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) 2 M 2 ] 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 (PO 4 3- ) 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. PO 4 3- 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 PO 4 3- 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.