Modular functional integration of a two-input INH logic gate with a fluorophore-spacer-receptor1-spacer-receptor2 conjugate

The synthesis and photophysical characterization of a fluorophore-spacer-receptor(1)spacer-receptor(2) system, which combines the 1,8-naphthalimide fluorophore with amine and urea receptor units, is reported. Photoinduced electron transfer (PET) from the amino group was blocked by protonation, leading to a drastic fluorescence enhancement (ca. 20 times). Interaction of the urea receptor with anions (F-, AcO-, H2PO4-) via hydrogen bonding or urea NH deprotonation resulted in significant fluorescence quenching of the 1,8-naphthalimide chromophore in an appropriately chosen model compound (ca. 30-45%). In the presence of both chemical input species, protons and anions, the fluorescence was also quenched. The binding of the anions by NH+ ammonium receptor has been assumed. The apparent anion binding constants of the protonated conjugate follow the basicity trend of the anions: AcO- similar to F- > H2PO4-. The investigated system constitutes an example for the flexible and modular realization of functionally integrated INH logic at the molecular level, using protons and anions as chemical input species and the fluorescence of a PET-active signaling unit as output.