Isomerization of spirobenzopyrans bearing electron-donating and electron-withdrawing groups in acidic aqueous solutions
作者:Taku Satoh、Kimio Sumaru、Toshiyuki Takagi、Katsuki Takai、Toshiyuki Kanamori
DOI:10.1039/c0cp01989e
日期:——
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。