2010 Volume 23 Issue 2 Pages 217-224
Reversible color imaging on polymer films with a spiropyran (SP-NO2) or a diarylethene (DE) has been examined by electron-beam (EB) induced chromism combined with a photo- or thermal reverse reaction. Colorless SP-NO2 in a poly(methyl methacrylate) (PMMA) film transformed into red-colored zwitterionic merocyanine (MC-NO2), which subsequently converted to the original SP-NO2 via thermal treatment. After six time repetition of the reaction cycle, the absorption intensity of MC-NO2 decreased to 56% of the initial level. The decrease was attributed to the formation of a protonated MC-form (MC-H+) via the reaction of MC-NO2 with an acid generated by EB-radiolysis of PMMA. Contrary to thermal treatment in the polymer films containing SP-NO2, a photo reverse reaction could be applied for EB-induced color imaging using DE in the polymer films, where the thermally stable colored close-form of DE (DECl) obtained by an EB-induced reaction can be converted to the original colorless open-form (DEOP) via photoreaction. The matrix effect of poly(BFP-alt-DOX) was observed with good efficiency of color formation and higher fatigue resistance of DE than those in PSt and PMMA matrices. The color imaging of these films was performed by electron beam direct writing to form 100-1000 nm square and line/space (L/S) patterns. The color images of 5 μm square patterns were produced in the PMMA film containing SP-NO2 with a dose of 100 μC cm-2; the images could be faded upon the thermal treatment. The poly(BFP-alt-DOX) film containing DE yielded clear color imaging of 100 nm L/S patterns with a dose of 200 μC cm-2. Subsequently, the patterns bleached upon the irradiation of visible light of > 430 nm. It is noted that these reactions are the first example for reversible transformation of color imaging induced by EB radiation together with heat or light treatment.
