Highly specific fluorescent probes toward acetic acid via structural transformation of zinc complexes

Abstract

A highly sensitive and specific acetic acid probe is desirable to distinguish acetic acid from other fatty acids. Herein, we designed and synthesized two zinc complexes, H₂tBuCarPyZn₂Br₄(AcO)₂·AcOH (1) and H₂tBuCarPyZn₂Br₄(AcO)₂ (2). Both complexes exhibit fluorescence with emission peaks at 500 nm for complex 1 and 550 nm for complex 2, respectively. The DFT calculation shows that the transition from Br to the H₂tBuCarPy ligand is mainly responsible for the yellow emission of complex 2, while for complex 1 the valence band consists of Br and acetic acid solvent, and the participation of acetic acid in complex 1 could result in the blue-shift of emission compared with that of complex 2. Interestingly, an obvious blue-shift of emission was observed when complex 2 was exposed to an acetic acid atmosphere. Besides, the as-exposed complex 2 could recover to the initial state once the acetic acid atmosphere was removed. PXRD results demonstrate that the phase change from complex 2 to complex 1 after absorbing the acetic acid vapor accounts for the vapor-chromism. Then complex 2 was developed as an acetic acid probe, exhibiting high sensitivity and selectivity and excellent fatigue resistance.