Electronic structure of poly(iminomethylene) using semi-empirical methods

• Published in: Journal of molecular structure. Theochem 2002-02, Vol.578 (1), p.1-17
• Main Authors: Young, Vaneica Y, Hellmuth, Eckard W
• Format: Article
• Language: English
• Subjects: AM1; Electronic structure; PM3; Poly(iminomethylene)
• ISSN: 0166-1280; 1872-7999
• DOI: 10.1016/S0166-1280(01)00679-0

The electronic structure of poly(iminomethylene), the parent polymer for a class of rigid rod polymers known as polyisocyanides, has been studied by semi-empirical methods using the AM1 and PM3 hamiltonians. All of the possible helical geometries, 2 1, 3 1 and 4 1, as well as pseudo-helical and more generalized geometries have been studied. The most stable geometry is a generalized structure with four residues per translational unit, which is only slightly distorted from a helical geometry. It is an isotactic geometry, with the hydrogen substituents directed parallel to the screw direction. The most stable helical geometry has three residues per translational unit. The C–C bond lengths for the 2 1 geometries are longer than those for the 3 1 and 4 1 geometries, but the calculated band gaps are smaller for the former. The calculated density of states for the 3 1 and 4 1 geometries are not highly correlated. For a set of polyisocyanides with the same conformation, the density of states of the parent polymer is expected to be a good approximation to the backbone density of states of the members of the set.