On the effective spin exchange in non-classical organic polymers

Ivanov, C.I.; Tyutyulkov, N.; Karabunarliev, Stoyan

doi:10.1016/0304-8853(90)90694-l

Cited by 24 publications

(4 citation statements)

References 51 publications

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“…With regard to early studies for infinite magnetic polymers, any ab initio crystal orbital investigations have not been reported, except our recent work for phenylenevinylene-bridged polymers with a methylene radical, 39 while only semiempirical treatments have already been carried out. [40][41][42][43][44][45][46][47][48][49][50][51] Judging from the previous result, 39 the DFT-based crystal orbital method may be a reasonable tool for theoretical studies of periodic polymers. However, the applicability of DFT computations to open shell systems such as organic radicals or transition metals has not been established sufficiently yet, although many approximated exchange and correlation functionals have also been proposed by various authors until now.…”

Section: Introductionmentioning

confidence: 77%

Density functional study of intramolecular ferromagnetic interaction through m-phenylene coupling unit (I): UBLYP, UB3LYP, and UHF calculations

Mitani¹,

Mori²,

Takano³

et al. 2000

The Journal of Chemical Physics

107

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Articles you may be interested inUnrestricted density functional theory based on the fragment molecular orbital method for the ground and excited state calculations of large systems Density functional theory with fractionally occupied frontier orbitals and the instabilities of the Kohn-Sham solutions for defining diradical transition states: Ring-opening reactions J. Chem. Phys. 111, 7705 (1999); 10.1063/1.480108Density functional study of intramolecular ferromagnetic interaction through m-phenylene coupling unit. III. Possibility of high-spin polymer Polyradicals comprised of m-phenylene-bridged organic radicals are well known as building blocks of organic ferromagnets, in which radical groups are connected with each other at the meta position in the benzene ring, and the parallel-spin configurations between radical sites are more stabilized than the antiparallel ones. Topological rules for spin alignments enable us to design organic high-spin dendrimers and polymers with the ferromagnetic ground states by linking various radical species through an m-phenylene unit. However, no systematic ab initio treatment of such spin dendrimers and magnetic polymers has been reported until now, though experimental studies on these materials have been performed extensively in the past ten years. As a first step to examine the possibilities of ferromagnetic dendrimers and polymers constructed of m-phenylene units with organic radicals, we report density functional and molecular orbital calculations of six m-phenylene biradical units with radical substituents and polycarbenes linked with an m-phenylene-type network. The relative stability between the spin states and spin density population are estimated by BLYP or B3LYP and Hartree-Fock calculations in order to clarify their utility for constructions of large spin denderimers and periodic magnetic polymers, which are final targets in this series of papers. It is shown that neutral polyradicals with an m-phenylene bridge are predicted as high-spin ground-state molecules by the computations, while m-phenylene-bridged ion-radical species formed by doping may have the low-spin ground states if zwitterionic configurations play significant roles to stabilize low-spin states. Ab initio computations also show an important role of conformations of polyradicals for stabilization of their high-spin states. The computational results are applied to molecular design of high-spin dendrimers and polymers. Implications of them are also discussed in relation to recent experimental results for high-spin organic molecules. d Standard geometries were assumed as CC and CH bond lengths and bond angles are 1.40 Å, 1.08 Å, and 120°, respectively. e J ab values by Eq. ͑11͒.

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Section: Introductionmentioning

confidence: 77%

Density functional study of intramolecular ferromagnetic interaction through m-phenylene coupling unit (I): UBLYP, UB3LYP, and UHF calculations

Mitani¹,

Mori²,

Takano³

et al. 2000

The Journal of Chemical Physics

107

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“…The energy gap between the HFB and the highest doubly occupied band (HDOB) of radical ion crystals consisting of naphthalene is equal to zero (see Figure 7). For that reason, the formalism in section 3.1 is not applicable to the calculation of the various contributions of the effective exchange integral J eff in the Heisenberg Hamiltonian (see eqs 2 and 3, and refs [28][29][30][31]. To obtain correct results of J eff one must consider additionally the elementary excitation between the HFB and the HDOB.…”

Section: δ(Imentioning

confidence: 99%

Nature of the Magnetic Interaction in Organic Radical Crystals. 5. Magnetic Interaction in Mixed Radical Ion Crystals

et al. 2001

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The nature and magnitude of the spin exchange interaction within the half-filled band of 1-D stacks of mixed radical ion crystals (MRIC) consisting of two hydrocarbons H 1 and H 2 with different ionization potentials and electron affinities have been investigated theoretically. In a fully reduced or oxidized 1-D crystal, each elementary unit is an anion radical or a cation radical: (H 1 ...H 2 ) •---or --(H 1 ...H 2 ) •+ --. In contrast to organic radical cation (anion) crystals which consist of identical polycyclic hydrocarbons -(H δ ‚‚‚H δ ) •+or -(H δ ‚‚‚H δ ) •-with a metalic or semiconducting ground state, the ground state of some classes of MRICs is a magnetic one. The band theory of magnetic interaction in many electron π-systems is applied to calculate the different contributions of the effective Heisenberg exchange integral.

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“…However, the magnitude of the indirect exchange Ž coupling of the model polymers investigated in . this article is essentially smaller in comparison w Ž with the exchange coupling expressed by J in- .x tra of -systems with intramolecular magnetic interaction-polymers with a continual -system Ž w x. of conjugation see, e.g., 23 . The absolute value of the exchange integral J is one order of magni- The character of the indirect interaction and the value of J is determined not only by the struci n d Ž .…”

Section: Numerical Results and Discussionmentioning

confidence: 99%

Organic polymers with indirect magnetic interaction caused by the symmetry of the elementary units

Tyutyulkov

Madjarova

Dietz

et al. 1998

Int. J. Quant. Chem.

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The magnetic properties of a class of 1-D -systems having a frontier Ž . half-filled band of degenerate MOs localized within the elementary units EU were studied theoretically. The localization of the MOs is caused by the symmetry of the -fragments which form the EUs. The localization and non-overlapping of the MOs Ž . results in vanishing of the direct Hund and the kinetic exchange interaction between Ž the unpaired electrons. The indirect exchange of the unpaired electrons spin-polarization . exchange occurs via the delocalized -electrons in the filled energy bands. An approach allowing the calculation of the indirect exchange interaction is applied for a class of polymers having pyrene, azulene, and s-indacene as fragments of the EUs. ᮊ

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On the effective spin exchange in non-classical organic polymers

Cited by 24 publications

References 51 publications

Density functional study of intramolecular ferromagnetic interaction through m-phenylene coupling unit (I): UBLYP, UB3LYP, and UHF calculations

Density functional study of intramolecular ferromagnetic interaction through m-phenylene coupling unit (I): UBLYP, UB3LYP, and UHF calculations

Nature of the Magnetic Interaction in Organic Radical Crystals. 5. Magnetic Interaction in Mixed Radical Ion Crystals

Organic polymers with indirect magnetic interaction caused by the symmetry of the elementary units

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