A Schiff base with excited-state intramolecular proton transfer and its Zinc(II) complex: Mechanochromic luminescence and acid-base stimuli response.

A novel Schiff base ligand HL ·CH 3 COOH with excited-state intramolecular proton transfer (ESIPT) and its zinc (Ⅱ) complex 1 were successfully synthesized, and both of them show high-contrast mechano- and acidochromic luminescence. [Display omitted] A new Schiff base compound (HL ·CH 3 COOH) with D-A structure and its zinc(II) complex (1) were successfully obtained. Due to the introduction of diethylamino and rotatable aromatic rings, both HL ·CH 3 COOH and the complex adopt loosely packing patterns. HL ·CH 3 COOH exhibits keto-form emission due to the excited-state intramolecular proton transfer (ESIPT) process, while complex 1 shows enol-form emission. They all show reversible mechanochromic luminescence (MCL) behavior, which is caused by the phase transformation from crystalline state to amorphous state revealed by Powder X-ray diffraction (PXRD) studies, and is accompanied by the departure of CH 3 COOH molecules for HL ·CH 3 COOH. HL ·CH 3 COOH and complex 1 can be protonated under the fumigation of HCl, resulting in the acidochromic properties, accompanied with the phase transformation. HCl also destroyed the interactions between CH 3 COOH and Schiff base molecules, leading to the departure of acetic acid molecules. More interestingly, HL ·CH 3 COOH also exhibited NH 3 -stimuli response properties due to the prohibition of the ESIPT process. [ABSTRACT FROM AUTHOR]