Tunable far-red fluorescence utilizing π-extension and substitution on the excited state intramolecular proton transfer (ESIPT) of naphthalene-based Schiff bases: A combined experimental and theoretical study

•Naphthalene-based Schiff bases with two hydrogen bonds have been synthesized.•Photophysical properties are controlled by chemical modifications.•Far-reded keto emission is induced by electron-withdrawing group.•A Schiff base with large Stokes shift is potential for fluorescent probes.