TY - JOUR
T1 - Comparative theoretical study of the doping of conjugated polymers
T2 - Polarons in polyacetylene and polyparaphenylene
AU - Brédas, J. L.
AU - Chance, R. R.
AU - Silbey, R.
PY - 1982
Y1 - 1982
N2 - Defect-state calculations on all-trans polyacetylene and polyparaphenylene have been performed in the framework of the adiabatic Hückel Hamiltonian with σ-bond compressibility. In polyacetylene, the study of the energetics of the separation of the radical (neutral defect) -ion (charged defect) pair induced upon doping indicates that the two defects tend to remain in close proximity, resulting in the formation of a polaron. The binding energy of the polaron is estimated to be about 0.05 eV with this model. Absorption spectra at low doping levels are shown to be compatible with polaron formation, thus demonstrating the nonuniqueness of the previously proposed soliton model in explaining these absorption data. At higher doping levels, interaction between polarons leads to the formation of charged solitons carrying no spin. In polyparaphenylene, defects are always correlated in pairs due to the absence of a degenerate ground state. At low doping, polarons with a binding energy estimated at 0.03 eV are formed on ionization of polyparaphenylene. The related deformation of the lattice is relatively sof, in agreement with crystallographic data on biphenyl anions, and extends over about five rings. Increasing the doping level leads to the formation of bipolarons (doubly charged defects) that require a stronger deformation of the lattice and carry no spin. The possibility of a conduction mechanism in polyparaphenylene involving motion of bipolarons is consistent with magnetic data indicative of very low Pauli susceptibility in the metallic regime of SbF5-doped polyparaphenylene.
AB - Defect-state calculations on all-trans polyacetylene and polyparaphenylene have been performed in the framework of the adiabatic Hückel Hamiltonian with σ-bond compressibility. In polyacetylene, the study of the energetics of the separation of the radical (neutral defect) -ion (charged defect) pair induced upon doping indicates that the two defects tend to remain in close proximity, resulting in the formation of a polaron. The binding energy of the polaron is estimated to be about 0.05 eV with this model. Absorption spectra at low doping levels are shown to be compatible with polaron formation, thus demonstrating the nonuniqueness of the previously proposed soliton model in explaining these absorption data. At higher doping levels, interaction between polarons leads to the formation of charged solitons carrying no spin. In polyparaphenylene, defects are always correlated in pairs due to the absence of a degenerate ground state. At low doping, polarons with a binding energy estimated at 0.03 eV are formed on ionization of polyparaphenylene. The related deformation of the lattice is relatively sof, in agreement with crystallographic data on biphenyl anions, and extends over about five rings. Increasing the doping level leads to the formation of bipolarons (doubly charged defects) that require a stronger deformation of the lattice and carry no spin. The possibility of a conduction mechanism in polyparaphenylene involving motion of bipolarons is consistent with magnetic data indicative of very low Pauli susceptibility in the metallic regime of SbF5-doped polyparaphenylene.
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U2 - 10.1103/PhysRevB.26.5843
DO - 10.1103/PhysRevB.26.5843
M3 - Article
AN - SCOPUS:33749540003
SN - 0163-1829
VL - 26
SP - 5843
EP - 5854
JO - Physical Review B
JF - Physical Review B
IS - 10
ER -