Computational design of the magnetism-tunable oligobenzylic carbanion complexes

Yang, Hongfang; Zhao, Jing; Song, Xinyu; Bu, Yuxiang

doi:10.1007/s00214-014-1460-2

Cited by 6 publications

(10 citation statements)

References 36 publications

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“…As shown in Figures S1 and S2, the optimized molecular geometries indicate that in 1a two nitroxide radicals are coplanar with the p-pyrazinyl coupler, which is a typical Kekule structure, and the extensive πconjugation is developed between two ⟩NO • groups and the coupler, and therefore delocalization of the π-type unpaired electrons plays an essential role in determining the magnitude and sign of magnetic exchange couplings. 38 A great fraction of spin density is delocalized from the two ⟩N−O • centers to the coupler, further suggesting the formation of the extended πconjugation (see 1a-BS in Figure 3), which potentially provides a feasible means of spin transport 56 and facilitates a strong antiferromagnetic coupling. Although the coupler has aromaticity (the calculated NICS(0) and NICS(1) value at a point 1 Å above the center of coupling ring are 1.0607 and −3.5454 ppm, respectively), which is in favor of ferromagnetic coupling, 38 delocalization of π-electrons is dominant in this conjugated system.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Clearly, these results are in good agreement with those estimated from the corresponding ⟨S 2 ⟩ values (0.644, 0.977, 0.985, and 0.547), further confirming the accuracy of our computational results. 56 As for the above-mentioned other two couples of diradical molecules, 1a′/1b′ and 2a′/2b′, their properties of magnetic couplings and magnetic transformations are exactly alike with their corresponding stereoisomer couples, 1a/1b and 2a/2b, and thus we will not discuss them. To further understand the magnetic properties and their relationship with molecular structures of these designed organic molecules, in the following sections, we analyze the magnetic characteristics from three aspects: spin alternation rule, SOMO effect, and SOMO− SOMO energy gap of the triplet state.…”

Section: ■ Introductionmentioning

confidence: 99%

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Redox-Modulated Magnetic Transformations between Ferro- and Antiferromagnetism in Organic Systems: Rational Design of Magnetic Organic Molecular Switches

Zhang

Song

2015

J. Phys. Chem. C

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Organic molecules with switchable magnetic properties have extensively technological applications due to the fact that magnetic conversion can be realized through diverse methods. In particular, the redox-induced magnetic reversal is easy to accomplish and exhibits promising application in the field of magnetic materials, and thus it is an imperative task to find magnetism-switchable systems. Herein, we computationally design two couples of nitroxy–pyrazinyl–nitroxy diradicals in which two nitroxy radical groups are connected to a redox-active pyrazinyl coupler in the para or meta modes. We find that the magnetic conversion can occur from ferromagnetic to antiferromagnetic exchange coupling or vice versa by means of the redox method in these designed magnetic organic molecules, and their magnetic exchange coupling constants are considerably large no matter for ferromagnetic or antiferromagnetic couplings, as evidenced at both the B3LYP and M06-2X levels of theory. Analyses indicate that redox-induced structural change of the coupler leads to conversion of its aromaticity and considerable spin delocalization from the π-conjugated structure and spin polarization from non-Kekule structure, which thus determine the spin coupling between two spin centers in the magnetic molecules. In addition, the spin alternation rule, singly occupied molecular orbital (SOMO) effect, and SOMO–SOMO energy splitting of triplet state are utilized to analyze the diradical characters of the molecules, suggesting effective tools for predicting molecular ground states (ferromagnetic, antiferromagnetic, or nonmagnetic). This work provides helpful information for the rational design of promising organic magnetic switches.

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Section: ■ Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

Redox-Modulated Magnetic Transformations between Ferro- and Antiferromagnetism in Organic Systems: Rational Design of Magnetic Organic Molecular Switches

Zhang

Song

2015

J. Phys. Chem. C

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“…Furthermore, diradical characters of all magnetic molecules are predicted quantitatively by the CASSCF(10,10)/6‐311++G(d,p) method. Apparently, just as we can see from Table S5 (in the SI), the results are in good agreement with those estimated from the corresponding <S 2 > BS values, further proving the accuracy of our computational results …”

Section: Resultsmentioning

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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“…In view of the successful and a vast number of applications of B3LYP functional in optimizing molecular geometries and examining diradical character, ,,− herein, we perform a B3LYP functional calculational analysis to obtain a basic understanding of potential diradical character in HAP that appears due to molecular thermal vibrations. Thus, the geometries of CS and T states of static HAP were fully optimized by using the UB3LYP/6-311++G(d, p) method. , The optimized geometries were further verified to be local minima through vibrational analyses, which show no imaginary frequency vibrational mode.…”

Section: Computational Detailsmentioning

confidence: 99%

Molecular Vibrations Induced Potential Diradical Character in Hexazapentacene

et al. 2016

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While the photoelectrochemical behavior of azapentacene has been investigated successfully, insight into the dynamic electronic properties of azapentacene triggered by different energy pulses is very scarce. The present work reports a fascinating phenomenon about potential diradical character governed by structural vibrations in hexazapentacene. In complete contrast to the static equilibrium configuration of hexazapentacene without diradical character, due to the vibration-based structural perturbation, DFT calculations show that some of the transient configurations possess diradical character and thus magnetism, which exhibit different periodic pulse behavior in time evolution. Since each vibrational mode refers to two distortion ways (positive/negative distortions from equilibrium configuration), 7 different possibilities are observed for the vibrationinduced diradical character for all vibrational modes (e.g., a combination of nonradical, singlet diradical, or triplet diradical for positive distortion and those of for negative distortion for each vibrational mode). This intriguing diradical character is rationalized by structural distortions with considerable changes of some energy quantities. The structural distortions cause the HOMO energy raising and LUMO energy lowering and thus an efficient reduction of the HOMO−LUMO energy gap and singlet−triplet gap of the system, which are favorable to the formation of the broken-symmetry open-shell singlet or triplet states. The periodic pulsing behavior is attributed to persistent molecular vibrations and is thus vibrational mode controlled. Compared with pentacene, the remarked effects of nitrogen substitution on the diradical properties and their pulsing behaviors are mainly due to the decreases of both the HOMO and the LUMO energies and considerable narrowing of their gaps in the vibrationsdistorted configurations. This intriguing potential diradical character and its different dynamic behavior suggest hexazapentacene potential applications as promising building blocks in the rational design of novel electromagnetic materials because of its controllable magnetism through energy pulses. This work provides comprehensive understanding of the nature of dynamic variations of the electronic structures and properties of the nitrogen-rich acene derivatives and other materials molecules.

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Computational design of the magnetism-tunable oligobenzylic carbanion complexes

Cited by 6 publications

References 36 publications

Redox-Modulated Magnetic Transformations between Ferro- and Antiferromagnetism in Organic Systems: Rational Design of Magnetic Organic Molecular Switches

Redox-Modulated Magnetic Transformations between Ferro- and Antiferromagnetism in Organic Systems: Rational Design of Magnetic Organic Molecular Switches

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

Molecular Vibrations Induced Potential Diradical Character in Hexazapentacene

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