The structural change of a spiropyran (1,3,3-trimethylindolino-8′-methoxybenzopyrylospiran (MBPS)) to ring-opened forms, such as merocyanine and protonated merocyanine, is spontaneously induced in the confined space of a nanoporous silicas. In general, the ring closing of MBPS occurs easily in liquid media under blue-light illumination or under basic conditions. However, the ring-opened forms are tightly fixed and stable in the nanopores of diameters similar of the molecules owing to the hydrogen-bonding with silanol groups and the strong steric-restriction. The color of the ring-opened forms in the confined space varies with the protonation; therefore, the MBPS trapped in the nanoporous silica with open pores is sensitive to the pH of the surrounding solution.

中文翻译：

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纳米多孔二氧化硅有限空间中螺吡喃的稳定开环形式

螺吡喃（1,3,3-三甲基吲哚啉-8′-甲氧基苯并吡咯螺烷（MBPS））向开环形式（例如部花青和质子化部花青）的结构变化是在纳米多孔二氧化硅的有限空间中自发诱导的。一般来说，在蓝光照射或碱性条件下，MBPS在液体介质中很容易发生闭环。然而，由于与硅烷醇基团的氢键作用和强烈的空间限制，开环形式在与分子直径相似的纳米孔中被紧密固定和稳定。密闭空间中开环形式的颜色随质子化而变化；因此，被捕获在具有开孔的纳米多孔二氧化硅中的MBPS对周围溶液的pH值敏感。