Self-assembly and gelation of benzylidene sorbitol derivatives in organic solvents

Abstract

The self-assembly and gelation of benzylidene sorbitol derivatives, 1,3:2,4-di-O-benzylidene-Dsorbitol (DBS), 1,3:2,4-di-O-p-methylbenzylidene-D-sorbitol (MDBS) and 1,3:2,4-di-O-m,p-dimethylbenzylidene- D-sorbitol (DMDBS) as gelators were investigated based on their molecular structure, solvophilic effect, enthalpies of phase transition and the polarity of solvents. Structural differences among the three gelators are only in the varied amount of methyl groups on the benzene ring. It was found that the ability of self-assembly for the three gelators was related to the amount of methyl groups. The lower minimum gelation concentration (MGC) and higher phase transition temperature for MDBS and DMDBS usually imply higher ability of self-assembly due to the more methyl groups in comparison with DBS. The large polarity of solvents causes decrease of phase transition temperature of the gels formed by these three gelators. Polarized optical images of the gels show that the aggregates of the three gelators are spherulite crystallite and other types of crystallite in n-octanol. FE-SEM images show entangled fiber-like aggregates of the gelators, which in turn form a three-dimensional network in n-octanol gels. UV spectra of the n-octanol gels formed by the three gelators indicate that the K bands of benzene rings are red shifted. It reveals that the π-π stack is one of the driving forces for the self-assembly of the gelators. The extent of red shifts of K bands depends on the amount of methyl groups in benzene rings which is in accord with the stabilities of the gels formed by such three gelators.