Structure and energy spectra of a class of polybenzenoid Clar's hydrocarbons and 1-D polymers

The energy spectra of a class of 2-D polybenzenoid Clar's hydrocarbons with a large number N(N similar to 10(4)) of carbon atoms is studied theoretica lly. It is shown that at the asymptotic case N-->infinity the energy gap (E G) Delta E (N --> infinity) is different from zero, i.e., the pi-systems sh ould possess semiconductor properties. The results for the EG Delta E (N -- > infinity) not equal 0 of the hydrocarbons are in qualitative agreement wi th the results for the EG calculated for a class of 1-D ladder polymers hav ing the same edge structure as the hydrocarbons. With increasing the number (M) of the pi-centers of the elementary unit of the polymers, the band gap Delta E(M-->infinity) approaches also to a value different from zero. The quantitative results on the equlibria geometries of the hydrocarbons and th e polymers correspond to Clar's qualitative characterization of benzenoids composed of disjoint "pi-sextets". The energetics of the hydrocarbons with different types of defects and the corresponding Tamm and Frenkel states we re also investigated.