V.I. Krinichnyi

EPR study of spin and charge dynamics in slightly doped poly(3-octylthiophene)

An initial virgin plasticine-like poly(3-octylthiophene) (P3OT) and this sample modified by annealing and recrystallization were investigated at X-band (10 GHz) and mainly at D-band (140 GHz) electron paramagnetic resonance (EPR) in a wide temperature region. Paramagnetic centers with anisotropic magnetic-resonance parameters were proved to exist in all polymers, namely, mobile polarons whose concentration and susceptibility depend on the temperature and the polymer treatment. Superslow torsional motion of the polymer chains and layers was studied by the saturation transfer method at D-band EPR. Spin-spin and spin-lattice relaxation times were measured separately by the steady-state saturation method at the same waveband EPR. Intrachain and interchain spin diffusion coefficients and conductivity due to polaron dynamics were calculated. It was shown that the charge transport in P3OT is determined by the strong spin-spin interaction and is stimulated by torsion motion of the polymer chains. The total conductivity of P3OT is determined mainly by dynamics of paramagnetic charge carriers. Magnetic, relaxation and dynamics parameters of P3OT were also shown to change during the polymer treatment.

Spin charge carrier dynamics in poly(bis-alkylthioacetylene)

Initial and laser-irradiated poly(bis-alkylthioacetylene) (PATAC) samples were investigated by electron paramagnetic resonance (EPR) at X-band (9.6 GHz), Q-band (37 GHz), and D-band (140 GHz) in a wide temperature range. Two types of paramagnetic centers were proved to exist in laser-modified polymer, namely, localized and mobile polarons with the concentration ratio and susceptibility depending on the irradiation dose and temperature. Superslow torsion motion of the polymer chains was studied by the saturation transfer method at D-band EPR. Additional information on the polymer chain segment dynamics was obtained by the spin probe method at X-band EPR. Spin-spin and spin-lattice relaxation times were measured separately by the steady-state saturation method at D-band EPR. Intrachain and interchain spin diffusion coefficients and conductivity arising from the polaron dynamics were calculated. It was shown that the polaron dynamics in laser-modified polymer is affected by the spin-spin interaction. The interchain charge transfer is stimulated by torsion motion of the polymer chains, whereas the total conductivity of irradiated PATAC is determined mainly by the dynamic of diamagnetic charge carriers. Magnetic, relaxation and dynamics parameters of PATAC were also shown to change during polymer storage.

Spin relaxation studies on conducting poly(tetrathiafulvalene)

Magnetic parameters and the relaxation behavior of paramagnetic centers in an iodine-doped poly(tetrathiafulvalene) semiconductor with a d.c. conductivity of 10−5 S·cm−1 have been studied using mainly the 2 mm waveband EPR technique in the temperature range of 110–270 K. The EPR line shape analysis confirms the existence of immobile radicals pinne on short polymer chains and mobile polarons with different relaxation parameters in slightly doped poly(tetrathiafulvalene). The temperature dependences of electron spin-lattice and spin-spin relaxation times of paramagnetic centers of both types have been determined independently using the saturation method at the operation frequency νe = 140 GHz. An anisotropic slow libration of immobile polarons with an activation energy of 0.02 eV have been registered for the first time using the saturation transfer EPR method. The temperature dependences of intrachain diffusion and interchain hopping rates in poly(tetrathiafulvalene) are determined from theT1 andT2 EPR data. The interchain spin dynamics is shown to correlate with libration of polarons trapped on polymer chains and is in good agreement with a hopping charge transport mechanism.

Electronic properties of laser modified poly(bis-alkylthio-acetylene)

Abstract The laser-produced permanent electrical conductivity of the modified poly(bis-alkylthio-acetylene), PATAC, lies between 10 −5 and 200 Scm −1 depending on the sample preparation and the laser irradiation conditions. The electrical conductivity of the modified PATAC is long-time stable without any special protection. The converted polymers are p -type semiconductors. The Hall mobility has been estimated between 0.01 to 8 cm 2 V −1 s −1 . The temperature coefficient of the resistance in the highly conducting state is low and lies between 10 −3 and 10 −4 K −1 . ESR in the 2 mm and 3 cm waveband was applied for the study of the spin dynamics, and the rates of the intrachain and interchain spin charge carriers were obtained. Depending on the conditions of the conversion and the applied temperature the polymer shows typical properties either of a semiconductor or of a metal.

Polythiophene and polyacetylene conductors in the 3-cm and 2-mm ESR bands

Conclusions1.A dependence of the magnetic resonance parameters on the nature of the anion was established for organic polythiophene conductors with various anions.2.The major values of the anisotropic g-tensor were measured by 2-mm band ESR spectroscopy and the conductivity of polythiophene (BF4− and polyacetylene (I−) was evaluated at 200°K.

Very high field EPR study ofcis- andtrans-polyacetylene

Some neutralcis- andtrans-polyacetylene samples have been studied at 30–0.7 mm wave band EPR. A higher spectral resolution allows one to determine the principal values of anisotropicg-tensor of localized paramagnetic centers in polyacetylene, attributed to pinned neutral solitons. The Very High Frequency EPR allows us to observe the increase of a number of such centers and the appearance of soliton diffusion along the polymer chains after thecis-trans isomerization.

Charge transport in slightly doped polyaniline

The results of an experimental study of d.c. and microwave (140 GHz) conductivities of slightly HCl-doped polyaniline are presented. It was found that charge carriers hop between polaron states according to the Kivelsons theory.

Spin relaxation and magnetic properties of benzo-1,2,3-trithiolium radical cations

Magnetic and dynamics properties of paramagnetic centers in various trithiolium cations were characterized by static magnetic susceptibility measurements and EPR spectroscopy. Magnetically correlated units consisting of at least pairs of spins with ferromagnetic exchange coupling were found in some trithioles. The rates of intramolecular spin diffusion and intermolecular spin hopping were estimated separately. The rates and the anisotropy (v/v=20–300) of spin dynamics were shown to depend on the molecular structure.

Study of viscous liquids by spin micro- and macroprobe methods at 2-mm wave band EPR

The possibility of combined application of spin microprobe and macroprobe methods at 2-mm wave band EPR in determining the viscosity of a model system is demonstrated. Such an approach widens the range of dynamic viscosity EPR measurement in condensed systems and gives one the possibility to study separately various dynamic processes in a matrix.

2-MM waveband EPR macrospin probe method in the investigation of viscous condensed systems

Summary form only given. The suggested macrospin probe method based on the effect of a massive paramagnetic reorientation in a strong magnetic field allows one to study various condensed systems more correctly and accurately. The reorientational effect of a single crystal of an ion-radical salt based on dibenzotetrathiafulvalene (DBTTF)/sub 3/PtBr/sub 6/ of 5.10/sup - 5/ mm/sup 3/ volume volume in the solution (1:10) of nujol and nitroxide radical (10/sup -3/ M) in tery-buthylbenzene at magnetic field of H /spl tilde =/ 5 T is considered in the terms of one-point-fixed oscillator free turn in a dissipative system. The mechanical relaxation times of the macrospin probe rotation were determined and viscosities of its environment were evaluated near the melting temperature of the model system, when the phase transition is realized. Accompanied by the microspin probe, the method was shown to give the possibility to register separately or simultaneously both elastic deformation and a viscous flow of the same -matrix at the same temperature and time. The efficienty of the method, namely sensitivity, accuracy etc., is increased with a strength of magnetic field according to H/sup 5/ power law. Therefore, 2-mm wave band EPR is the exactly appropriate technique for the detailed investigation of various properties of condensed systems.