Photochromic complexes based on enantiomeric 2-(4-pyridyl)-4, 5-dihydrothiazole-4-carboxylic acids

Abstract New enantiopure ligands, (R)-/(S)-2-(4-pyridyl)-4,5-dihydrothiazole-4-carboxylic acids (HL R , HL S ) were synthesized, subsequently their reactions with Cd(ClO 4 ) 2 ·6H 2 O resulted in the formation of complexes [CdL R 2 (H 2 O) 2 ]·3H 2 O ( 1R ) and [CdL S 2 (H 2 O) 2 ]·3H 2 O ( 1S ). The structure of 1R was determined by single crystal X-ray diffraction analysis. The complexes show instant colour change upon irradiation with UV light. The photochromic mechanism is investigated by ESR and UV-Vis spectroscopic techniques. The results indicate that the photochromic transformation is originated from the formation of the free radical.