Recently, much attention has been paid to the synthesis and investigation of nanocomposites based on conjugated fluorene-thiophene-benzothiadiazole (FOT, TBT, DBT) copolymers with alternating electron-donor and electron-acceptor units. This is mainly due to their higher efficiency (6-7%) of converting solar energy into electrical energy, as well as photochemical and temperature stability. When heterojunctions of such copolymers with methanofullerenes are illuminated, photoinduced separation and charge transfer by spin carriers, polarons, and anion radicals of methanofullerene take place. This allows one to investigate the spin-dependent relaxation, magnetic, dynamic, and other properties of such systems by the direct method of light induced EPR (LEPR).

In this work we analyze the results of LEPR study of processes curring out with spin charge carriers in bulk heterojunctions of narrow-band copolymers of poly poly[(9,9-dioctylfluorenyl-2.7-diyl)-co-(bithiophene)] (PFOT), poly[2,7-(9,9-dioctylfluorene)-alt-4,7-bis(thiophen-2-yl)benzo-2,1,3-thiadiazole] (PFO-DBT) and poly[N-9'-hepta-decanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT) with [6,6]-phenyl-C61-butanoic acid (PCBM) over a wide range of temperatures (77-320 K) and the initiating light photons energy (1.32-3.14 eV).

The composition and concentrations of charge carriers are determined by deconvolution of effective FEPR spectra. The relaxation parameters of charge carriers are separately determined using the method of continuous microwave saturation of spin packets.

It is shown that some of the photo-initiated polarons are trapped by spin traps reversibly arising upon irradiation in a copolymer matrix whose quantity and energy depth are determined by the structure of the copolymer nanocomposite. The dependence of the magnetic, relaxation and dynamic parameters of charge carriers on the spin packet's exchange interaction, as well as the localization of polarons by energy traps in the copolymer matrix, are established. It is shown that the structure and specific morphology of nanocomposites predetermine the essential dependence of their electronic dynamic parameters on the energy of the exciting photons. The higher ordering of the structure of the PCDTBT:PCBM nanocomposite in comparison with others, leads to a decrease in the number of spin traps and the order of the spin carriers recombination process.

The ways of creating new elements of molecular electronics and spintronics based on the studied nanocomposites are considered.