N. Tyutyulkov

Energy Spectra and Electric and Magnetic Properties of One-Dimensional Stacks of Conjugated π-Electron Systems with Defect Surface States. II. π-Systems with Schottky and Chemisorption Surface States

A rational new method for the synthesis of variable-sized Fe3O4 nanoparticles by aerial oxidation of Fe(OH)2 under visible light irradiation in the presence of trace EDTA has been investigated. The size of the Fe3O4 nanocrystals was controlled at about 11.5−30.0 nm by varying the reaction conditions in aqueous solution at room temperature. The oxidation reaction was significantly accelerated by visible light in the presence of EDTA. A rapid oxidation rate was favorable for decreasing the size of the Fe3O4 nanocrystals. The as-obtained Fe3O4 particles showed uniform spherical shape and a narrow size distribution. The variable-sized Fe3O4 nanocrystals exhibited different magnetic properties.

Nature of the magnetic interaction of Wurster's radicals in the solid state

Abstract The nature of the spin exchange interaction within the half-filled band in one-dimensional stacks of Wursters radicals in Wursters red bromide has been investigated theoretically. The various contributions to the Heisenberg effective exchange integral: direct, kinetic, and indirect spin exchange are evaluated quantitatively. It has been shown that the direct (Coulomb) exchange which causes the ferromagnetic coupling is small. The negative value of the effective exchange integral between Wannier functions, localized within the elementary units, has been determined by the kinetic and indirect (antiferromagnetic) exchange interaction.

Energy gap equation of 1D polyconjugated π-systems in the Hubbard approximation

Abstract It is shown that the energy gap of an arbitrary homonuclear or heteronuclear alternant or nonalternant π-conjugated system, having a singlet ground state, is given by the formula ΔEσ={Δ21(σ)corr+[Δ2(σ)corr+Δtop+Δgeom] 2} 1 2 , where Δtop and Δgeom are factors depending on the molecular topology and geometry, respectively. In the general case, the correlation corrections Δ1 (σ) and Δ2(σ) differ for MOs with different spin (σ=α,β) and ΔEβ≠ΔEβ. In some particular cases ΔEα= ΔEβ. The correlation correction Δ2(σ)corr corresponds to a non-uniform charge distribution in the π-system. In the case of homo-nuclear alternant systems Δ2(σ)corr=0. The investigations are carried out using the method of alternant molecular orbitals (AMO) in the Hubbard approximation. The band structure of the fully oxidized form of 1D poly(para-aniline)-poly(para-phenyleneimine), has been studied.

Influence of the long-range coulomb interaction upon the energy spectrum of infinite polyenes

AbstractIt is shown that the energies of AMOs (Ek) for an arbitrary homonuclear alternating system can be given with the following expression (identical for AMO with α- and β-spin):

STRUCTURE AND PROPERTIES OF NONCLASSICAL POLYMERS .9. NONALTERNANT POLYMERS

E_{k\sigma } = \alpha + \tfrac{1}{2}\gamma \pm (\delta ^2 \gamma ^2 + [e_k + \Delta _k (\gamma _{\mu v} )]^2 )^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} {\text{ }}\sigma \in \alpha ,\beta

Untersuchungen zum Energiespektrum vonα,ω-substituierten Polymethinketten

where: ek are the MO energies, obtained by means of the conventional HF method; δ and Δk are correlation corrections depending on the one-center (γ), resp. two-center (γμv) coulomb integrals.By means of the above method, where the interactions between non-adjacent AOs are taken into account, it is shown that the energy gap of an infinite polyene, in the π- electron approximation, is different from zero, regardless of the presence or absence of C-C bond alternation. This means that in adiabatic approximation an infinite atomic chain, satisfying the Born-Karman condition, is not a metal model but a dielectric one.

Photoswitching of dipole moments, charge-transfer and spectroscopic properties

Abstract The change of the magnetic properties of the isomeric forms of photoresponsive model polymers with photochromic diarylethene elementary units substituted with radical centers are investigated theoretically. The band theory is used to calculate the effective exchange integral of the photoisomeric one-dimensional many-electron π-systems. It is shown that the magnetic properties can be reversibly switched from ferromagnetic to non-magnetic in some cases. In other cases the magnitude of the ferromagnetic exchange interaction is either increased or decreased in the photoisomers. The practicability of the photocyclization is estimated using reactivity indices in the excited state calculated in π-electron approximation with the HMO method. In most cases a reversible photocyclization (ring opening) should be possible.

Energy spectra of the poly[peri-acene]s: analytical solution of the LCAO MO problem

SummaryThe investigations on alternant non-classical (non-Kekulé) polymers [1, 2] (ANCP) have been extended to a class of quasi-one-dimensional non-alternant non-classical polymers (NANCP).The energy spectra and the effective spin exchange between the unpaired electrons in the NANCP are investigated theoretically.As for the ANCP, the energy spectrum of the NANCP is characterized by a wide energy gap in which there is a half-filled band (HFB) of degenerate non-bonding molecular orbitals (NBMO).The occurrence of a NBMO is a topological property of the considered non-alternant systems, and is explained with an approach which originates from the Sachs theorem.The effective spin exchange interaction within the HFB of a wide variety of model polymers was calculated. It is shown that the potential (Coulomb) and the indirect exchange interaction (superexchange) are the main components of the effective ferromagnetic interaction. The ground state of the 1D-NANCP is a high-spin one, as in the case of the ANCP.