Photoinduced Cooperative Charge Transfer in Low-Dimensional Organic Crystals

Koshihara, Shin‐ya; Takahashi, and Yosuke; Sakai, Hiroto; Tokura, Y.; Luty, Tadeusz

doi:10.1021/jp984172i

Cited by 220 publications

(181 citation statements)

References 29 publications

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“…The large concentration of Fe vacancies in this crystal, which might otherwise be thought to be a shortcoming of this material, is an essential prerequisite for the reversible transformations. The present model also implies that the photoinduced change must be a cooperative phenomenon [15,[21][22][23], because the structural change of the entire crystal is induced by excitations in a fraction of the crystal. To confirm our model, a systematic experimental study with varying x in K 1−2x Co 1+x Fe(CN) 6 is desired especially.…”

mentioning

confidence: 87%

Novel Mechanism of Photoinduced Reversible Phase Transitions in Molecule-Based Magnets

2001

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A novel microscopic mechanism of bi-directional structural changes is proposed for the photoinduced magnetic phase transition in Co-Fe Prussian blue analogues on the basis of ab initio quantum chemical cluster calculations. It is shown that the local potential energies of various spin states of Co are sensitive to the number of nearest neighbor Fe vacancies. As a result, the forward and backward structural changes are most readily initiated by excitation of different local regions by different photons. This mechanism suggests an effective strategy to realize photoinduced reversible phase transitions in a general system consisting of two local components. 78.90.+t,71.35.Lk, Repeatable switching-on and -off of magnetization by external stimuli such as light is one of the most fascinating phenomena with potential applications in next generation's information storage and processing. A bi-directional photo-induced magnetization was first discovered in a cobalt-iron Prussian blue analogue,Illumination of visible light (500 -700 nm) at low temperature induces a bulk magnetization (presumably, ferrimagnetism), which can be eliminated by illumination of near-IR light (∼1300 nm). In spite of various experimental and theoretical efforts [1,2,[4][5][6][7][8], the microscopic mechanism of the reversible magnetization is still not clear. In this Letter we report ab initio quantum chemical cluster calculations for the Co-Fe Prussian blue analogue, unveiling the microscopic mechanism of the bi-directional photo-induced local structural changes that trigger the phase transitions.The crystal of a Prussian blue analogue K 1−2x Co 1+x Fe(CN) 6 is composed of two metallic sites located on vertices of the cubic lattice and each surrounded by six cyano moieties, as shown in Fig. 1. The d-orbitals of transition metals split into t 2g and e g orbitals by the ligand field. In the case of x =0, there are vacancy sites with replacement of CN by H 2 O as shown in Fig. 1(b). Various fascinating phenomena including a room temperature magnet [9], electrochemically tunable magnets [10], transparent and colored magnetic thin films [11], and photo-induced magnetic dipole inversion [12] have been observed in such non-stoichiometric compounds. We will show that this non-stoichiometric aspect is essential for the reversible photo-induced magnetization.The low spin (LS) configuration of the ground nonmagnetic state and the high spin (HS) configuration of the meta-stable magnetic state of K 0.4 Co 1.3 Fe(CN) 6 · 5H 2 O are most likely Co III (dε 6 , S = 0)Fe II (dε 6 , S = 0) and Co II (dε 5 dγ 2 , S = 3/2)Fe III (dε 5 , S = 1/2), respectively [1,2]. These are depicted in Fig.2 as LS0 and HS0 states. Figure 2 schematically represents the most plausible elementary processes in the cycle of the photo-induced structural change. The LH0 and HS0 states are converted to the intermediate states LS1 and HS1, respectively, by photo-induced charge transfer (CT) between iron and cobalt atoms, and then to the final states HS0 and LS0 by intersystem crossing due t...

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confidence: 87%

Novel Mechanism of Photoinduced Reversible Phase Transitions in Molecule-Based Magnets

2001

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“…Recent optical pump-probe reflectivity measurements have evidenced the photoinduced change of electronic state, both for the I-to-N and for the N-to-I transformations, on the 100 ps time scale (Koshihara et al, 1999, Iwai et al, 2002, Okamoto et al, 2004, Tanimura 2004. These laser-induced states relax to their thermodynamical stable phases in less than 1 ms.…”

Section: Cooperative Effects Around Neutral-ionic Phase Transitionmentioning

confidence: 99%

State of the art and opportunities in probing photoinduced phase transitions in molecular materials by conventional and picosecond X-ray diffraction

Collet¹,

Cointe²,

Lorenc³

et al. 2008

Zeitschrift Für Kristallographie - Crystalline Materials

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Abstract. The optical control of the macroscopic physical properties (magnetic, optical . . .) of a material by laser irradiation is gaining interest through the emerging field of photoinduced phase transitions. Light-induced changes of the macroscopic state of a material involves subtle coupling between the electronic and structural degrees of freedom, which are essential to stabilize the photo-excited state, different in nature from the stable state. Therefore the new experimental field of photocrystallography plays a key role. It goes far beyond simple structural analysis under laser excitation. By playing on different physical parameters and developing the techniques and analysis, one can investigate new out of equilibrium physics through light-driven cooperative dynamics and transformations in materials. This paper is reviewing different aspects of the use of photocrystallography to investigate the nature, the mechanisms and the dynamics of photoinduced phase transitions for photo-steady or long-lived states, as well as transformations driven by an ultra-short light pulse. We also give a brief overview on recent advances in time-resolved crystallography with 100 ps resolution.

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“…Another intriguing point, detectable in many photoexcitation kinetic data, is the frequent observation of an incubation stage [27,28], an effect reminiscent of some solid-state first-order transitions (cooperative photoprocess? [29]). Such effects remain to be elucidated in the general frame of a photoexcitation process that has little sensitivity to environment effects.…”

Section: Optical Switchingmentioning

confidence: 99%

Examples of molecular switching in inorganic solids, due to temperature, light, pressure, and magnetic field

Varret

Bleuzen

Boukheddaden

et al. 2002

Pure and Applied Chemistry

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Photoinduced Cooperative Charge Transfer in Low-Dimensional Organic Crystals

Cited by 220 publications

References 29 publications

Novel Mechanism of Photoinduced Reversible Phase Transitions in Molecule-Based Magnets

Novel Mechanism of Photoinduced Reversible Phase Transitions in Molecule-Based Magnets

State of the art and opportunities in probing photoinduced phase transitions in molecular materials by conventional and picosecond X-ray diffraction

Examples of molecular switching in inorganic solids, due to temperature, light, pressure, and magnetic field

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