Relations of the structures and the reactivities of Photochromic Diarylethenes.

二芳基乙烯在无色开环形式和闭环形式之间表现出可逆光环化和开环反应，其光致变色反应活性和吸收峰取决于芳基与乙烯基团的结合位置。当噻吩环连接在2位时，开环形式的吸收峰发生深色位移，而闭环形式的吸收峰出现次色位移。这些趋势不仅存在于二硫杂环戊烯中，而且还存在于二硫杂环戊烯中。与适当的二(3-硫杂环戊烯)全氟环戊烯相比，二(2-噻吩基)全氟环戊烯具有良好的化学稳定性。与β位相比，噻吩环的α位具有更高的电子密度。二硫杂环己烯的降解始于内过氧物与噻吩环的反应。二(3-噻吩基)全氟环戊烯具有更多的活性α位，而二(2-噻吩基)全氟环戊烯的活性α位与强吸电子的全氟环戊烯环相连，从而抑制了氧化反应，提高了二芳基乙烯的化学稳定性。一个构象有两个镜像对称的芳环(平行(P)取向)，另一个具有C2对称(反平行(a-p)取向)。环化反应仅从a-p构象开始。在bis(1-benzothiophen-3-yl)perfluorocyclopentene的苯并噻吩环的2和2‘-位引入异丙基，增加了a-p构象的布居，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.