In this study, we show that a novel kind of cholesterol-based gelator NPS containing pyridyl and naphthalimide units can visually discriminate cyclohexane/cyclopentane from hexane/pentane on the basis of distinct optical differences in the gel platform, which is not observed in solution. The effect of congeneric solvents on the gel properties, such as morphology, rheology, and stimuli-responsive properties, is also studied. Intriguingly, NPS can form self-supporting, self-healing, fluorescent, and highly visible transmittance gels in cyclohexane that can selectively and visually respond to picric acid. It is deduced that NPS adopted H-type aggregation mode in cyclohexane, and the gel exhibits a strong green emission, whereas, in hexane, J-type aggregates of NPS molecules are observed with yellow emission. Correlations between the gelation properties and Hansen solubility parameters indicate that the dispersion interactions are the main factor for the selective gelation of NPS toward short-chain alkanes. A comparison of Hansen solvent parameters indicated that a similar energetic weight of the hydrogen-bonding units is the major contribution for the strong and specific interaction between NPS and cyclohexane. Furthermore, we demonstrated that the NPS xerogel can selectively solidify cyclohexane in the single-phase liquid of solvent mixtures, exhibiting fast gelation, high separation efficiency (>92%), and easy recycling of gelator and liquids. To the best of our knowledge, herein, we report the first paradigm that molecular gel formation is developed to visually discriminate and separate organic analogues of solvents with similar polarity.
Keywords: fluorescence; isomer recognition; molecular gel; self-healing; stimuli-responsive material.