Creating a Vision for Photochromic and Chiral Helicenoid Diarylethenes

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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.