A guanidine derivative of naphthalimide with excited-state deprotonation coupled intramolecular charge transfer properties and its application

A new fluorophore based on guanidine substituted 1,8-naphthalimide was synthesized and characterized. In aqueous solution, the guanidine group undergoes deprotonation/protonation with a pK(a) of similar to 8.5 in the ground-state and similar to 0.9 in the excited-state. The emission of its protonated and deprotonated forms exhibits a large Stokes shift (Ex/Em: 350/460 nm and 400/580 nm) due to the excited-state intramolecular charge transfer (ICT) process. The protonated form of this fluorophore exhibits dual fluorescence emission (Em: 460 and 580 nm; Ex: 350 nm) that is contributed to by an excited-state deprotonation coupled ICT process. The emission properties of this fluorophore are strongly dependent on the solvent environment, which make it possible to tune the luminescence of the materials made using this fluorophore. The absorption and emission spectra of this fluorophore respond to fluoride ions ratiometrically, showing the potential application as a fluoride ion sensor.