Study On The Enhancement Of Fluorescence Emission Induced By Supramolecular Gel

Nowadays, supramolecular gels formed by low molecular mass gelators have been received many attentions because of special structures of gelators. Supramolecular gel is a kind of solid-like gel which has 3D matrix formed by self-assembled of gelator in solvent. This unique 3D matrix of supramolecular makes the behaviors of the guest molecules different in supramolecular gels and in solution.In this paper, the property of the supramolecular organogels which formed by benzylidene-D-sorbitol derivatives 1,3:2,4-di-O-benzylidene-D-sorbitol (DBS) and the supramolecular hydrogels which formed by 3-{[(2R)-2-(Octadecylamino)-3-phenyl propanoyl]Amino}butyrate (TC18PheBu) were studied. The fluorescence behaviors of Rhodamin 6G(R6G),Acridine Orange(AO) and Criprofloxacin(CPFX) in the supramolecular gels and the mechanism of the enhancement of fluorescence were investigated. The results are as follows:1. It was found that the optimum concentrations of TC18PheBu and DBS to form supramolecular gels for fluorescence experiment are 2.0 wt% TC18PheBu in pure water and 0.2 wt%DBS in DMSO/H2O(1/2, V/V) mixture solvent. The morphology of supra- molecular gels was observed by POM and FE-SEM. The POM images showed that the aggregates of DBS were spherulite crystalline and the aggregates of TC18PheBu were arborization. The FE-SEM images showed that gelator creates entangled 3D matrix consisting of the bundles of fibrous aggregates.2. The fluorescent spectrum showed that the fluorescence enhanced when the fluorescent molecules were in the supramolecular gels. The fluorescent intensity of fluorescent molecules in supramolecular organogel was double times larger than that in solution when the concentration of DBS was 0.2 wt% and it was 24 times in the supramolecular hydrogel of 2.0 wt% TC18PheBu. The results were confirmed by the variable temperature fluorescence spectra. The fluorescent intensity decreased with the increase of temperature because the supramolecular gel changed into solution.3. The mechanism of the fluorescence enhancement was investigated by using the techniques of inversion fluorescent microscope, fluorescent life times and polarized fluorescence. The fluorescent images showed that the molecules were isolated by 3D matrix of supramolecular gel which could decrease the opportunities of nonradiative process. The results of fluorescent life times showed that the speed of attenuation of fluorescent molecules was lower in supramolecular gels than in solution because the nonradiative process was suppressed to elongate the lifetime.The polarized fluorescence results revealed that the molecular anisotropy of AO was larger in the supramolecular gels than in the solution which was 0.03 in the solution , 0.22 in supramolecular organogel and 0.40 in supramolecular hydrogel. The anisotropy of AO was various with the emission wave numbers suggested that part of AO molecules were in solvent which trapped in gel, others were incorporated in the gel fibers.The molar absorptive and the fluorescence quantum yields of the fluorescent molecules in the same concentration in the solution and in the supramolecular gel were calculated respectively. The molar absorptivity of AO in supramolecular gel and in solution is almost the same, however, the fluorescence quantum yields of AO in supramolecular gels were larger than that in solution, which were 1.1 times and 3.3 times in organogel and in the hydrogel respectively. The results showed that the increase of fluorescence quantum yields leading to the enhancement of fluorescence emission.4. The linear relationship of fluorescent intensity and the concentration of AO were good and the linear correlation coefficient was 0.9999, the recovery was 97.8%, it suggested the fluorescence enhancement induced by gelation can be utilized in the fluorescence analysis in the future.