The origin of excitations in multi-chromophore carbon network substructures based on dodecadehydrotribenzo[18]annulene has been investigated by steady-state and photon echo spectroscopy, configuration interaction (CIS and CIS(D)), and time-dependent density functional theory (TD-DFT). 1,4-diphenylbutadiyne, the simplest structural subunit within the annulene, was used in modeling the spectroscopic studies to explain the origin of excitations in the macrocycles. The optical excitations in longer linear systems were found to be similar to its diphenylacetylene analogue. However, the results from dodecadehydrotribenzo[18]annulene and other multichromophore networks systems illustrate the possibility of strong intramolecular interactions and the formation of delocalized excited states. Calculations were carried out to explain the basic similarities and differences in excitations of the model compounds such as diphenylbutadiyne and the macrocycles. The fundamental excitation in these systems can be primarily described as a pi --> pi* transition. Two low-energy resonances were observed from experiment for the annulene systems, and possible explanations for these low-energy resonances in the macrocycles are explored. The significant difference found in the calculated oscillator strength of the two low-energy bands for the macrocycles as well as the dynamics of solvent interactions was further investigated by three-pulse photon echo measurements. A simple exciton model was developed to discuss the excitations in the larger macrocycles. The results from this model were found to be in good agreement with the TD-DFT calculations.

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The singlet potential energy surface for the dissociation of benzene dication has been explored, and its three major dissociation channels have been studied: C6H6(2+) --> C3H3(+) + C3H3(+), C4H3(+) + C2H3(+), and C5H3(+) + CH3(+). The calculated energetics suggest that the products will be formed with considerable translational energy because of the Coulomb repulsion between the charged fragments. The calculated energy release in the three channels shows a qualitative agreement with the experimentally observed kinetic energy release. The formation of certain intermediates is found to be common to the three dissociation channels.