Theoretical Studies of Charged Defect States in Doped Polyacetylene and Polyparaphenylene

Defect statecalculations have been per formed for polyacetylene and polybparaphenylene in the fraamework of the Su, schriever, and Heeger Hamiltonian. In polyacetylene, the study of the energetics of the separation of the radical(natural defect)-ion(charged defect) pair induced upon doping indicates that the two defects tend to remain close to each other. This results in the formatn of polarons whose binding energy is estimated to be of the order of 0.05 eV Absorption spectra at low doping levels are consistent with polaron formation. Interaction between polarons leads to the formation of charged solitions. In poly(p-phenylene), defects are always correlated in pairs. Upn doping, polarons are formed (binding energy ∼ 0.03 eV), wit the relaxation of the lattice extending over about four rings. Calculations suggest the possibility of bipolarons (doubly charged defects) that yield conductivity without Pauli susceptibility.