A Functional Nitroxide Radical Displaying Unique Thermochromism and Magnetic Phase Transition

Matsumoto, Sachiko; Higashiyama, Tsutomu; Akutsu, Hiroki; Nakatsuji, Shin’ichi

doi:10.1002/ange.201104068

Cited by 6 publications

(2 citation statements)

References 15 publications

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“…Because of the large difference in bond lengths between SS and WS state (unit cell volume changes by up to 13%) and the high mechanical stability during switching, these crystals have been described as “breathing”. Apart from breathing crystals, several other examples (including very recent ones) of interesting magnetic behavior in compounds based on copper(II) and/or nitroxides have been reported. − …”

Section: Introductionmentioning

confidence: 99%

W-Band Time-Resolved Electron Paramagnetic Resonance Study of Light-Induced Spin Dynamics in Copper–Nitroxide-Based Switchable Molecular Magnets

et al. 2012

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Molecular magnets Cu(hfac)(2)L(R) represent a new type of photoswitchable materials based on exchange-coupled clusters of copper(II) with stable nitroxide radicals. It was found recently that the photoinduced spin state of these compounds is metastable on the time scale of hours at cryogenic temperatures, similar to the light-induced excited spin state trapping phenomenon well-known for many spin-crossover compounds. Our previous studies have shown that electron paramagnetic resonance (EPR) in continuous wave (CW) mode allows for studying the light-induced spin state conversion and relaxation in the Cu(hfac)(2)L(R) family. However, light-induced spin dynamics in these compounds has not been studied on the sub-second time scale so far. In this work we report the first time-resolved (TR) EPR study of light-induced spin state switching and relaxation in Cu(hfac)(2)L(R) with nanosecond temporal resolution. To enhance spectral resolution we used high-frequency TR EPR at W-band (94 GHz). We first discuss the peculiarities of applying TR EPR to the solid-phase compounds Cu(hfac)(2)L(R) at low (liquid helium) temperatures and approaches developed for photoswitching/relaxation studies. Then we analyze the kinetics of the excited spin state at T = 5-21 K. It has been found that the photoinduced spin state is formed at time delays shorter than 100 ns. It has also been found that the observed relaxation of the excited state is exponential on the nanosecond time scale, with the decay rate depending linearly on temperature. We propose and discuss possible mechanisms of these processes and correlate them with previously obtained CW EPR data.

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Section: Introductionmentioning

confidence: 99%

W-Band Time-Resolved Electron Paramagnetic Resonance Study of Light-Induced Spin Dynamics in Copper–Nitroxide-Based Switchable Molecular Magnets

et al. 2012

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“…Most of the bistable compounds so far reported are based on transition metal ions [7][8][9] , but recent work 10 strongly suggests that organic radicals can also be at the forefront in the design and fabrication of the next generation of sensors and devices. Indeed, thiazyl- 11,12 , spiro-biphenalenyl- 13 and nitroxide-based radicals 14,15 have furnished striking examples of metal-free bistable materials whose phase transitions are accompanied by changes in the magnetic, optical and/or electrical response.…”

mentioning

confidence: 99%

The key role of vibrational entropy in the phase transitions of dithiazolyl-based bistable magnetic materials

et al. 2014

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The neutral radical 1,3,5-trithia-2,4,6-triazapentalenyl (TTTA) is a prototype of moleculebased bistable materials. TTTA crystals undergo a first-order phase transition between their low-temperature diamagnetic and high-temperature paramagnetic phases, with a large hysteresis loop that encompasses room temperature. Here, based on ab initio molecular dynamics simulations and new X-ray measurements, we uncover that the regular stacking motif of the high-temperature polymorph is the result of a fast intra-stack pair-exchange dynamics, whereby TTTA radicals continually exchange the adjacent TTTA neighbour (upper or lower) with which they form an eclipsed dimer. Such unique dynamics, observed in the paramagnetic phase within the whole hysteresis loop, is the origin of a significant vibrational entropic gain in the low-temperature to high-temperature transition and thereby it plays a key role in driving the phase transition. This finding provides a new key concept that needs to be explored for the rational design of novel molecule-based bistable magnetic materials.

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Self‐Assembling Aryl‐Naphthalendiimide Derivatives with a Nitroxide Radical

et al. 2012

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A series of aryl‐substituted naphthalenediimide derivatives that contain nitroxide radicals were prepared and their crystal structures were elucidated. Much stronger charge‐transfer interactions were present in the derivatives with perfluorobenzene substituents than those with phenyl or 4‐fluorophenyl substituents. These interactions result in the formation of single‐component charge‐transfer complexes by self‐assembly of the naphthalenediimide derivatives to provide black crystals. As a consequence, the naphthalenediimide derivatives with perfluorobenzene substituents have better field‐effect transistor (FET) properties than the other derivatives.

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A Functional Nitroxide Radical Displaying Unique Thermochromism and Magnetic Phase Transition

Cited by 6 publications

References 15 publications

W-Band Time-Resolved Electron Paramagnetic Resonance Study of Light-Induced Spin Dynamics in Copper–Nitroxide-Based Switchable Molecular Magnets

W-Band Time-Resolved Electron Paramagnetic Resonance Study of Light-Induced Spin Dynamics in Copper–Nitroxide-Based Switchable Molecular Magnets

The key role of vibrational entropy in the phase transitions of dithiazolyl-based bistable magnetic materials

Self‐Assembling Aryl‐Naphthalendiimide Derivatives with a Nitroxide Radical

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