Pieraccini Silvia, Gottarelli Giovanni, Labruto Riccardo, Masiero Stefano, Pandoli Omar, Spada Gian Piero
Alma Mater Studiorum, Università di Bologna, Dipartimento di Chimica Organica A. Mangini, Via San Giacomo 11, 40126 Bologna, Italy.
Chemistry. 2004 Nov 5;10(22):5632-9. doi: 10.1002/chem.200400463.
A few chiral azo compounds, which undergo reversible photochemical switching, are presented. Of these, the most interesting contain the binaphthyl moiety and belong to the C2 (derivatives 1 and 2) or C1 symmetry group (derivatives 3 and 4). These binaphthyl compounds display intense CD and high beta values. Photochemical switching has profound effects on both the CD and beta values of these compounds; in the case of compound 3, the sign of beta changes upon isomerisation. Compound 2 has, to our knowledge, the highest beta of the switches reported in the literature and also seems the most interesting owing to its fast response to photochemical stimuli. Nematic phases can be transformed into cholesteric phases with reflection bands in the visible region by doping with reasonable amounts of 1 and 2. The reflection colours can be changed reversibly by photoisomerisation of the switches. Thermal reversion of the colourless UV photostationary state to the green isomeric EE state or to intermediate coloured states is temperature dependent. This can allow the thermal history of a sample to be traced.
本文介绍了几种可进行可逆光化学开关的手性偶氮化合物。其中，最有趣的是含有联萘部分的化合物，它们属于C2对称群（衍生物1和2）或C1对称群（衍生物3和4）。这些联萘化合物表现出强烈的圆二色性（CD）和高的β值。光化学开关对这些化合物的CD和β值都有深远影响；对于化合物3，异构化时β的符号会发生变化。据我们所知，化合物2具有文献报道的开关中最高的β值，并且由于其对光化学刺激的快速响应，似乎也是最有趣的。通过掺杂适量的1和2，向列相可以转变为在可见光区域具有反射带的胆甾相。反射颜色可以通过开关的光异构化可逆地改变。无色紫外光稳态向绿色异构体EE态或中间颜色状态的热反转取决于温度。这可以用于追踪样品的热历史。
