Reversible and Turn-On Fluorescence Detection of Phosphate in Aqueous Solution and Living Cell Imaging by Supramolecular Metallacycles with AIE-Active Ligands

Luminescent supramolecular metallacycles have attracted
great interest
as a new promising class of sensing substrates. In this work, two
tetraphenylethene (TPE)-based diimidazole and dipyrazole ligands with
the aggregation-induced emission (AIE) feature were designed for the
construction of supramolecular tetragonal metallacycles 1–4 with two 90° mononuclear [(bpy)M]2+ or dinuclear [(bpy)2M2]4+ acceptors (bpy = 2,2′-dipyridine; M = Pd, Pt), in which the
fluorescence can be quenched to an “off” state due to
the ligand-to-metal charge transfer (LMCT). Metallacycle 1 was utilized as a fluorescence sensor for phosphate (PO43–) detection in aqueous solution by means of disassembly,
leading to the release of the ligand. Additionally, the metallacycle
can be regenerated through self-assembly via the introduction of Pd(II)
acceptors. PO43– was detected using TPE-based
metallacycles over a wide concentration range, with a detection limit
as low as 2.1 × 10–8 M. Furthermore, sensor 1 also presented the semiquantitative visual detection ability
for PO43– in the test paper mode via
fluorescence changes. The aforementioned studies not only enhance
the current research on fluorescent materials but also offer a strategy
for the creation of stimuli-responsive supramolecular coordination
complexes.