Department of Chemistry, School of Science and Engineering, Aoyama Gakuin University , 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5258, Japan.
Department of Applied Chemistry, College of Life Sciences, Ritsumeikan University , 1-1-1 Noji-higashi, Kusatsu, Shiga 525-8577, Japan.
J Am Chem Soc. 2017 Sep 27;139(38):13429-13441. doi: 10.1021/jacs.7b06293. Epub 2017 Sep 13.
Benzo-annulated chromenes, i.e., naphthopyrans, are well-known photochromic molecules that undergo photochemical ring-opening reactions to form two colored open-ring isomers, the transoid-cis and transoid-trans forms, upon light irradiation. Though the transoid-cis form returns thermally to the uncolored closed form, the fading rate of the transoid-trans form is extremely slow because of its higher thermal stability. This slow fading behavior of the transoid-trans form is responsible for the persistence of residual color for several minutes to hours, and prevents the application of such molecules to fast photoswitching materials. We have found a new simple and versatile strategy to substantially reduce the amount of the undesirable long-lived colored transoid-trans form by introducing an alkoxy group at the 1-position of azino-fused chromenes, i.e., 8H-pyranoquinazolines. The alkoxy group effectively reduces the formation of the transoid-trans form due to C-H···O intramolecular hydrogen bonding in the transoid-cis form. Moreover, the introduction of a condensed aromatic ring at the 3-position was found to be effective to increase the photosensitivity of the ring-opening reaction. This strategy can also be applied for naphthopyran derivatives and is useful for the development of fast photoresponsive photochromic lenses and fast photoswitching applications such as dynamic holographic materials and molecular actuators.
苯并稠合色烯，即萘并吡喃，是众所周知的光致变色分子，它们经历光化学反应开环反应，在光照下形成两种有色的开环异构体，即顺式-反式和顺式-顺式。虽然顺式-反式形式通过热回到无色的闭环形式，但顺式-反式形式的褪色速率非常慢，因为它具有更高的热稳定性。这种顺式-反式形式的缓慢褪色行为是导致残留颜色持续数分钟到数小时的原因，并阻止了此类分子在快速光开关材料中的应用。我们发现了一种新的简单而通用的策略，可以通过在偶氮稠合色烯的 1 位引入烷氧基，即 8H-吡喃并喹唑啉，来显著减少不需要的长寿命有色顺式-反式形式的数量。烷氧基通过顺式-反式形式中的 C-H···O 分子内氢键有效地减少了顺式-反式形式的形成。此外，发现在 3 位引入稠合芳环可以有效地增加开环反应的光敏感性。该策略还可应用于萘并吡喃衍生物，对于开发快速光响应光致变色镜片和快速光开关应用，如动态全息材料和分子致动器非常有用。
