The low-lying excited states of 1,6-methano[10] annulene

The electronic absorption spectrum of 1,6-methano[10] annulene in the region of the S-0-->S-1 and S-0-->S-2 transitions was investigated at room and low temperature. By comparison with the one-photon spectrum of naphthalene, and considering pseudoparity selection rules, the strong 33 000 cm(-1) band of the annulene derivative is assigned as the inductively perturbed S-0-->S-2 (L-a(+)) electronic transition. The rich vibronic structure of the S-0-->S-1 transition at low temperature is discussed in terms of Franck-Condon allowed transitions. The calculated intensities of the fundamental modes are in qualitative agreement with the experimental data. (C) 1997 Elsevier Science S.A.