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

摘要

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 AMI 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.