ESEEM study on a stable paramagnetic center in polydiacetylene having a π-conjugated ladder structure

Using two-, three- and five-pulse methods, we have measured the electron spin echo envelope modulation (ESEEM) of a stable paramagnetic center existing in a non-doped ladder polymer, in which two polydiacetylenes are conjugated in each repeating unit. A relatively deep modulation effect owing to weak hyperfine interaction with protons was observed. The number of interacting protons was estimated to be a few tens based on the analysis of the modulation amplitude. The interaction with many protons implies that the paramagnetic center in the ladder polydiacetylene also possesses a wavefunction delocalized on several units in the π-conjugated system like the spin solitons in polyacetylene.