Intramolecular ferromagnetic coupling in bis-oxoverdazyl and bis-thioxoverdazyl diradicals with polyacene spacers

Bhattacharya, Debojit; Shil, Suranjan; Misra, Anirban; Klein, Douglas J.

doi:10.1007/s00214-009-0705-y

Cited by 43 publications

(47 citation statements)

References 93 publications

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“…That is, the J value of a diradical can be estimated by simply determining the exact singlet and triplet state energies. It is known that a single determinantal wave functional in the unrestricted Hartree–Fock (UHF) methodology can be utilized to accurately describe the triplet geometry, but it cannot truly represent the singlet of a diradical due to the introduction of spin contamination . Therefore, this method cannot yield credible J values.…”

Section: Computational Detailsmentioning

confidence: 99%

Intriguing diaza effects on magnetic coupling characteristics in diaza‐benzo[k]tetraphene‐bridged nitroxide diradicals

Zhang

Luo

Song

et al. 2018

Int J of Quantum Chemistry

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We theoretically design four diaza‐benzo[k]tetraphene‐based diradical isomers (1, 2, 3, and 4) with two nitroxide (NO) radical groups as spin sources. The calculations at the B3LYP/6‐311++G(d,p) level suggest that the diaza doping can induce the aromaticity changes and the CC bond rearrangements and, thus, remarkably affect their magnetic coupling magnitudes and even characteristics (ferromagnetic vs. antiferromagnetic). More interestingly, different diaza‐doping positions can lead to distinctly different effects, and further dielectron‐oxidation can also noticeably change the magnetic coupling magnitudes from −919.9 cm−1 (1) to −158.3 cm−1 (1 2+) or from −105.1 cm−1 (3) to −918.9 cm−1 (3 2+) or induce the magnetic conversions from nonmagnetism (2) to antiferromagnetism (2 2+, −140.1 cm−1) or from ferromagnetism (4, 108.9 cm−1) to antiferromagnetism (4 2+, −462.5 cm−1). Good matching of two singly occupied molecular orbitals (SOMOs) of the NO groups with the highest occupied molecular orbital (HOMO) of the coupler (for 1), or with the lowest unoccupied molecular orbital (LUMO) of the coupler (for 3 2+ and 4 2+), available Kekulé structure (for 2), aromaticity variations are responsible to strong magnetic couplings. Besides, the HOMO‐LUMO energy gaps of the couplers also considerably affect the magnetic couplings. This work may open a new route for the rational design of the diaza‐benzo[k]tetraphene‐based magnetic molecular modulators or switches.

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Section: Computational Detailsmentioning

confidence: 99%

Intriguing diaza effects on magnetic coupling characteristics in diaza‐benzo[k]tetraphene‐bridged nitroxide diradicals

Zhang

Luo

Song

et al. 2018

Int J of Quantum Chemistry

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“…6-Thioxoverdazyl derivatives, discovered several decades ago, [6][7][8] still remain little explored, [9] presumably due to the challenging and low-yielding synthesis. However, recent papers indicate renewed interest in these radicals with the focus on their magnetic [10][11][12][13] and metal-complexing properties. [14] It is also expected that sulphur-containing derivatives will exhibit enhanced charge transport properties in supramolecular assemblies.…”

Section: Introductionmentioning

confidence: 98%

Bent-core 6-thioxoverdazyl: a comparison of mesogenic properties with the 6-oxo analogue

2015

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Two bent-core verdazyl radicals, 2[16] and 3 [16], containing 6-thioxo and 6-oxo groups, respectively, were prepared and their physical properties were compared. Analysis of binary mixtures with bent-core mesogen 1[12] gave virtual N-I ([T NI ]) and N-I re ([T NIre ]) transition temperatures. Results indicate that the thioxo derivative 2[16] has greater stabilising effect on the nematic phase than the 6-oxo analogue 3[16], presumably due to the higher dipole moment of the core (1.90 D vrs 0.83 D) despite the less favourable conformational properties.

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“…The crucial role of the couplers between two radicals on the sign and magnitude of the exchange coupling constants has recently come to light. The phenylene as a coupler has been widely discussed, finding that the m ‐phenylene linking mode tends to favor ferromagnetic (FM) coupling while the p ‐phenylene mode tends to favor antiferromagnetic (AFM) one. Bhattacharya et al .…”

Section: Introductionmentioning

confidence: 99%

Tuning the Spin Coupling Interactions in the Nitroxide‐Based Bisphenol‐Like Diradicals

Song

2017

ChemPhysChem

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The intramolecular spin coupling interactions of bisphenol-like trinary-bridged diradicals [nitroxide-(para/meta)phenylene-X-phenylene(para/meta)-nitroxide, X=C=CH , O, BH, NH and SO ] were explored with an emphasis on the tuning role of the X coupler at the (U)B3LYP/6-311++G(d,p) level. Our results indicate that all designed trinary-bridged diradicals featuring a V-type structure with a bending angle of 104-130° and torsional angles of two phenylene rings being 20-90° exhibit different diradical character and magnetism, depending on the structures and properties of the X bridges. More interestingly, although meta/para-phenylene supports a ferromagnetic (FM)/antiferromagnetic (AFM) coupling, their combinations by using X as a trinary bridge can mediate spin coupling, but the coupling magnitude strongly depends on X. In general, a para/para or meta/meta combination with X leads to an open-shell singlet ground state and thus AFM, but the meta/meta combination considerably decreases the spin coupling interaction. In contrast, a para/meta combination with X produces a triplet ground state and FM. Their combination with a single-electron conjugation end coupler (C=CH ) leads to an inverse coupling regularity. All results can be reasonably explained by the spin alternation rule, molecular structures, and properties. In particular, detailed spin coupling mechanisms are suggested to involve cooperative through-space and through-bond pathways with different levels of cooperativity. This is rationalized with the X-induced bending of the diradicals not only modifying the through-bond (extended π conjugation) pathway but also provididng a through-space (face-to-face vs. side-to-side π-π interaction) possibility for spin coupling, in conjunction with twisting of the phenylene rings. Different contributions of the through-space and through-bond couplings are quantitatively distinguished and depend on the structure and property of the X coupler. Clearly, this work reports interesting aspects of the trinary bridged diradicals and also provides important information for the design of molecules for functional magnetic materials and tuning their magnetic properties.

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Intramolecular ferromagnetic coupling in bis-oxoverdazyl and bis-thioxoverdazyl diradicals with polyacene spacers

Cited by 43 publications

References 93 publications

Intriguing diaza effects on magnetic coupling characteristics in diaza‐benzo[k]tetraphene‐bridged nitroxide diradicals

Intriguing diaza effects on magnetic coupling characteristics in diaza‐benzo[k]tetraphene‐bridged nitroxide diradicals

Bent-core 6-thioxoverdazyl: a comparison of mesogenic properties with the 6-oxo analogue

Tuning the Spin Coupling Interactions in the Nitroxide‐Based Bisphenol‐Like Diradicals

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