Synthesis of a low-molecular-weight fluorescent ambidextrous gelator: development of graphene- and graphene-oxide-included gel nanocomposites

Abstract

Low-molecular-weight fluorescent supramolecular ambidextrous gelators have drawn enormous attention owing to their ever-increasing number of potential applications. In this study, we synthesized a low-molecular-weight fluorescent ambidextrous gelator consisting of hydrophobic pyrenebutyric acid moieties at the N termini of a central l-lysine, and an ethyleneoxy unit coupled with 1-(3-aminopropyl)imidazole via a succinic acid linker as a hydrophilic moiety at the C terminus. This compound showed efficient hydrogelation and organogelation, having minimum gelation concentrations of 0.5 % (w/v) in a DMSO/water mixture (1:4 v/v) and 0.2 % (w/v) in nitrobenzene. The presence of the pyrene moieties in the structure rendered the ambidextrous gelator fluorescent. Significant amounts of both graphene oxide and reduced graphene oxide were included within these gels to form a stable soft nanohybrid. Hydrogen bonding, π–π stacking and van der Waals interactions are the key factors for self-assembly leading to gelation. The complementary interactions between the π-electronic surface of 2D graphene sheet and the aromatic pyrene moieties of the gelator play key roles in the inclusion of the nanomaterials into the gels. The inclusion of carbon nanomaterials within the gels resulted in a notable improvement in the stiffness of the soft nanocomposites compared to native gels. The native gels and soft nanocomposites have shear thinning properties and are thixotropic in nature.