Pressure Catalyzed Bond Dissociation in an Anthracene Cyclophane Photodimer

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• 作者：Sebastian R. Jezowski ; Lingyan Zhu ; Yaobing Wang ; Andrew P. Rice ; Gary W. Scott ; Christopher J. Bardeen ; Eric L. Chronister
• 刊名：The Journal of the American Chemical Society
• 出版年：2012
• 出版时间：May 2, 2012
• 年：2012
• 卷：134
• 期：17
• 页码：7459-7466
• 全文大小：343K
• 年卷期：v.134,no.17(May 2, 2012)
• ISSN：1520-5126

文摘

The anthracene cyclophane bis-anthracene (BA) can undergo a [4 + 4] photocycloaddition reaction that results in a photodimer with two cyclobutane rings. We find that the subsequent dissociation of the dimer, which involves the rupture of two carbon鈥揷arbon bonds, is strongly accelerated by the application of mild pressures. The reaction kinetics of the dimer dissociation in a Zeonex (polycycloolefin) polymer matrix were measured at various pressures and temperatures. Biexponential reaction kinetics were observed for all pressures, consistent with the presence of two different isomers of bis(anthracene). One of the rates showed a strong dependence on pressure, yielding a negative activation volume for the dissociation reaction of 螖V = 鈭?6 脜³. The 93 kJ/mol activation energy for the dissociation reaction at ambient pressure is lowered by more than an order of magnitude from 93 to 7 kJ/mol with the application of modest pressure (0.9 GPa). Both observations are consistent with a transition state that is stabilized at higher pressures, and a mechanism for this is proposed in terms of a two-step process where a flattening of the anthracene rings precedes rupture of the cyclobutane rings. The ability to catalyze covalent bond breakage in isolated small molecules using compressive forces may present opportunities for the development of materials that can be activated by acoustic shock or stress.