Light-Induced EPR study of spin-assisted charge transfer in PANI-ES/P3DDT/PCBM composite

The first results of the Light-Induced EPR (LEPR) study of magnetic, relaxation and dynamic parameters of charge carriers stabilized in emeraldine salt form of polyaniline (PANI-ES) highly doped with sulfuric (SA) and para-toluenesulfonic (pTSA) acids, spin pairs photoinitiated in bulk heterojunctions formed by poly(3-dodecylthiophene) with [6,6]-phenyl-C₆₁-butyric acid methyl ester (P3DDT/PCBM) as well as in appropriate PANI-ES/P3DDT/PCBM composites are described. Magnetic resonance parameters of polarons and methanofullerene ion radicals photoinitiated in bulk heterojunctions were determined separately from their deconvoluted LEPR spectra to be governed by the conformation of the PANI network. Initial PANI-ES samples exhibit single EPR spectra of polarons P₁ with temperature independent g-factor equal to 2.0031 for PANI-SA and 2.0028 for PANI-pTSA, whereas spin pairs P₂-mC₆₁ photoinitiated in the P3DDT/PCBM bulk heterojunctions are characterized by double LEPR spectrum contributed by these charge carriers with isotropic g-factors equal to 2.0018 and 1.9997, respectively. Both the effective spin relaxation and susceptibility were described in terms of the exchange interaction of the polarons hopping in the neighboring solitary PANI and P3DDT matrices. Such interaction increases dramatically as the PANI-SA network is replaced by the PANI-pTSA one in the triple composite due to the deeper overlapping of wave functions of polarons in both polymer matrices and the rising of the energy barrier which they overcome crossing appropriate bulk heterojunctions. Polaron P₂ diffusion in P3DDT was shown to govern spin susceptibility of mC₆₁ rotating between its chains. We have first showed an ability to control/handling the texture, structural and electronic properties of these composites by the method used for further creation under controllable synthesis of various flexible and scalable organic molecular devices with optimal coherent-spin-assisted electronic properties. A strategy to create relevant spintronic devices using the other ingredients of the composite is discussed.