Creating a Vision for Photochromic and Chiral Helicenoid Diarylethenes

已知螺烯具有较大的比旋光度。为了引起旋光度的较大变化，需要进行非对映选择性的光致变色反应。我们选择了用一个简单的手性助剂连接到闭环的己三烯部分来诱导非对映选择性光致变色反应。然后，我们合成了六个在C-3或C-2与全氟环戊烯相连的手性螺烯二芳基乙烯。我们研究了这六种分子的光化学行为，特别是光致变色中的非对映选择性。在这些研究过程中，我们可以对二芳基乙烯的非对映选择性与取代基(甲氧基和甲氧基)的关系进行有益的考察，从而在光致变色性中获得较大的旋光度变化。也就是说，我们发现这些分子中两个取代基之间的空间排斥和电子排斥以及甲氧基和苯并噻吩基之间的电子排斥是很重要的。

Helicenes are known to show large specific optical rotation. In order to induce a large change in optical rotation, a diastereoselective photochromic reaction should take place. We chose to induce a diastereoselective photochromic reaction with a simple chiral auxiliary attached to the ring-closing hexatriene moiety. Then, we synthesized six chiral helicenoid diarylethenes having the aromatic group connected to perfluorocyclipentene at C-3 or C-2. We examined the photochemical behaviors of these six molecules, especially about the diastereoselectivity in photochromism. In the course of these investigations, we could gain the useful inspection about the relation between the diastereoselectivity and the substitution groups (methoxyl group and methoxymethoxyl group) in diarylethenes to obtain large optical rotation changes in photochromism. That is, we found the steric and electronic repulsion between two substitution groups and the electronic repulsion between the methoxyl group and benzothiophen moiety in these molecules were important.