The electron density isosurfaces of (a) the averaged twofold e 1-degenerate HOMO of neutral corannulene, (b) the HOMO of protonated corannulene, the SOMO of the cationic, (c) elongated (A′) structure, and (d) compressed (A″) structure.
FTIR KBr-pellet spectrum of neutral corannulene (top), and IRMPD spectra of corannulene+ (middle) and corannuleneH+ (bottom). Scaled harmonic B3LYP spectra are shown for neutral and protonated corannulene in green. The CC bond lengths of the pentagonal ring (X i ) shown in the corannulene structures adopt five different values for the protonated system (C1 symmetry), three different values for the radical cation (Cs symmetry) and all values are equivalent for neutral corannulene (C5v symmetry). Refer to text for further explanation.
The C5v molecular structure of neutral corannulene at the bottom shows the C5 symmetry axis and the five equivalent mirror plane elements (σv). The e 1 twofold degenerate HOMO is illustrated and the totally symmetric representation of the C5v point group is the ground electronic state of corannulene termed as 1A1. Upon ionization, the resulting 2E1-ground state of the open-shell corannulene cation is Jahn–Teller active and vibronic interaction (via E2 vibrational modes) lifts the degeneracy leading to two JT distorted Cs structures 2A′ and 2A″, corresponding to elongated and compressed molecular geometries of the corannulene radical cation, respectively. The geometric distortion due the JT effect is exaggerated for illustration.
IRMPD spectrum of corannulene+ compared to harmonic IR spectra calculated with the BP86, BLYP, B3LYP, and B3P86 DFT methods employing the cc-pVDZ basis set.
Comparison of the IRMPD spectra of corannulene and coronene radical cations.
Ground-state energies and structural parameters of corannulene (neutral and radical cation) calculated at several ab initio and DFT levels. For the cation, energy values in boldface indicate the lower of the two states. The columns “im” list the values for the imaginary frequency (first-order saddle point) or “0” for true minima.
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