Relations of the structures and the reactivities of Photochromic Diarylethenes.

二芳基乙烯的开环和开环反应是可逆的，其光致变色反应性和最大吸收值与乙烯基团与芳基的结合位置有关。当噻吩环在2位连接时，开环结构的吸收峰红移，而闭环结构的吸收峰红移。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。二噻吩基乙烯的降解开始于内过氧化物与噻吩环的反应。二（3-噻吩基）全氟环戊烯的α位反应活性较高，而二（2-噻吩基）全氟环戊烯的α位反应活性较强，与强吸电子的全氟环戊烯环相连，从而抑制了氧化反应，使二芳基乙烯具有化学稳定性。一种构象异构体具有镜像对称（平行（p）取向）的两个芳环，另一种构象异构体具有C2对称（反平行（a-p）取向）。环化反应仅从a-p构象异构体进行。在双（1-苯并噻吩-3-基）全氟环戊烯的苯并噻吩环的2位和2 '位引入异丙基，增加了α-β构象的布居数，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.