Structure and Energy Spectra of a Class of Polybenzenoid Clar's Hydrocarbons and 1-D Polymers

Abstract

The energy spectra of a class of 2-D polybenzenoid Clar 's hydrocarbons with a large number N(N∼104) of carbon atoms is studied theoretically. It is shown that at the asymptotic case N → ∞ the energy gap (EG) ΔE (N → ∞) is different from zero, i.e., the π-systems should possess semiconductor properties. The results for the EG ΔE (N → ∞) ≠ 0 of the hydrocarbons are in qualitative agreement with the results for the EG calculated for a class of 1-D ladder polymers having the same edge structure as the hydrocarbons. With increasing the number (M) of the π-centers of the elementary unit of the polymers, the band gap ΔE(M → ∞) approaches also to a value different from zero. The quantitative results on the equilibria geometries of the hydrocarbons and the polymers correspond to Clar 's qualitative characterization of benzenoids composed of disjoint “π-sextets”. The energetics of the hydrocarbons with different types of defects and the corresponding Tamm and Frenkel states were also investigated.