Photochromic properties of cationic merocyanine dyes. Thermal stability of the spiropyran form produced by irradiation with visible light
作者:Shigeyuki Yagi、Katsumi Maeda、Hiroyuki Nakazumi
DOI:10.1039/a905098a
日期:——
A series of novel cationic merocyanine dyes were prepared by condensation of 1,2,3,3-tetramethylindolium derivatives and 3-formyl-4H-1-benzothiopyran or -benzopyran derivatives, and their photochromic properties were investigated, especially focusing on the substituent effect in the indolium moiety. These dyes were converted into the spiropyran (SP) form so as to be colorless by irradiation with visible light, although, left under darkness, the colored merocyanine (MC) form was reproduced. The thermal coloration was affected by two factors: the substituent in the indolium moiety and the counter anion. An electron-donating substituent such as a methoxy group at the 5 position effectively retarded the thermal coloration, whereas an electron-withdrawing group such as a nitro group accelerated it. These substituent effects afforded good linearity for the Hammett rule with para σ parameters, indicating that decrease of the electron density in the indoline moiety of the SP form facilitated heterolytic cleavage of the bond between the spiro carbon and the oxygen of the pyran ring.
通过缩合反应制备了一系列新型阳离子型部花青染料,该反应涉及1,2,3,3-四甲基吲哚鎓衍生物与3-醛基-4H-1-苯并噻吡喃或苯并吡喃衍生物的反应,并研究了它们的光致变色性质,特别关注吲哚鎓部分中的取代基效应。这些染料在可见光照射下转化为无色的螺吡喃(SP)形式,尽管在黑暗环境中,带色的部花青(MC)形式会再次出现。热致变色受到两个因素的影响:吲哚鎓部分的取代基和反荷离子。在5位带有供电子取代基(如甲氧基)有效地延缓了热致变色,而吸电子基团(如硝基)则加速了热致变色。这些取代基效应提供了良好的Hammett规则线性关系,对应于para σ参数,表明在SP形式中吲哚部分电子密度降低促进了螺碳与吡喃环氧之间键的异裂解离。