An unconventional chromophore in water-soluble polysiloxanes synthesized via thiol-ene reaction for metal ion detection

The unconventional chromophore S -> Si coordination bonds is firstly found in water-soluble comb polysiloxanes (PETHs) with different ratios of polyether and mercaptopropyl groups as side chains. The PETHs are synthesized via efficient thiol-ene click reaction between polymercaptopropylmethylsiloxane (PMMS) and 2,5,8,11,14,17,20,23-octaoxahexacos-25-ene. The fluorescence is preliminarily assumed to be generated from through-space charge transfer because the S -> Si coordination bonds make it easier to occur. The existence of S Si coordination bonds is firstly proved by experiments, including synthesizing model compound and testing via quantum-chemical modeling (Digambara Patra, 2001), Si NMR, XPS spectra, and fluorescence spectra. Furthermore, the changing law of fluorescence intensity of those compounds with temperature, concentration and solvent are investigated. Fluorescence intensity improves with the temperature dropped down. This unconventional chromophore shows the AIEE (Valeur and Berberan-Santo, 2017) (aggregation-induced emission enhancement) phenomenon. The mercapto and thioether groups in PETHs can act on Hg2+ and Fe3+, breaking the Si S interaction and quenching the fluorescence. The quenching constant is determined by the Stern-Volmer equation. Therefore, the PETHs are used as fluorescence probes for Hg2+ and Fe3+ in water which may be applicable to metal detection. (C) 2017 Elsevier B.V. All rights reserved.