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The X-band photoluminescence (PL) and PL-detected magnetic resonance (PLDMR) of C60- and C70-doped pristine 2,5-dihexoxy poly(p-phenylene vinylene) (DHOPPV), poly(3-dodecyl thiophene) (P3DT), and 2,5-dibutoxy poly(p-phenylene ethynylene) (DBOPPE) are described and discussed. While light (approximately 0.1 mol.%) doping of pristine DHOPPV sharply weakens the PL, it strongly enhances the PL-enhancing polaron and triplet exciton resonances, which are very weak in the undoped film. The polaron PLDMR is attributed to magnetic resonance enhancement of nonradiative trapped polaron pair recombination, which reduces the polaron population and consequently the rate at which they nonradiatively quench singlet excitons. Its behavior in 0.1 mol.% C60:DHOPPV is discussed in relation to the potential effects of C60-counterions, including the photogeneration of trapped polaron pairs at the expense of singlet excitons, and the fission of singlet excitons to such pairs. The emergence of the triplet resonance is discussed in relation to intersystem crossing from the singlet to the triplet manifold induced by the C60 dopant. At higher doping levels, the polaron and triplet exciton resonances weaken with increasing C60 content. The reduced polaron resonance is discussed in relation to the smaller relative change in the polaron population at the field for resonance, and the potential effects of the dissociation of the polaron pairs. The behavior of C70-doped pristine DHOPPV at up to 1 mol.% C70 is qualitatively similar to that of C60: DHOPPV, but the polaron resonance in P3DT and DBOPPE is less sensitive to C60. The triplet resonance is almost completely suppressed even in lightly doped P3DT and DBOPPE, which is attributed to quenching by the injected polarons.
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