Electronic structures of carbyne model compounds

Photoelectron spectra of compounds having carbyne skeletal structures have been measured. The photoelectron spectra of the compounds having a cumulene type carbon bonds (=C=C=C=C=) reveals that the highest occupied molecular orbital (HOMO) level becomes shallower in accordance with the increase of the carbon chain length. The spectra of two compounds having –C≡C–C≡C– bond were reproduced well by MO calculation, which allows us to estimate the electronic structure of much longer carbon chain. The calculation indicates the same carbon chain length dependence in polyyne type compounds as are observed in cumulene type compounds.