含三氯化铁的紫精/聚合物薄膜的光致变色性能和机理研究

Photochromic property and mechanism of a viologen film containing ferric chloride

紫精/聚合物薄膜光照后产生颜色变化,但褪色缓慢,加入过渡金属离子可以促进薄膜褪色。制备了一种含有三氯化铁的紫精/聚乙烯吡咯烷酮(PVP)光致变色薄膜。三氯化铁的加入消耗薄膜中光照产生的自由基阳离子,使薄膜的颜色变浅,但褪色加快,薄膜的光致变色随着变色/褪色的增加而加深,当三氯化铁和紫精的摩尔比为1∶1时,经过3次变色/褪色循环后,薄膜光照后变色较深,并可褪色至无色;改变三氯化铁的含量和褪色温度,可以调节褪色速率。X射线光电子能谱(XPS)结果表明,光照后的三氯化铁/紫精薄膜中既有Fe+3也有Fe+2,由此提出可能的变色机理为Fe+3从紫色的紫精自由基阳离子夺取电子变成Fe+2,而紫精退回到无色的二价阳离子态。

Photochromic viologen/polymer blended films exhibit obvious coloring when exposed to UV light.The bleaching process of the colored film,however,is rather slow.Bleaching can be promoted by addition of transition metal ions into the blended films.A photochromic film composed of ferric chloride and viologen/polyvinylpyrrolidone is prepared in this work.Ferric chloride destroyed the radical cations from the photoreduced viologens in the film,and makes the color of the film lighter with increased bleaching rate.The color of the photochromic films gradually becomes deeper with increasing times of repeated coloring/bleaching cycles.The blended film with mole ratios of ferric chloride to viologen in 1∶1 after three times of cycles showed deeper coloring can be deeply colored when exposed to UV light,and bleached to colorless after repeated cycles of coloring/bleaching.Bleaching of the blended film is adjustable by the concentration of Fe2＋ and the temperature of bleaching.The results of XPS spectra indicate that there exist both Fe2＋ and Fe3＋ in the blended film after exposing to UV light.A mechanism for the photochromic process is proposed：Fe3＋ Abstracts electron from the radical cation of the photoreduced viologen and becomes the redued Fe2＋ while the photoreduced viologen returns back to the colorless oxised state.