A Self-Assembled Peptide-Appended Naphthalene Diimide: A Fluorescent Switch for Sensing Acid and Base Vapors

A histidine-containing bola-amphiphilic molecule (NDIP) containing a peptide-appended naphthalenediimide (NDI) forms fluorescent hydrogels in phosphate buffer and organogels with benzenoid solvents. These gels were characterized by several spectroscopic and microscopic techniques including FT-IR, HR-TEM, powder X-ray diffraction and small-angle X-ray scattering, UV-Vis and fluorescence studies. The gelator molecule exhibits no significant fluorescence in the xerogel state, while it shows a significant fluorescence (bright cyan) in the presence of volatile organic/inorganic acid vapors; this cyan color vanishes in presence of base (ammonia vapors). A reusable paper-strip-based method based on this self-assembled fluorescent material can be used to easily detect hazardous volatile acid and base vapors with the naked eye.