BAND-STRUCTURE OF QUASI-ONE-DIMENSIONAL POLYCONDENSED AROMATIC-HYDROCARBONS .1. POLY(PERIACENE)S

The energy spectrum of a group of poly(periacene)s (PPAcs) is investigated theoretically. The topological (DELTA(top)), geometrical (DELTA(geom)) and correlation (DELTA(corr)) contributions to the energy gap DELTA-E(infinity) are examined, with DELTA-E(infinity) = [DELTA(corr)2 + (DELTA-(top) + DELTA(geom))2]1/2. If the number of benzene rings n within the elementary unit reaches infinity (n --> infinity), the bandgap vanishes, but the DELTA-E(infinity)(n) values do not decrease in a monotonic fashion. It appears that PPAc can be classified into the following two series: the (3n + 2) and the (3n + p) series with p = 1, 3; in each series DELTA-E(infinity) decreases monotonically. The frontier MOs of the two series, which determine the energy gap, belong to different irreducible representations of the symmetry group D(2m)h. The MOs of the (3n + 2) series are symmetric with respect to reflection in the mirror plane sigma(h), while the MOs of the (3n + p) series are asymmetric. The connection between the symmetry of the frontier MOs and the energy spectrum of the PPAcs is discussed.