Extended Hückel Calculations on Azo and Azine Analogues of Polyacetylene
William B. Euler, Charles R. Hauer, Solid State Communications, 1984, 51, 473 – 476
Abstract
Extended Hückel calculations on the pi systems of polyazine, –(CH=N–N=CH)x–, and polyazoethene, –(CH=CH–N=N)x– are reported. Two methods were used to find polymer band properties: extrapolation to infinite length of a series of long chain molecules and by the tightbinding method using a basis set derived from monomer (four atom) molecular orbitals. For both polymers in the all trans configuration, four pi bands are found with the lower two filled and the upper two empty. The band gap in polyazoethene is found to be 0.4 to 0.7 eV, while the band gap in polyazine is 1.9 to 2.3 eV implying that polyazoethene is expected to be a substantially better semiconductor than polyazine. Analysis of the long chain wave functions shows that the bonding and antibonding functions of the dimers C=C and N=N for polyazoethene or C=N for polyazine are the appropriate orbitals to consider for describing the band properties of these polymers, and this the starting point for the tightbinding calculation.