Quantum chemical characterization of low-energy states of calicene in the gas phase and in solution

Giovanni Ghigo, Abdul Rehaman Moughal Shahi, Laura Gagliardi, Lee M. Solstad, Christopher J. Cramer

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13 Scopus citations


(Figure Presented) The ground and excited electronic state properties of calicene (triapentafulvalene or 5-(cycloprop-2-enl-ylidene)cyclopenta-1,3-diene) have been studied with a variety of density functional models (mPWPW91, PBE, TPSS, TPSh, B3LYP) and post-Hartree-Fock models based on single (MP2 and CCSD(T)) and multideterminantal (CASPT2) reference wave functions. All methods agree well on the properties of ground-state calicene, which is described as a conjugated double bond system with substantial zwitterionic character deriving from a charge-separated mesomer in which the three- and five-membered rings are both aromatic. Although the two rings are joined by a formal double bond, contributions from the aromatic mesomer reduce its bond order substantially. A rotational barrier of 40-41 kcal mol-1 is predicted in the gas phase and solvation effects reduce the barrier to 37 and 33 kcal mol-1 in benzene and water, respectively, because of increased zwitterionic character in the twisted transition-state structure. Multi-state CASPT2 (MS-CASPT2) is used to characterize the first few excited singlet and triplet states and indicates that the most important transition occurs at 4.93 eV (251 nm). A cis-trans photoisomerization about the inter-ring double bond is found to be inefficient.

Original languageEnglish (US)
Pages (from-to)2823-2831
Number of pages9
JournalJournal of Organic Chemistry
Issue number8
StatePublished - Apr 13 2007


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