Extensive spectral tuning of the proton transfer emission from green to red via a rational derivatization of salicylideneaniline

A series of salicylideneaniline derivatives 1a-lf were synthesized under mild condition in high yields, and characterized by ^1H NMR, HRMS, UV-vis and emission spectra. In solid and aprotic solvents 1a-1f exist mainly as E conformers that possess a sixmembered-ring hydrogen bond and undergo excited-state intramolecular proton transfer （ESIPT） reactions, resulting in a protontransfer tautomer emission. Depending on the electronic donor or acceptor strength of the substituent in either the HOMO or LUMO site, a broad tuning range of the emission from green （1c） to red （1a） has been achieved.