Photo responsive dyads for fast recognition of cyanide and fluoride in aqueous media

Three new photo responsive molecular dyads have been synthesized by the reaction of 4-hydrazino-N-benzyl-1,8-naphthalimide with different diketone derivatives (benzil, acenaphthene quinone, pyrene-4,5-dione). Naphdiones have been observed to exhibit photo tautomerization plausibly due to proton transfer from the 4-aminonaphthalimide, -NH to the carbonyl, >C=O moiety of the dione when photo-irradiated in a polar aprotic solvent (THF). The synthesized dyads also respond to protonation and de-protonation on change of pH of the medium and exhibited well defined multi-colour solvatochromism in different solvents. The synthesized derivatives have been determined to be highly sensitive towards critical anions (e.g., fluoride and cyanide ions). Observed photo tautomerization has been confirmed by DFT calculations and solvent induced spectral changes. The recognition of cyanide and fluoride in dilute solutions has been observed to be very fast and required less than 15 s response time. Mechanism of interaction has been confirmed through H-1 NMR and UV-Vis spectra. Details of experiments conducted, energy calculations and spectral observations made for ionic recognition have been described.