Triplet exciton reactions in MEH-PPV films registered by accompanying magneto-sensitive photoluminescence

[Display omitted] •The magnetic field effect on MEH-PPV photoluminescence can be inverted by varying molecular oxygen concentrations.•The theoretical model based on kinetic-balance equations allows describing the effects.•The model includes the magnetic-field-insensitive T-1Δg(O2) cross-annihilation process.•Triplet-triplet annihilation of excitons and quenching of triplet excitons by molecular oxygen are necessary to explain the effects. Magneto-sensitive delayed photoluminescence (DPL) of the deaerated MEH-PPV films in the presence of an external magnetic field is investigated. The obtained results have shown that the sign of the magnetic field effect on DPL can be inverted by varying molecular oxygen concentration in the films. For explaining the “sign-inversion” of the magnetic field effect on DPL, the mathematical model based on the superposition of exciton-initiated reactions was proposed. The magnetic field dependencies of DPL based on the theoretical model were calculated. The calculations of the magnetic field effects on DPL confirm the “sign-inversion effect”. Also, the critical molecular oxygen concentration when the magnetic field effect on DPL disappears was determined theoretically. The obtained results can be used for the detection of spin-selective exciton-initiated reactions as well as for the determination of molecular oxygen concentration in MEH-PPV films.