F−- and H+-triggered reversible supramolecular self-assembly/disassembly probed by a fluorescent Ru2+ complex

Abstract

A new strategy was proposed to monitor transition behavior involved in F⁻- and H⁺-triggered reversible supramolecular self-assembly/disassembly by using a Ru²⁺ complex (Ru(Phen)₃²⁺) as a fluorescent probe. N,N-Dibenzoyl-L-cystine (DBC) was used as gelator to form supramolecular gels. Fluorescent images of the fluorescent-labelled DBC gels indicate that Ru(Phen)₃²⁺ is dispersed in the gapping place of three-dimensional networks formed by fibrillar DBC aggregates. In a certain range of F⁻ concentrations, it was found that there is a good linear relationship (R² = 0.999) between F⁻ concentrations and the fluorescent intensity difference between the DBC gels and corresponding solutions. The phase transition temperature of DBC gels is increased with a decrease of F⁻ concentration. Interestingly, the addition of H⁺ to disassembled systems results in reassembly of DBC. The rate of H⁺-triggered reassembly is increased with an increase of the H⁺ concentration. SEM images of reassembled aggregates show no substantial difference in comparison with that of original DBC aggregates, indicating that the F⁻- and H⁺-triggered disassembly/reassembly is completely reversible. Time-dependent fluorescent spectra indicate that monitoring self-assembly/disassembly transitions by using the Ru²⁺ complex as a fluorescent probe is a fast and precise strategy.