Comment on "Frequency response and origin of the spin-1/2 photoluminescence-detected magnetic resonance in a π-conjugated polymer

In a recent paper, Segal [Phys. Rev. B 71, 245201 (2005)] advanced a new explanation for the dynamics of spin-(1)(2) photoluminescence-detected magnetic resonance (PLDMR) in films of a pi-conjugated polymer, namely, a soluble derivative of poly(phenylene-vinylene) (MEH-PPV), using a model [dubbed triplet-polaron quenching (TPQ)], in which the PLDMR is due to spin-dependent triplet-polaron interactions that reduce the polaron density and consequent quenching of singlet excitons. We studied a fuller PLDMR and photoinduced absorption (PA) and photoinduced absorption detected magnetic resonance (PADMR) dynamics (both frequency and time resolved) of MEH-PPV films as a function of microwave power at various temperatures. We show that (i) the TPQ model in the work of Segal et al. is incompatible with the extended frequency dependent spin-(1)(2) PLDMR response; (ii) the spin-(1)(2) PADMR and PLDMR dynamics are not the same, in contrast to the TPQ model; (iii) the TPQ model is not in agreement with the spin-1 PLDMR temperature dependence in relation to that of the spin-(1)(2) PLDMR; and (iv) the TPQ model predicts a much shorter triplet exciton lifetime than that obtained experimentally via PA. In contrast, the alternative model advanced previously [Z. V. Vardeny and X. Wei, in Handbook of Conducting Polymers, 2nd ed., edited by T. A. Skotheim, R. L. Elsenbaumer, and J. R. Reynolds (Dekker, New York, 1998), pp. 639-666], namely, the spin-dependent recombination of polarons, is capable of explaining the whole body of experimental results and, in particular, the spin-(1)(2) PLDMR and PADMR dynamics.