Polarons and triplet polaronic excitons in poly(paraphenylenevinylene) (PPV) and substituted PPV: An optically detected magnetic resonance study

Abstract

The X-band optically detected magnetic resonance (ODMR) of poly(paraphenylenevinylene) (PPV) and its dihexoxy derivative films and solutions is described and discussed. As in poly(3-alkylthiophenes) (P3AT), the photoluminescence (PL) -enhancing features include a narrow resonance at g≃2.0023, a broad triplet powder pattern around g∼2, and the Δ${\mathit{m}}_{\mathit{S}}$=2 transition of this triplet at g≃4.07. The symmetric narrow resonance, attributed to intrachain ‘‘distant’’ polaron recombination, indicates that charge-conjugation symmetry violation is weaker in PPV than in P3AT. As in P3AT, its spectral dependence is similar to the PL spectrum, suggesting that the polaron levels are close to the band edges. Although the spectral dependence of the half-field resonance is similar, that may result from singlets generated by triplet-triplet collisions. A broad decrease in the ODMR intensity at g∼2, probably due to a PL-quenching resonance resulting from geminate singlet decay, is also observed at low temperatures.