Molecular doping of photochromic dye into polymer substrates by the “vapor transportation method” and their photochromic behavior

Photochromic dye, cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)ethene (CMTE) was doped into poly(methyl methacrylate) (PMMA) and polystyrene (PS) using a simple vacuum process, named the vapor transportation method (VTM), which can form functional molecule-doped regions on polymer substrates. Photochromic behavior of CMTE into these polymer substrates was observed by UV-vis absorption spectroscopy. When UV light was irradiated to CMTE-doped polymer films, their color changed from light yellow (open ring form) to reddish brown (closed ring form), indicating that CMTE molecules keep their own photochromic properties inside the polymers. After UV light was irradiated to CMTE-doped PMMA films formed by the VTM, CMTE conversion efficiency of the films was higher than that of CMTE-doped PS films formed by the VTM. After UV light was irradiated to PS and PMMA films with CMTE doped by the VTM, CMTE conversion efficiency of the films was higher than that of PS and PMMA films with CMTE formed by the casting method. This indicates that a photochromic behavior of the PS and PMMA films formed by VTM is better than those formed by the casting method.