Studies of organic di-, oligo-, and polyradicals by means of their bulk magnetic properties

Iwamura, Hiizu; Koga, Noboru

doi:10.1021/ar00030a008

Cited by 248 publications

(112 citation statements)

References 46 publications

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“…The discussion in this chapter has been specialized and limited, in view of our aims firstly to identify the features of organic radicals that can help or hinder the assembly of organic ferromagnetic materials and secondly to lay a foundation for more detailed discussion of the electronic and magnetic states of these systems. Complementary discussions of organic radicals and molecular magnetic states are given by Iwamura [71], Buchachenko [72], and Iwamura and Koga [73].…”

Section: Molecular Design and Molecular Magnetsmentioning

confidence: 99%

Chapter 2: Organic Molecules, Radicals, and Spin States

Datta¹,

Trindle²,

Illas³

2014

Theoretical and Computational Aspects of Magnetic Organic Molecules

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Section: Molecular Design and Molecular Magnetsmentioning

confidence: 99%

Chapter 2: Organic Molecules, Radicals, and Spin States

Datta¹,

Trindle²,

Illas³

2014

Theoretical and Computational Aspects of Magnetic Organic Molecules

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“…Theoretical studies on the magnetic nature of these molecules and the effect of the magnetic field on some of these systems have been carried out by many researchers. [1][2][3][4][5] However, the most interesting research area to emerge has been the design of organic systems, especially molecular crystals with desirable magnetic properties. The ferro-or antiferromagnetic properties of a few molecular crystals composed of molecules with unpaired spins have already been characterized by Awaga and Maruyama, 6 Azuma et al 7a and Allemand et al 7b on the basis of the simple one-dimensional chain model introduced by McConnell.…”

Section: Introductionmentioning

confidence: 99%

On the ferromagnetic and antiferromagnetic properties of molecular crystals

Datta

Misra

1999

The Journal of Chemical Physics

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Ferro-and antiferromagnetic molecular crystals are in several ways quite distinct from the conventional metallic alloys or oxidic crystals studied in solid state physics. The exchange coupling constants are usually very small for crystals of free radical molecules. Some molecular crystals show a typical magnetic behavior at a very low temperature range and another kind of behavior at a higher temperature. This feature cannot be quantitatively explained by using the conventional Ising model of ferromagnetic ͑FM͒ and antiferromagnetic ͑AFM͒ materials. In this work we show that a magnon-based approach is capable of explaining the observed AFM→FM and FM→AFM transitions in crystals of free radical molecules in a natural manner. A three-dimensional lattice is, in general, anisotropic in magnetic properties. For instance, in a molecular crystal, FM interactions may be observed along a particular direction while AFM interactions dominate along the others. Also, the coupling constants can vary widely along the three crystal axes. We have classified ferroand antiferromagnetic molecular crystals into four distinct types, viz., FFF, AFF, AAF, and AAA, for orthorhombic or higher crystal symmetries. The anisotropic Heisenberg spin Hamiltonian operators for these four systems have been expressed in terms of magnon variables. The magnon dispersion relations have been determined, and by using these relationships the magnon population has been calculated for the low temperature range as well as for the medium and high temperature ranges. These calculations rely on the choice of the population distribution function. The low temperature calculation involves the Planck distribution. Since the magnon-magnon interaction increases very rapidly above the Neél temperature, we have made use of the classical limit, that is, a Boltzmann distribution for each spin site, and the zeroth-order one-magnon energy to calculate the magnon population at higher temperature ranges. All these calculations are based on the consideration of a macroscopically large crystal of a specific shape, and the validity of the results rests on the assumption that the bulk magnetic properties remain unchanged for a macroscopically large crystal of any other shape. Then we have derived expressions for the overall magnetization in macroscopically large crystals of the four types in the two temperature ranges, and the corresponding magnetic susceptibilities ͑ ͒. In doing so, we have made use of a typical Weiss molecular field in each case. The resulting expressions are general enough, that is, they are for an anisotropic crystal and remain valid in wide ranges of temperature. They also agree with available experimental data. The FFF and the AAA systems do not exhibit any unusual trend. As T→0, the FFF system attains saturation whereas the AFF, AAF, and AAA systems all show an approximate T 2 dependence of ʈ . At a sufficiently high temperature, all four types exhibit bulk paramagnetism that follow the Curie-Weiss-type law. The FFF susceptibility develops a characterist...

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“…The delocalized p orbital network is most important in determining the spin states in the photoexcited states [1][2][3] and ground states. [4][5][6] Spin manipulation is a challenging topic in the field of molecular magnetism. [7,8] We earlier reported spin manipulation using the photoexcited molecular field in purely organic p-conjugated spin systems, in which parallel alignment of two pendant radical spins through an excited triplet spin coupler leads to the photoexcited quintet (S = 2) high-spin state.…”

mentioning

confidence: 99%

π Topology and Spin Alignment in Unique Photoexcited Triplet and Quintet States Arising from Four Unpaired Electrons of an Organic Spin System

Teki

Toichi

Nakajima

2006

Chemistry A European J

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Syntheses, electronic structures in the ground state, unique photoexcited states, and spin alignment are reported for novel biradical 1, which was designed as an ideal model compound to investigate photoinduced spin alignment in the excited state. Electron spin resonance (ESR), time-resolved ESR (TRESR), and laser-excitation pulsed ESR experiments were carried out. The magnetic properties were examined with a SQUID magnetometer. In the electronic ground state, two radical moieties interact very weakly (almost no interaction) with each other through the closed-shell diphenylanthracene spin coupler. On photoirradiation, a novel lowest photoexcited state with the intermediate spin (S = 1) arising from four unpaired electrons with low-lying quintet (S = 2) photoexcited state was detected. The unique triplet state has an interesting electronic structure, the D value of which is reduced by antiferromagnetic spin alignment between two radical spins through the excited triplet spin coupler. The general theoretical predictions of the spin alignment and the reduction of the fine-structure splitting of the triplet bis(radical) systems are presented. The fine-structure splitting of the unique photoexcited triplet state of 1, as well as the existence of the low-lying quintet state, is interpreted well on the basis of theoretical predictions. Details of the spin alignment in the photoexcited states are discussed.

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Studies of organic di-, oligo-, and polyradicals by means of their bulk magnetic properties

Cited by 248 publications

References 46 publications

Chapter 2: Organic Molecules, Radicals, and Spin States

Chapter 2: Organic Molecules, Radicals, and Spin States

On the ferromagnetic and antiferromagnetic properties of molecular crystals

π Topology and Spin Alignment in Unique Photoexcited Triplet and Quintet States Arising from Four Unpaired Electrons of an Organic Spin System

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