One Shot Laser Pulse Induced Reversible Spin Transition in the Spin‐Crossover Complex [Fe(C₄H₄N₂){Pt(CN)₄}] at Room Temperature

Abstract

The use of light is one of the most promising ways to reversibly control various physical properties of organic and metal-organic compounds and opens up the possibility for the generation of new information storage devices. [1,2] Among these materials, iron(ii) spin-crossover complexes are particularly interesting as they are known to exhibit a light-induced low-spin (LS) to high-spin (HS) transition.[3] However, this light-induced excited spin state trapping (LIESST) phenomenon is only efficient at cryogenic temperatures (typically below 50 K) because at higher temperatures the photoinduced HS state relaxes rapidly to the ground state. This is a serious limitation for the development of optical switches based on spin-crossover materials.A possible approach to overcome this problem consists of working within the thermal hysteresis loop, in which the metastable HS or LS states have "infinite" lifetimes.[4] Such hysteresis phenomena have been found in many spin-crossover solids and can be related to long-range elastic interactions between the spin-state-changing molecules.[5] It should be emphasized that the hysteresis loop can be finetuned by chemical methods to situate it around room temperature.[6] The first light-induced LS!HS transition in the hysteresis region was recently observed by means of optical reflectivity when an 8-ns laser pulse was applied at 170 K to [Fe(pm-bia) 2 (NCS) 2 ] (pm-bia = N-2'-pyridylmethylene-4-aminobiphenyl), but the reverse phenomenon could not be detected.[2a] Herein, we report spectroscopic evidence for a bi-directional, light-induced spin transition at room temperature in [Fe(pyrazine){Pt(CN) 4 }] (Figure 1) by applying a one-shot laser pulse of irradiation.The synthesis of a hydrated form of the above-mentioned compound has been reported elsewhere.[7] Subsequent research has demonstrated that the spin-crossover behavior of this hydrated form ([Fe(pyrazine){Pt(CN) 4 }]·n H 2 O; n % 2-3) depends dramatically on the water content. Thermogravimetric analysis revealed that heating the sample at 420 K for 30 minutes is necessary to remove the water of crystallization. The dehydrated form [Fe(pyrazine){Pt(CN) 4 }] exhibits "improved" spin-crossover behavior in that the transition becomes complete and is centered at room temperature. Moreover, the hysteresis loop becomes wider, square-shaped, and reproducible over several cycles. This compound preserves its spin state (HS or LS) for several months if it is kept in a dry atmosphere at room temperature (295 K). Figure 2 shows the temperature dependence of the c M T value (c M is the molar magnetic susceptibility) for

Optical Data Storage in Photosensitive Glasses and Spin State Transition Compounds

“…One year after our work, it has been shown that different compounds can be photo-switched at room temperature using a single Nd:YAG Q-switched laser pulse (Bonhommeau et al, 2005). However, the details of the mechanisms giving rise to the switching of the spin state compound within the thermal hysteresis was difficult to evidence (Fouché et al, 2009).…”

Single Laser Shot Spin State Switching of {FeII(pz)[Pt(CN)4]} Inside Thermal Hysteresis Studied by X-ray Diffraction

“…There are many SCO systems in the literature undergoing a first-order phase transition between LS and HS states and describing a thermal hysteresis. Some reports have demonstrated that the photoexcitation of the LS state inside the thermal hysteresis can generate the HS phase [7,8,9] 4 )]} (pz=pyrazine) compound studied here was evidenced by Bousseksou et al by Raman, optical spectroscopy and magnetic measurements [9][10][11][12]. In crystals, the photoinduced out-of-equilibrium dynamics initiated by a laser pulse involves several steps [13][14][15][16][17][18].…”

Control of Spin-Crossover Phenomena in One-Dimensional Triazole-Coordinated Iron(II) Complexes by Means of Functional Counter Ions

“…Therefore, another approach has been eagerly anticipated. Recently, the photoinduced SCO phenomenon has been demonstrated for [Fe(II)(pz){Pt(CN) 4 }] (pz is pyrazine) [58] and [Fe(II)(NH 2 -trz) 3 ](Br) 2 ·3H 2 O by photoirradiation within the thermal hysteresis loop of the SCO transition [59]. Such a strategy is one of the possible approaches to control the spin states in SCO compounds at room temperature.…”

“…In the [Fe(II)(pz){Pt(CN) 4 }] complex, where thermal SCO transitions occur at Tc↑ = 284 K and Tc↓ = 308 K with a hysteresis width of 24 K, light-induced spin transition at room temperature was achieved by applying one-shot laser-pulsed irradiation [58]. The photoinduced spin conversion was confirmed by investigating Raman bands at 650 and 682 cm −1 assigned to the in-plane bending mode of the pyrazine ring for the HS and LS states, respectively.…”