Design, Synthesis And Gelation Properties Of Some Low Molecular Weight Gelators

In this work, a bi-component gelator (PM) of melamine with di(2-ethylhexyl)phosphoric acid, a charge transfer gelator (A+D) consisting of2,4-(4-nitro-benzylidene)-D-sorbitol (compound A) and2,4-(4-amino-benzylidene)-D-sorbitol(compound D) and salen-appended sorbitol gelator were synthesized. All of themwere new compounds.The gelation ability of the bi-component gelator (PM) was evaluated. PM canform metastable hydrogel in pure water and stable mixed-hydrogels in organic-watermixtures. According to the gel sol transition temperature, SEM and rheologicalproperties, the morphologies of the aggregates and the thermodynamic properties ofthe gel depended on the composition of the solvent where they were formed. FT-IR,31P NMR and XRD studies showed that intermolecular hydrogen bonding was themain driving force for the formation of the supramolecular gel. The gelation tests andthe Flory-Huggins interaction parameter can serve as a model to predict the gelationbehavior of PM in a range of solvents. This predictive tool was further tested byanalyzing data from gelation tests reported in the literature.The gelator (A+D) consisting of2,4-(4-nitro-benzylidene)-D-sorbitol and2,4-(4-amino-benzylidene)-D-sorbitol can form stable gels in a variety of organicsolvent. UV absorption spectra showed that the charge transfer interactions occuredduring the gel formation. SEM and XRD showed that the morphologies of theaggregates can be changed by charge transfer interaction. Based on this, a possiblestacking patterns were obtained.2,4-(4-(2-hydroxy naphthalen imino)-benzylidene)-D-sorbitol (compound S1)was used as a low molecular weight gelator for the study of self-assembly,multiple-stimuli responsive properties and photophysical properties. Compound S1not only can form stable gels at room temperature but also can form gels by thestandard heating-cooling method. POM and SEM showed the existence of thethree-dimensional gel network structure, UV absorption spectra, fluorescenceemission spectra and1H NMR studies showed that the fluorescence enhancement ofthe gel was due to the formation of J-aggregates by π-π stacking interactions and therestriction of molecular movement in the gel state. Compound S1containing sorbitolmoiety and naphthalene-based salicylideneaniline group exhibited macroscopic reversible gel-sol behavior in response to four complementary input stimuli:temperature, UV/Vis, H+/OH-, and Cu2+/EDTA. Hence, the intelligent gel softmaterial was prepared based on compound S1. On the basis of its multiple-stimuliresponsive properties, we constructed a rational gel-based supramolecular logic gatesfrom compound S1that performed OR, INH and composite INH types of reversiblestimulus responsive gel-sol transition in the presence of various combinations of thefour stimuli when the gel state was defined as an output.