Photochromic molecules, which undergo reversible photoinduced isomerization reactions, have been investigated from various viewpoints of basic chemistry and application to photonic devices such as optical memories, switches, and so on. Moreover, various new properties accompanied with photochromic reactions in crystalline phase have been reported in these years. For example, Irie and co-workers reported that a single crystal of a diarylethene (DAE) derivative, which shows reversible ring-closing and ring-opening reactions, exhibited rapid and reversible macroscopic changes in shape and size could be induced by UV and visible light irradiations. In the present paper, a new system which exhibits drastic change of the surface wettability is reported for a crystalline solid of photochromic diarylethene derivatives (DAE). This new functionality was attributed to the photoinduced reversible changes in surface morphology of the crystal via the photochromic reactions. SEM and optical microscope images revealed that the phase separation of the closed-ring isomer produced by the UV light irradiation of the molecular crystal of open-isomers plays an important role in this function. That is, closed-ring isomers produced by the UV irradiation form many microcrystals with fibril structures on the surface through the phase separation, leading to the appearance of the superhydrophobicity as on the leaves of the lotus. This superhydrophobicity disappeared upon irradiation of the surface with visible light owing to the ring-opening reaction leading to the disappearance of these micro fibril structures. In the presentation, the details of the mechanisms will be introduced.
可逆的な光誘起異性化反応であるフォトクロミズムを示す分子系は、光メモリーや光スイッチなど、また光照射によって単結晶の形状自体も変形する特性を利用したメゾスコピック光駆動アクチュエーターへの展開を含め、多くの研究がなされるとともに、新規物性の報告もなされている。 本論文では、環開閉反応によりフォトクロミズムを示す代表的な分子系であるジアリールエテンの開環体単結晶の表面が、光照射に伴うフォトクロミック反応によって、撥水性の大きな変化を示すことを報告している。結晶表面の電子顕微鏡画像や光学顕微鏡画像から、紫外光照射によって生じた閉環体が表面近傍において相分離を起こし、表面に閉環体の針状微結晶が現れることが、このような撥水性の変化が生じる原因であることを明らかにしている。 発表では、得られた結果とその解釈について詳細に報告する予定である。