Fluorescent Enhancement Of Guest Molecules By Supramolecular Hydrogel

Supramolecular gel is a kind of solid-like gel which has 3D matrix formed by self-assembly of gelator in solvent. This unique 3D matrix of supramolecular gel leads to the different fluorescent behaviors of the guest molecules in supramolecular gels from that in solution.In this paper, the fluorescent enhancement of rare earth ion Eu(Ⅲ) and Tb-PUFX in supramolecular hydrogels which formed by N, N-dibenzoyl-L-cystine (DBC) and 1,3:2,4-di-O-benzylidene-D-sorbitol (DBS) respectively were studied. The response of DBC hydrogel to F- and H⁺ probed by Ru(Phen)3 Cl2 was investigated. The results are as follows:1. It was found that the fluorescence of Eu(Ⅲ) in the DBC supramolecular gel increased significantly compared with that in solution. The varying temperature fluorescence spectra of DBC gels showed that fluorescent intensities of Eu(Ⅲ) in DBC gels decreased with an increase of temperature. The fluorescence decay spectra confirmed that fluorescence enhancement of Eu(Ⅲ) is related to the self-assembly of DBC. The phase transition temperature (TSG) of DBC gels increased with an increase of Eu(Ⅲ) concentration. The morphology of DBC aggregates in the presence of Eu(Ⅲ) shows highly entangled and thin fibrillar aggregates comparing with less entangled and thick aggregates in the absence of Eu(Ⅲ). The UV and FT-IR spectra of the DBC gels in the presence of Eu(Ⅲ) indicated the formation of complexation between Eu(Ⅲ) and oxygen atoms of DBC aggregates. The results reveal the mechanism of the luminescence enhancement of Eu(Ⅲ) in supramolecular hydrogels involves the interaction between Eu(Ⅲ) and DBC aggregates.2. DBS gel exhibits a sensitization effect on the fluorescence of Tb(Ⅲ)-PUFX. The fluorescent images showed that the Tb(Ⅲ)-PUFX was dispersed in the DBS gels. The varying temperature fluorescence spectra of Tb(Ⅲ)-PUFX in DBS gels indicated that the sensitization effect of DBS gel also exhibits thermo-reversibility. Fluorescence lifetime of Tb(Ⅲ)-PUFX in DBS gels is longer than that in corresponding solutions. The sensitization effect of DBS gel on the fluorescence of Tb(Ⅲ)-PUFX can be ascribed to a unique microstructure of three-dimensional network formed by DBC aggregates, resulting in deactivation of the nonradiative relaxation.3. The response of DBC hydrogel to F- and H⁺ probed by Ru(Phen)₃Cl₂ was investigated. The fluorescence intensities of Ru(Phen)₃Cl₂ in DBC gel decrease and increase with the concentration increase of F- and H⁺ respectively . The phase transition temperature (TSG) of DBC gels also changed with the concentration of F- and H⁺.The response of DBC hydrogel to F- and H⁺ attributed to F- can destroy the hydrogen bonds between DBC molecules and H⁺ can influence the dissociation of the H⁺ in carboxyl of DBC molecules, which leads to the dissociation of DBC aggregates.