Spirobenzopyrans, which are well known as photochromic compounds, exist as thermodynamically stable protonated ring-opened isomers (protonated merocyanine form, McH) in an acidic aqueous solution in the dark. In the present study, we investigated effects of substitution of the spirobenzopyrans on a ring-opening behavior in an aqueous system. We prepared five polymerizable spirobenzopyrans that are substituted with a methoxy group or a nitro group at the 6′- or 8′-positions and without a substituent. These monomers were copolymerized with N,N-dimethylacrylamide to evaluate the spirobenzopyrans in aqueous solution. Correlation between ring-opening rates and the kind and position of the substitution can be summarized as follows: the substitution of an electron-donating methoxy group and the substitution at the 8′-position increased the ring-opening rate, whereas the substitution of an electron-withdrawing nitro group decreased the rate. The effects of the substitution can be explained by changes in the electron density of the oxygen atom of the spirobenzopyrans.
螺苯并
吡喃是众所周知的感光化合物,在黑暗中以热力学稳定的质子化环开异构体(质子化
亚甲基蓝形式,McH)的形式存在于酸性
水溶液中。在本研究中,我们研究了螺苯并
吡喃取代对
水溶液中环开行为的影响。我们制备了五种可聚合的螺苯并
吡喃,它们在6′-或8′-位置被甲氧基或硝基取代,且没有取代基。这些单体与N,N-二甲基
丙烯酰胺共聚,以评估
水溶液中的螺苯并
吡喃。环开速率与取代的种类和位置之间的相关性可以总结如下:电子给体甲氧基的取代和8′-位置的取代增加了环开速率,而电子吸引体硝基的取代降低了环开速率。取代的影响可以用螺苯并
吡喃氧原子的电子密度变化来解释。