Nonradiative quenching of singlet excitons by polarons in π-conjugated polymers

The photoluminescence (PL)-detected magnetic resonance (PLDMR) of various pi -conjugated materials, including poly(p-phenylene vinylenes) (PPVs), isolated PPV chains in a nano-structured liquid crystal host, methyl-substituted ladder-type poly(p-phenylene), and oligophenylenes are described. All of the results are in excellent quantitative agreement with a rate-equation model in which the positive (PL-enhancing) spin 1/2 PLDMR is due to the role of polarons in nonradiative quenching of singlet excitons. The results also suggest that this quenching process is very significant in luminescent pi -conjugated materials and organic light-emitting devices, and should be taken into account, especially at high excitation densities such as in lasing action.