Relations of the structures and the reactivities of Photochromic Diarylethenes.

二芳基乙烯在无色开环和闭环之间表现出可逆的光环化和开环反应。二芳基乙烯的光致变色活性和吸收最大值取决于芳基与乙烯部分的结合位置。当噻吩环在2位连接时，开环形式的吸收峰出现深色偏移，闭环形式的吸收峰出现次色偏移。这些趋势不仅在二亚乙烯中观察到，而且在二噻唑乙烯中也观察到。与合适的二（3-噻吩基）全氟环戊烯相比，二（2-噻吩基）全氟环戊烯具有优异的化学稳定性。噻吩环的α位比β位具有更高的电子密度。二乙烯的降解始于内过氧化物与噻吩环的反应。二（3-噻吩基）全氟环戊烯具有更多的反应性α -位，而二（2-噻吩基）全氟环戊烯的反应性α -位与强吸电子的全氟环戊烯相连，因此禁止氧化反应，并进行了二乙烯的化学稳定性研究。二乙烯分子有两个欧式构象。一种构象具有镜像对称（平行(p)取向）和另一种具有C2对称（反平行（a-p）取向）的芳香环。环化反应只从a-p构象进行。在双（1-苯并噻吩-3-基）全氟环戊烯苯并噻吩环的2′和2′位置引入异丙基，增加了a-p构象的居群，提高了环化反应的量子产率。

Diarylethenes show reversible photocyclization and ring-opening reactions between the colorless open-ring forms and the closed-ring forms.Photochromic reactivities and absorption maxima of diarylethenes were found to depend on the binding position of the aryl groups to the ethene moiety. When thiophene rings are connected at 2-position, the absorption maxima of the open-ring form showed bathochromic shifts, while the bands of closed-ring form showed hypsochromic shifts. These tendencies were observed not only in dithienylethenes but also in dithiazoylethenes.The di(2-thienyl)peffluorocyclopentenes showed excellent chemical stability compared with appropriate di(3-thienyl)perfluorocyclopentenes. The alpha-positions of thiophene ring has higher electron density compared with that of beta-positions. Degradation of dithienykethenes starts by the reaction of endoperoxide to the thiophene rings. Di(3-thienyl)perfluorocyclopentenes have more reactive alpha-positions, while in the di(2-thienyl)perfluorocyclopentenes reactive alpha-positions were connected with strong electron-withdrawing perfluocyclopentene ring, Therefore the oxidation reactions were prohibited, and chemical stabilitiy of the diarylethenes was performed.The diarylethene molecules have two atrope conformers. One conformer has two aromatic rings in mirror symmetry (in parallel (p) orientation) and the other in C2 symmetry (in antiparallel (a-p) orientation). The cyclization reaction proceeds only from the a-p conformer. Introduction of isopropyl groups to 2 and 2'-positions of benzothiophene rings of bis(1-benzothiophen-3-yl)perfluorocyclopentene increased the population of a-p conformer, and enhanced the quantum yield of the cyclization reaction.