A comparison of the solution and solid state thermal decay kinetics of five photochromic spiropyrans with different N-alkyl groups (SP1–SP5) was carried out in acetonitrile and nanocrystalline suspensions at 298 K. The change in absorbance at ca. 550 nm was measured as a function of time for the merocyanine (MC) using transmission UV–vis spectroscopy. We found that the thermal decay kinetics are slower and follow a biexponential decay in the solid state compared to a faster, monoexponential decay that was measured in solution. We observed that, while the kinetic range measured in solution varies by a factor of 13, the decay kinetics in the solid state cover a range of ca. 150, indicating that crystal packing has an influence much greater than that of the effects of N-alkyl substitution. A fluorescence analysis of irradiated samples of SP1 in solution could be used to determine the formation of the MC species and its subsequent decay. By contrast, a similar analysis of nanocrystalline suspensions displayed changes as a function of time that are consistent with self-quenching.
在 298 K 的
乙腈和纳米晶体悬浮液中,对具有不同 N-烷基的五种光致变色螺
环丙烷(
SP1-
SP5)的溶液和固态热衰减动力学进行了比较。我们使用透射紫外可见光谱法测量了美拉西
氨酸(MC)在 550 纳米波长处的吸光度随时间的变化。我们发现,与在溶液中测量到的较快的单指数衰减相比,固态下的热衰减动力学较慢,且遵循双指数衰减。我们观察到,在溶液中测得的动力学范围相差 13 倍,而在固态中的衰变动力学范围约为 150 倍,这表明晶体堆积的影响远远大于 N-烷基取代的影响。对溶液中经过辐照的
SP1 样品进行荧光分析,可以确定 MC 物种的形成及其随后的衰减。相比之下,对纳米晶体悬浮液的类似分析显示出与自淬相一致的随时间变化的变化。