Catenane and inclusion complex as photochromic compounds involving viologen units

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• 作者：Tetsuo Kuwabara ; Maki Sugiyama ; Kazutoshi Takeuchi ; Hideto Sakane
• 关键词：Photochromism ; Catenane ; Viologen ; Crown ether ; Inclusion ; Supramolecule
• 刊名：Journal of Photochemistry and Photobiology A: Chemistry
• 出版年：2013
• 出版时间：1 October, 2013
• 年：2013
• 卷：269
• 期：Complete
• 页码：59-64
• 全文大小：624 K

文摘

Catenane (1) consisting of a tetracationic cyclophane (2) and p-benzocrown ether (5) has been prepared to investigate its photochromic behavior in a poly(N-vinyl-2-pyrroridone) (PVP) film by comparing with that of 2 in the absence and the presence of ¦Ð-electron donating guests such as indole (6) and p-dimethoxybenzene (7). The PVP film containing 1 showed a red color due to the ¦Ð-donor/¦Ð-acceptor charge transfer interaction between the viologen and the dialkoxybenezene units in 1. Upon photoirradiation the film changed the color to blue with the absorption maximum (¦Ë_max) at 620 nm, associated with the photoreduction of the viologen unit from the dication to the radical cation, and reverted to the original dication with the half-life (¦Ó_1/2) of 15 min. The pale yellow film containing 2 showed the similar photochromic behavior to that of 1 with ¦Ë_max at 610 nm and ¦Ó_1/2 at 24 min, which are shifted to blue side by 10 nm and to longer time by 9 min as compared with those of 1. The difference in the photochromic behavior between 1 and 2 is resulted from the existence of the ¦Ð-electron donating unit, 5, which is interlocked with the ring of 2 in the compound 1. The effect of the ¦Ð-electron donating unit on the photochromic behavior of viologen was confirmed by the addition of 6 and 7 to the film containing 2 or its acyclic analog, 3. The ¦Ë_max and ¦Ó_1/2 for the photoreduced 2 were observed at 620 nm and 14 min, and at 615 nm and 20 min in the presence of 6 and 7, respectively. The larger effect of 6 rather than 7 on the photochromic properties of 2 was interpreted in terms of the larger binding constant of 6 with 2 than that of 7 in dimethylacetamide (DMAc) (3.0 and 2.3 M^?1 for 6 and 7, respectively). The addition of 6 and 7 to the film containing 3 caused no change in the photochromic properties of 3 (¦Ë_max = 611 nm and ¦Ó_1/2 = 22 min). When the simple benzylviologen (4) was used as the photochromic compound, the reversion rate of the photoreduced 4 was accelerated by the addition of 5 but it was not accelerated by 7. All these results demonstrate that the cyclic structure as well as the catenane promote the strong interaction between viologen and ¦Ð-electron donating units. The interaction leads the change not only in color of the film before photoirradiation but also in the photochromic behaviors of viologen derivatives.