Electronic structures of cumulene type carbyne model compounds: a typical example of one-dimensional quantum well

Ultraviolet photoelectron spectra of linear chain cumulene type carbyne model compounds with phenyl terminal groups to stabilize the chain have been measured and assigned with semi-empirical molecular orbital (MO) calculation. The spectra can be basically divided into two parts; contributions from phenyl groups and the chain part. The longer the chain length becomes, the lower the binding energy of the highest occupied molecular orbital (HOMO). The MO calculation reveals that the HOMO of these compounds derives from the carbon chain part and supports experimental results on chain length dependence of the HOMO. The HOMO and the lowest unoccupied molecular orbital (LUMO) of the model compounds are considered in terms of one-dimensional quantum well.