Functional organogel based on a hydroxyl naphthanilide derivative and aggregation induced enhanced fluorescence emission

Abstract

A new class of low molecular weight organogelator (LMOG) of hydroxyl naphthanilide moiety was suitably designed and synthesized and it forms gels through noncovalent interactions in hydrocarbon solvents. Self-assembly structure, hydrogen bonding interaction, and photophysical properties of organogelator 3-hydroxy-naphthalene-2-carboxylic acid (2-heptylcarbamoyl-phenyl)-amide ( 2) have been investigated by field emission scanning electron microscope (FE-SEM), FT-IR, UV–vis absorption and photoluminescence combined with theoretical studies by hybrid density-functional theory (DFT) B3LYP and semi-empirical calculations AM1 with CI methods. It was found that gelation is completely thermoreversible, and it occurs due to the aggregation of the organogelator resulting in the formation of a fibrous network due to the π–π stacking interaction complemented by the presence of both inter- and intra-molecular hydrogen bonding. The self-assembled fibrillar networks in the gels were distinctly evidenced by SEM observations. FT-IR studies confirm that the common driving force for aggregation in the organogels and microsegregation in the mesophase is the occurrence of a tight intermolecular hydrogen bonded network that does not persist in diluted solution. Gelator 2 is very weakly fluorescent in solution, but its intensity is increased by almost 30–32 times in their respective gelled state depending on the nature of the gelling solvents. The aggregation induced emission enhancement is ascribed to the formation of J-aggregation and inhibition of intramolecular rotation in the gel state.