A Cu2+ protein cavity mimicking fluorescent chemosensor for selective Cu2+ recognition: tuning of fluorescence quenching to enhancement through spatial placement of anthracene unit

Four new fluoroionophores possessing four ligating sites (2S+2N) and an essential hydrophobic environment, as prevailing in the plastocyanin and rusticyanin proteins, have been synthesized. In these PET fluoroionophores, the position of fluorophore anthracene moiety effectively modulates the Cu2+ induced emission properties (quenching vs enhancement) of the fluorophore. The addition of Cu2+ to solution of receptor with anthracene moiety in its center caused quenching in emission intensity through photoinduced fluorophore-to-metal electron transfer mechanism and in cases where anthracene is present at terminus nitrogen, the emission intensities increased by nearly 1000% due to inhibition of the photoinduced electron transfer from receptor-to-fluorophore in the presence of Cu2+ ions. The hydrophobic environment created by various aromatic rings clearly manifested the stability of fluorescence of these molecules above pH 2.0 and their Cu2+ complexes above pH 4. The application of such fluoroionophores has been elaborated for building OR and AND logic gates.