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

A series of salicylideneaniline derivatives 1a–1f 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 six-membered-ring hydrogen bond and undergo excited-state intramolecular proton transfer (ESIPT) reactions, resulting in a proton-transfer 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.