The Role of the Intersection Space in the Photochemistry of Tricyclo[3.3.0.02,6]octa-3,7-diene

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• 作者：Luis Manuel Frutos ; Unai Sancho ; Marco Garavelli ; Massimo Olivucci ; Obis Casta&ntilde ; o
• 刊名：Journal of Physical Chemistry A
• 出版年：2007
• 出版时间：April 19, 2007
• 年：2007
• 卷：111
• 期：15
• 页码：2830 - 2838
• 全文大小：611K
• 年卷期：v.111,no.15(April 19, 2007)
• ISSN：1520-5215

文摘

CASSCF and CASPT2 methods were used to study the photochemistry of tricyclo[3.3.0.0^2,6]octa-3,7-diene(TOD). The analysis of different S₁ reaction paths as well as the topology of the S₁/S₀ intersection spaceallows us to establish two novel properties associated with the photochemical behavior of this compound: (i)simple low-lying intersection space domains can mediate different photoproducts, and (ii) TOD photochemistryis probably mediated by two disconnected intersection space domains, related to the formation ofcyclooctatetraene and semibulvalene in different time-scales. It is shown that these domains are chemicallydistinct since the first, leading to COT, mediates barrierless pericyclic reactions while the second, leading toSBV, is accessed through the formation of an excited-state biradical intermediate. To the best of our knowledge,in the domain of single molecule photochemistry, TOD represents the first example where a different chemicalrole of distinct low-lying intersection spaces has been computationally documented. The observed photoproductscan be rationalized in terms of branching space diagrams, constructed by determining the branching space(derivative coupling and gradient difference vectors) for each conical intersection involved in the photochemicalprocess.