Investigation and comparison of the electro-photo property of carbon-rich chain and cycle compounds

We investigate the electron-photo property of molecular macrochain and macrocycle compounds, which are constructed with phenylene and acetylene. Their electronic transition spectra and the second hyperpolarizability coefficients are calculated using ab initio and semiempirical methods. The energy gaps for the chain and ring molecules are shown to have very different regularity. The electronic transition wavelengths for chain and ring compounds are estimated to be shorter than 400 nm. The average values of the second-order hyperpolarizability coefficients per molecular unit increase with increasing number of the units. The asymptotic values are extrapolated to be 5.15 and 3.93×105 a.u. for chain and cycle compounds, respectively. These results show that they can be a kind of promising third order NLO material with high hyperpolarizability as well as good transparency to visible light.