Cyclooctatetraene computational photo- and thermal chemistry: A reactivity model for conjugated hydrocarbons

Marco Garavelli, Fernando Bernardi, Alessandro Cembran, Obis Castaño, Luis Manuel Frutos, Manuela Merchán, Massimo Olivucci

Research output: Contribution to journalArticle

56 Scopus citations

Abstract

We use ab initio CASSCF and CASPT2 computations to construct the composite multistate relaxation path relevant to cycloocta-1,3,5,7-tetraene singlet photochemistry. The results show that an efficient population of the dark excited state (S 1) takes place after ultrafast decay from the spectroscopic excited state (S 2). A planar D 8h-symmetric minimum represents the collecting point on S 1. Nonadiabatic transitions to S 0 appear to be controlled by two different tetraradical-type conical intersections, which are directly accessible from the S 1 minimum following specific excited-state reaction paths. The higher-energy conical intersection belongs to the same type of intersections previously documented in linear and cyclic conjugated hydrocarbons and features a triangular -(CH) 3- kink. This point mediates both cis → trans photoisomerization and cyclopropanation reactions. The lowest energy conical intersection has a boat-shaped structure. This intersection accounts for production of semibullvalene or for double-bond shifting. The mapping of both photochemical and thermal reaction paths (including also Cope rearrangements, valence isomerizations, ring inversions, and double-bond shifting) has allowed us to draw a comprehensive reactivity scheme for cyclooctatetraene, which rationalizes the experimental observations and documents the complex network of photochemical and thermal reaction path interconnections. The factors controlling the selection and accessibility of a number of conjugated hydrocarbon prototype conical intersections and ground-state relaxation channels are discussed.

Original languageEnglish (US)
Pages (from-to)13770-13789
Number of pages20
JournalJournal of the American Chemical Society
Volume124
Issue number46
DOIs
StatePublished - Nov 20 2002

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