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 (EG) Delta E (N --> infinity) is different from zero, i.e., the pi-systems should possess semiconductor properties. The results for the EG Delta E(N - -> infinity) not equal 0 of the hydrocarbons are in qualitative agreement w ith the results for the :EG calculated for a class of I-D ladder polymers h aving the same edge structure as the hydrocarbons. With increasing the numb er (M) of the pi-centers of the elementary unit of the polymers, the band g ap Delta E(M --> infinity) approaches also to a value different from zero. The quantitative results on the equlibria geometries of the hydrocarbons an d the polymers correspond to Clar's qualitative characterization of benzeno ids composed of disjoint "pi-sextets". The energetics of the hydrocarbons w ith different types of defects and the corresponding Tamm and Frenkel state s were also investigated.