Second moments of ESR signals from poly(p‐phenylene) and the deuterated analog

The second moments of the ESR signals obtained from poly(p‐phenylene) (PPP) and deuterated PPP were measured at 9.5 and 35 GHz. The theoretical and experimental contributions to the second moments were considered. It is shown that for deuterated PPP, deuteron hyperfine splitting makes a negligible contribution to the observed second moment. The proton hyperfine contributions to the second moments of the radical species in PPP and p‐sexiphenyl were estimated and it was concluded that the unpaired electron was delocalized over only 2‐4 phenylene units. A rationale is offered in terms of polarons present as defects in the PPP chains.