Studies of photoexcited states in polyacetylene and poly(paraphenylenevinylene) by absorption detected magnetic resonance: The case of neutral photoexcitations

Photoexcited states in transpolyacetylene [t-(CH${)}_{\mathit{x}}$], and in alkoxy derivatives of poly(paraphenylenevinylene) (PPV) nondegenerate ground-state polymers, have been studied by the technique of absorption detected magnetic resonance. In addition to the stable charged photoexcitations, which are charged solitons in t-(CH${)}_{\mathit{x}}$ and bipolarons in PPV, we clearly identify neutral photoexcitations with nonzero spins. In t-(CH${)}_{\mathit{x}}$ these are spin-1/2 neutral solitons ${\mathit{S}}^0$(S¯ ${}_{}{}^0{}_{}{}^{}$) with an optical transition at 1.35 eV. The neutral photoexcitations in PPV form triplet excitons which cannot dissociate into ${\mathit{S}}^0$S¯ ${}_{}{}^0{}_{}{}^{}$ pairs due to the confinement caused by the nondegenerate backbone structure.