Origins of ‘on–off’ fluorescent behavior of 8-hydroxyquinoline containing chemosensors

Derivatives of 8-hydroxyquinoline were used as model compounds to probe the pathways of non-radiative relaxation of fluorophores in two fluorescent chemosensors. Results suggest that both photo-induced proton transfer and photo-induced electron transfer contribute to quenching the fluorescence of the chemosensors. Crystal structures of an 8-hydroxyquinoline-containing chemosensor complexed to various metal ions indicate that a proton shift occurs concomitant with complex formation. This proton shift precludes both photo-induced proton and electron transfer allowing fluorescence emission from chemosensor-metal ion complexes.