A novel pillar[5]arene-based supramolecular organic framework gel to achieve an ultrasensitive response by introducing the competition of cation⋯π and π⋯π interactions

Abstract

Ultrasensitive response properties are an intriguing concern for stimuli-responsive materials. Herein, we report a novel method to achieve an ultrasensitive response by introducing the competition of cation⋯π and π⋯π interactions into a pillar[5]arene-based supramolecular organic framework (SOF-AMP). SOF-AMP was constructed with a novel bis-naphthalimide functionalized pillar[5]arene, which was able to form a stable supramolecular gel (SOF-AMP-G) in cyclohexanol. Interestingly, SOF-AMP-G shows an ultrasensitive response to Fe³⁺ through the competition of cation⋯π and π⋯π interactions. Meanwhile, the Fe³⁺ coordinated SOF (MSOF-Fe) shows an ultrasensitive response to H₂PO₄⁻. SOF-AMP-G displayed yellow fluorescence whereas, after the addition of 0.5 equiv. of Fe³⁺ to SOF-AMP-G, the yellow fluorescence was quenched. The detection limit of SOF-AMP-G for Fe³⁺ is 7.54 × 10⁻⁹ M. More interestingly, the Fe³⁺ coordinated SOF gel (MSOF-Fe-G) could sense H₂PO₄⁻ with a fluorescence “turn-on”. The detection limit of MSOF-Fe-G for H₂PO₄⁻ is 4.21 × 10⁻⁹ M. Simultaneously, the Fe³⁺ and H₂PO₄⁻ responsive thin films based on these SOF gels were prepared. Moreover, these SOF gels could be used as ultrasensitive ion sensors, fluorescent display materials and sensitive logic gates.