Self-Assembly Controls Reactivity with Nitric Oxide: Implications for Fluorescence Sensing

Three molecules containing the fluorophore 4-amino-1,8-naphthalimide (ANI) and showing different tendencies to self-assembly in aqueous environment have been prepared and fully characterized. The fluorescence emissions of two of these compounds in aqueous solutions are efficiently quenched in the presence of nitric oxide (NO) in aerated medium. Nuclear magnetic resonance and mass spectrometry techniques indicate that NO/O₂ induces deamination of the ANI fluorophore, resulting in nonemissive 1,8-naphtalimide derivatives. It is found that the reactivity toward NO/O₂ is regulated by the different aggregation modes presented by the molecules in aqueous medium. In this way, the molecules displaying fluorescence response toward NO/O₂ are those with weak self-association properties whereas the compound with a high hydrophobic character (self-assembling into large nanoparticles) is insensitive to this species. Ultimately, the results described here could not only set the basis for the design of fluorescent bioprobes for NO/O₂ based on ANI derivatives or other monoamino compounds but also could raise awareness about the importance of supramolecular interactions for the design of chemosensors.