Fluorophore branching boosted photo-induced energy transfer in UiO-66 for ultrasensitive and instant hydrazine sensing

Abstract

Metal organic frameworks (MOFs) have made great progress in the field of fluorescent sensing; however, whether the electronic structure and recognized sites can be adjusted by external functionalization still remains challenging. Here, by postmodifying 5-carboxyfluorescein (Flu), externally coupled orbitals were introduced into the electronic structure of UiO-66-OH, and thus an effective photo-induced energy transfer (PET) process was established in functionalized MOFs (UiO-66-Flu), resulting in the reduction of the intrinsic blue fluorescence. Due to the formation of the ester bond by effective incorporation of the surface –OH with Flu, the hydrazinolysis reaction triggered by hydrazine could happen and the Zr₆O₆ clusters could further reduce the reaction energy barrier through strong hydrogen bonding with hydrazine, resulting in a remarkably low limit of detection (LOD, 27.17 nM) and a fast response (4 s). Furthermore, with polyvinylidene fluoride (PVDF) as the dispersion medium, UiO-66-Flu was fabricated into a UiO-66-Flu/PVDF film sensor, enabling the rapid detection of gaseous hydrazine within 2 s in simulated practical scenarios. We expect that the present fluorescent ligand modifying concept will not only deepen the understanding of electronic structure engineering in functionalized MOF design, but also shine light on the exploration of high-performance MOF-based sensing strategies.