Different conjugated molecular systems are electronically characterized by means of continuous-wave and pulsed electron paramagnetic resonance as the main spectroscopic technique, complemented with other techniques, i.e. photoinduced absorption, steady-state UV-Vis absorption and density functional theory computations. The studied systems are fullerene derivatives with radical(s) as ligand, perfluoroalkyl perfluorinated phthalocyanines and methoxy-3,7-dimethyl-octoxy-poly(phenylene vinylene) (MDMO-PPV)-based devices.

The fullerene derivatives consist of a C₆₀ buckminsterfullerene to which one or more stable nitroxide radicals are attached. They have been characterized at 95 GHz with the emphasis on the electronic (exchange) interaction between the photoexcited fullerene moiety and the attached radical(s). High-field experiments revealed magnetic sublevels of the system which could not be observed before. Earlier proposed mechanisms for the time evolution of the spin polarization, i.e. the spin dynamics, have to be reconsidered in view of the obtained results. The sign of the exchange coupling, i.e. ferromagnetic or anti-ferromagnetic coupling, is probably mediated by super-exchange coupling mechanisms through the linker connecting the radical and the fullerene unit.

The studied phthalocyanine compounds (F₆₄PcM) are highly fluorinated phthalocyanines with bulky sidegroups and different metals (M = Cu(II), Co(II), VO(II), or Zn(II)), in the central cavity. The complexes are relatively well soluble in alcohols, a rare property for phthalocyanines. The bulky fluorinated side groups prevent stacking, providing an isolated nature of the paramagnetic centers. Moreover, these groups have a strong electron-withdrawing effect which enhances the Lewis acidity of the central metal. This leads to the coordination of solvent molecules to the central metal, resulting in a hexacoordination of the metal.

Devices based on MDMO-PPV are studied with electrically detected magnetic resonance (EDMR) to unravel the mechanisms underlying the organic magnetoresistance (OMAR) effect. In the EDMR experiments, different signals are observed and attributed to single charge carriers, i.e. holes and electrons. Both signals appear at the same threshold voltage where the OMAR signal reverses sign. Moreover, this bias voltage corresponds with the onset of bipolar transport. The correlation between the EDMR and the OMAR observations give a strong indication that the bipolaron mechanism is the dominant effect in OMAR, although other mechanisms cannot yet be excluded with certainty.