Excited states of 1,6-methano[10]annulene: site selection fluorescence and fluorescence excitation spectroscopy on S1.

Fluorescence, S1-f S0, and fluorescence excitation, S0 - S1, spectra of 1,6-methano[10]annulene have been measured in glassy matrixes at low temperature under moderate site selection conditions. The polarization ratios of both spectra have been also measured at 77 K. MO ab initio calculations including correlation effects indicate that the molecule has one energy minimum in the ground state and one in the lowest excited singlet state. They correspond to bond-equalized structures of aromatic character. The spectra are accordingly discussed in terms of transitions involving the aromatic form of 1,6-methano[10]annulene. A good correlation is found between observed and calculated Franck-Condon intensities.