EPR study of polarons in a conducting polymer with nondegenerate ground states: Alkali metal complexes of poly (p-phenylene) and phenylene oligomers

Journal Article · Wed Aug 15 04:00:00 EDT 1984 · J. Chem. Phys.; (United States)

DOI:https://doi.org/10.1063/1.447836· OSTI ID:7056613

Kispert, L D; Joseph, J; Miller, G G; Baughman, R H

EPR measurements are used to characterize electronic states relevant for carrier transport in alkali metal doped poly(p-phenylene), PPP, fully deuterated poly(p-phenylene), DPPP, and phenylene oligomers. Observed spin concentrations per carbon are at least one decade higher than the Curie spin concentration for Na-doped polyacetylene. The number of these spins, which likely corresponds to polarons (mobile radical anions), is much less than the amount of alkali metal dopant, suggesting that much of the charge on the polymer chains is in bipolarons (spinless dianions). Relevant to the interaction between spins on the polymer chain and the metal cations, the observed g values are close to the free electron value and do not substantially vary with the donor dopant, temperature, or the molecular weight of the phenylene chain. Although the spin-orbit effect on g values is small, room temperature linewidth tends to increase with increasing atomic number of dopant: suggesting some interaction, albeit a smaller magnitude effect than for alkali-metal graphite complexes. The EPR linewidths are exchange narrowed and proton hyperfine broadening is significant. The latter explains the generally broader linewidths for doped PPP than for doped DPPP. The measured susceptibilities have a temperature dependence which suggests equilibrium between separated polaron defects and singlet and triplet spin states formed intermolecularly via polaron pairing. The interaction is antiferromagnetic and the binding energy between polarons is about 2.2 to 3.3 meV. An upper limit estimate of the Fermi-surface density of states for K-doped PPP (0.7 states/eV phenyl) is derived from an upper limit estimate of Pauli susceptibility.

• Research Organization: Department of Chemistry, University of Alabama, Tuscaloosa, Alabama 35486
• OSTI ID: 7056613
• Journal Information: J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 81:4; ISSN JCPSA
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360404* -- Materials-- Polymers & Plastics-- Physical Properties-- (-1987)
ALKALI METAL COMPLEXES
ANGULAR MOMENTUM
COMPLEXES
DOPED MATERIALS
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
ELECTRON SPIN RESONANCE
ELECTRONIC STRUCTURE
LINE BROADENING
LINE WIDTHS
MAGNETIC RESONANCE
MATERIALS
ORGANIC COMPOUNDS
ORGANIC POLYMERS
PARTICLE PROPERTIES
PHENYLENE RADICALS
PHYSICAL PROPERTIES
POLARONS
POLYMERS
QUASI PARTICLES
RADICALS
RESONANCE
SPIN
TEMPERATURE DEPENDENCE