TY - JOUR
T1 - Quantum chemical characterization of low-energy states of calicene in the gas phase and in solution
AU - Ghigo, Giovanni
AU - Shahi, Abdul Rehaman Moughal
AU - Gagliardi, Laura
AU - Solstad, Lee M.
AU - Cramer, Christopher J.
PY - 2007/4/13
Y1 - 2007/4/13
N2 - (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.
AB - (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.
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U2 - 10.1021/jo062420y
DO - 10.1021/jo062420y
M3 - Article
C2 - 17371070
AN - SCOPUS:34247353814
VL - 72
SP - 2823
EP - 2831
JO - Journal of Organic Chemistry
JF - Journal of Organic Chemistry
SN - 0022-3263
IS - 8
ER -