal transformation provides a precise strategy for regulating the functional properties of coordination polymers. In this work, [CdL(CH 3 CH 2 OH)(H 2 O) 0.5 ] n ( Cd-1 ) with a 2D network structure was synthesized based on 2,2′-thiobis-4-pyridinecarboxylic acid ligand (H 2 L); then, [CdL] n ( Cd-2 ) with a 3D framework was accomplished through the single-crystal to single-crystal transformation under the stimulation of water molecules. Cd-1 and Cd-2 exhibited the ligand-centered emission peaks at 430, 466 nm and 416, 466 nm with the fluorescence lifetimes of 0.59 and 0.60 ns, respectively. Interestingly, Cd-1 showed fluorescence quenching in response to levofloxacin (LOFX) in ethanol solution, while Cd-2 exhibited a significant fluorescence enhancement effect in aqueous solution, in which these differentiated phenomena facilitated a contrastive identification of LOFX in practical applications. In addition, the detailed mechanism comparisons of their differential fluorescence response behaviors were further conducted. Notably, some portable detection devices based on Cd-2 had been developed for visual recognition of LOFX.