Cystine-derived bis-naphthalimides as stimuli-responsive fluorescent gelators

Abstract

Two cystine-derived bis-naphthalimide gelators (L1, L2) were synthesised and characterised. Both L1 and L2 exhibited similar absorptions and emission spectra in solvents such as acetonitrile and DMF. The fluorescence spectra of both the compounds featured a distinct monomer and long-wavelength excimer emissions in the aforementioned solvents. It was found that the excimer emissions for the two compounds could be preferentially quenched by triethylamine, and subsequently restored with hydrofluoric acid. The stimuli-responsive nature of the excimer emissions was demonstrated using anion stimuli in solution and in the gel phase. Thus, the excimer emission for L1 (or L2) could be switched ‘off’ using fluoride anions, and subsequently re-activated using tetrafluoroborate anions as the chemical stimulus.