Electronic and vibrational structure in the S₀ and S₁ states of corannulene

Corannulene is a nonplanar aromatic hydrocarbon also known as a buckybowl. Its electronic and vibrational structure has been investigated by analyzing its fluorescence excitation spectrum and dispersed fluorescence spectrum in a supersonic jet. Its spectral features are in keeping with the expectation, confirmed by some previous results, that it has fivefold or C_5v symmetry. The observed prominent vibronic bands in the S₁ ← S₀ transition have been assigned to e₁ and e₂ bands on the basis of theoretical calculations so that the S₁ state was assigned to ¹E₂. The symmetry adapted cluster configuration interaction calculation supports this assignment of the S₁ electronic state, although the time-dependent density functional theory calculation suggests that the S₁ state is ¹A₂. It has also been shown that the normal coordinates for strong vibronic bands mainly include out-of-plane vibrational motion. The rotational envelopes are well explained by taking account of the Coriolis interaction between the degenerate vibrational and rotational levels. The mechanism of bowl-to-bowl inversion is also discussed with the results of theoretical calculations regarding the barrier to inversion and metastable conformation.