Photochromic properties of spiropyran in epoxy resin as anti-counterfeiting coating on flexible materials

A kind of spiropyran derivatives, 1-chloro-3-(3′,3′-dimethyl-6-nitrospiro[chromene-2,2′-indolin]-1′-yl)propan-2-ol (CSP), was synthesized and characterized by FT-IR, 1H NMR, EI-MS, which contained the spiropyran moiety. The photochromism and solvatochromism in the diverse solvents were investigated in details. The polarity of the solvent played a crucial effect on the absorbance of the ring open form (MC) for CSP, characterized by using the relative polarity and Reichardt's empirical solvent polarity parameter (ET(30)). The fatigue resistance was evaluated by the number of cycles required to reduce the initial absorbance at λmax by 50% (Z50). Entrapment of the radical-scavengers such as butylated hydroxyl toluene (BHT) and 2,2,6,6-tetramethyl-piperidine-1-oxyl (TEMPO) practically enhanced the duration of CSP and protected most of the molecules from further oxidation in acetone. The parameter Z50 in ethyl acetate was 534 and was much higher than the others. However, it reached to more than 1200 when CSP was doping in the epoxy resin on OPP film. It indicated that the CSP could be applied in the flexible substrate for foods and medicine package.