Theoretical analysis of conjugated polymers with a degenerate ground state: Type-I and type-II soliton charge storage states in poly(1,6-heptadiyne) and derivatives

We report a theoretical study of the molecular and electronic structure of polymers with a degenerate ground state based on poly(1,6-heptadiyne). Quantum-chemical calculations are performed by means of the semiempirical Austin Model 1 and intermediate neglect of differential overlap/configuration interaction methods as well as the nonempirical valence effective Hamiltonian technique. In the case of poly(1,6-heptadiyne) itself and poly(dipropargyl- hexylamine), we first examine the torsion potential along the backbone; we then investigate the doping-induced electronic and geometric modifications. We also consider the self-doped n-type system, poly(dipropargylhexylmethylammonium). The charge-storage states induced upon doping are discussed in terms of the formation of solitons, which belong to two different types and have characteristics at variance with respect to those in trans-polyacetylene.