Ratiometric Detection of Propyl Gallate Based on Two Zn(II)–Tb(III) Coordination Polymers Modulated by Metal–Ligand Ratios

Propyl gallate (PG) is used as an antioxidant in food. However, excessive use may pose potential health risks. Therefore, it is necessary to develop a method for accurate detection of PG. This study successfully synthesized two heterometallic Zn(II)–Tb(III) coordination polymers (CPs) controlled by metal-ligand ratios, {[Zn(tpy)2][Tb3(DCA)11]·H2O}n (1) and {[Zn(tpy)2][Tb4(DCA)14]}n (2) (DCA = 3,5-dichlorobenzoate; tpy = 2,2′:6′,2″-terpyridine). The two CPs both own the 0D + 1D ionic pair structure, but they display two distinct structures due to the different metal-ligand ratios. They exhibit intrinsic dual-emission and act as excellent ratiometric fluorescence sensors for the quantitative detection of PG, offering high selectivity, excellent anti-interference capability, rapid response, and good recyclability. The detection limits are as low as 0.38 and 0.35 μM for 1 and 2, respectively. Moreover, they can also detect PG in practical edible oil samples with good recovery rates. Interestingly, the smartphone-integrated RGB analysis platform based on the two sensors was established for portable detection of PG. Mechanistic studies indicate that the fluorescence quenching primarily results from the combined effects of competitive absorption and the dynamic quenching process. This work represents two rarely reported heterometallic CPs-based ratiometric sensors for PG detection, which have great potential for food safety.