Naphthalimide-based fluorescent Zn2+ chemosensors showing PET effect according to their linker length in water

We have developed naphthalimide-based fluorescent chemosensors that exhibit fluorescence enhancement upon binding Zn2+ ion in 10 mM HEPES buffer (pH 7.4) at 25 °C. The fluorescence enhancement was induced by a PET inhibition process in which electron transfer from the nitrogen lone pair electrons of the Dpa unit to naphthalimide was blocked upon the binding of the sensor to Zn2+. The longer the linker length (n = 1–3) of the sensor, the less the PET efficiency becomes. Among the sensors (1, 2, and 3) examined, 1 shows the highest selectivity and sensitivity for Zn2+ over other transition metal ions and alkali metal ions in water.