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The endohedral fullerene CH4@C84 has been studied using density functional theory (DFT) and second-order Møller-Plesset perturbation theory (MP2). In addition to the structure with a C— bond of CH4 in a tetrahedral pocket conformation, we find an alternative minimum, very close in energy (6.3-9.5 kJ/mol higher according to the level of theory), with the methane inverted, which we call the antipocket conformation. Computed IR spectra are reported for CH4@C84 and also for the reference system CH4@C60. The calculated vibrational levels, in a harmonic approximation, reveal close-lying translational, librational, and shell-vibrational modes. The results are also presented for the isoelectronic species NH4+@C60. |
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A series of 6-styryl-2,4-diphenylpyrylium salts exhibiting dual fluorescence has been investigated by fluorescence up-conversion in conjunction with quantum chemical calculations. The short-wavelength emission is due to an excited state localized on the pyrylium fragment and the long-wavelength emission arises from a charge-transfer state delocalized over the whole molecule. The two fluorescing states do not exhibit a precursor−successor relationship. The rise time of the short-wavelength fluorescence is smaller than 200 fs, and that of the long-wavelength emission depends on the electron-donating property of the styryl group substituent. The rise is almost prompt with the weaker donors but is slower, wavelength and viscosity dependent with the strongest electron-donating group. A model involving a S2/S1 conical intersection is proposed to account for these observations. |