The role of spin exchange in charge transfer in low-bandgap polymer: Fullerene bulk heterojunctions.

Formation, relaxation and dynamics of polarons and methanofullerene anion radicals photoinitiated in poly[N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)]:-[6,6]-phenyl-C61-butyric acid methyl ester (PCDTBT:PC61BM) bulk heterojunctions were studied mainly by light-induced EPR (LEPR) spectroscopy in wide photon energy and temperature ranges. Some polarons are pinned by spin traps whose number and depth are governed by the composite morphology and photon energy. The proximity of the photon energy and the polymer bandgap reduces the number of such traps, inhibits recombination of mobile charge carriers, and facilitates their mobility in polymer network.

Light-induced EPR study of charge transfer in poly(3-hexylthiophene)/fullerene bulk heterojunction.

The first results of the light-induced EPR study of magnetic, relaxation, and dynamic parameters of charge carriers background photoinduced by optical photons (1.7-3.4 eV) in poly(3-hexylthiophene)/fullerene bulk heterojunctions are described.

2 mm waveband saturation transfer electron paramagnetic resonance of conducting polymers.

The 2 mm waveband (140 GHz) saturation transfer electron paramagnetic resonance (ST-EPR) spectroscopy has been employed to characterize the very slow microsecond to millisecond librational macromolecular dynamics of a wide range of conducting polymers. It is possible at this waveband to determine separately spin relaxation and dynamics affecting ST-EPR spectra. Higher microwave frequency provides substantial increases sensitivity of the method to the anisotropic macromolecular motion in conducting polymers and broadens the interval of correlation times up to 1-80 ms, thereby extending the slow-motion limit for ST-EPR by two orders of magnitude compared with convenient wavebands EPR.

The 140-GHz (D-band) saturation transfer electron paramagnetic resonance studies of macromolecular dynamics in conducting polymers.

The high-field/high-frequency (5 T, 140 GHz) saturation transfer electron paramagnetic resonance (ST-EPR) method was used for the study of superslow librational macromolecular dynamics in various conducting polymers. It was shown that the increase of the electron precession frequency allows separate determination of spin relaxation and dynamics differently affecting effective ST-EPR spectra. Higher microwave frequency increases significantly the spectral resolution of the method and its sensitivity to the anisotropic macromolecular motion in conducting polymers.

The effect of fullerene derivative on polaronic charge transfer in poly(3-hexylthiophene)/fullerene compound.

The effect of a structure of a fullerene derivative on electronic properties of poly(3-hexylthiophene)/fullerene composite was studied at 3 cm wave band EPR in wide (77-320 K) temperature region. All the systems with different fullerene derivatives demonstrate sum spectrum of small polarons with different mobilities and contributions depending on the structure of the fullerene derivative. Both the spin-lattice and spin-spin relaxation times were determined separately by using the steady-state saturation method.

Investigation of biological systems by high resolution 2-mm wave band ESR.

The application of high resolution ESR to the investigation of various biological systems is discussed. The advantages of the technique in the study of structural, conformational and dynamic characteristics have been exemplified by spin-labeled human serum albumin, egg lysozyme, liposome membranes, inverted micelles, alpha-chymotrypsin, cotton fiber and cellulose. The polarity of the microenvironment and the mechanism of molecular mobility of the objects under study have been determined.

[Study of lysozyme by a spin-label method in the 2-mm range].

Two millimeter range ESR-spectroscopy was used to measure the values of magnetic resonance parameters of egg lysozyme samples modified with nitroxyl label 4-(iodine-acetamide)-2,2,6,6-tetramethylpiperidine-1-oxyl by hist-15 residue. It has been shown that in a lyophilic sample the spin label forms a hydrogen bond with the protein group and when the sample is moistened--with water molecules. Temperature changes of the pattern of ESR line are analysed.

[Study of molecular mobility in biological membranes by 2-mm band ESR spectroscopy].

Temperature relationship was measured of ESR spectra of spin probes--derivatives of fatty acids whose nitroxyl fragments are incorporated into surface and inner layers of phosphatidylcholine liposomes (T = 180-260 K), as well as of the probe in model ethanol solution (T = 110-220 K). Data on the nature and rotation frequency of probe nitroxyl fragments were obtained from the analysis of the spectra. It was shown that the frequency of the probes movement in the systems under study corresponds to the slow movement region, i.

[Study of the effect of the microenvironment on magnetic resonance parameters of spin-labeled human serum albumin in a 2-mm ESR range].

Basic values of g-tensor and Azz component of HF tensor of two spin labels and spin probe on HSA and nitroxyl radicals HO-15, HO-34 in the solvents of different polarity were measured by 2 mm band ESR of 2 mm range. Magnetic-resonance parameters of liophylized and water-solved spin-labeled HSA were shown to correspond to the parameters of the solvents of the label HO-15 and HO-34 in ethyl alcohol and water. A conclusion was drawn concerning the identity of microenvironment of the nitroxyl fragment of liophylized HSA and frozen solution of the label HO-15 and HO-34 in ethyl alcohol and solvatation of the nitroxyl fragment of spin-labeled HSA and label HO-15 (HO-34) by water molecules.