Coherent and incoherent spin-relaxation dynamics of electron-hole pairs in a π -conjugated polymer at low magnetic fields

We report room-temperature measurements of the spin-relaxation times T₁ and T₂ of electron-hole charge-carrier spins in an organic light-emitting diode based on the π-conjugated polymer SY-PPV at low (10.16em0exmTB₀100.16em0exmT) static magnetic fields, using electrically detected---through spin-Rabi oscillation-controlled recombination currents---magnetic resonant Hahn-echo and inversion-recovery pulse sequences. When random local hyperfine fields and external magnetic fields compete in magnitude, charge carrier spin-quantization axes are no longer well defined, and striking magnetic-field dependencies of spin-lattice relaxation times are found, while spin coherence times remain mostly field-independent. These results corroborate the magnetic-field sensitivities of observables governed by radical-pair physics.