Spin Crossover Meets Diarylethenes: Efficient Photoswitching of Magnetic Properties in Solution at Room Temperature

Abstract

A photoisomerizable diarylethene-derived ligand, phen*, has been successfully introduced into a spin-crossover iron(II) complex, [Fe(H2B(pz)2)2phen*] (1; pz =1-pyrazolyl). A ligand-based photocyclization (photocycloreversion) in 1 modifies the ligand field, which, in turn, results in a highly efficient paramagnetic high-spin → diamagnetic low-spin (low-spin → high-spin) transition at the coordinated Fe(II) ion. The reversible photoswitching of the spin states, and thus the associated magnetic properties, has been performed in solution at room temperature and has been directly monitored by measuring the magnetic susceptibility via the Evans method. The observed spin-state photoconversion in 1 exceeds 40%, which is the highest value for spin-crossover molecular switches in solution at room temperature reported to date. The photoexcited state is extraordinarily thermally stable, showing a half-time of about 18 days in solution at room temperature. Because of the outstanding photophysical properties of diarylethenes, including single-crystalline photochromism, molecular switch 1 may offer a promising platform for controlling the magnetic properties in the solid state and ultimately at the single-molecule level with light at room temperature.

Switching Magnetic Properties by a Mechanical Motion

“…Recently Khusniyarov et al have used a phenanthroline ligand functionalized by a photochromic diarylethene moiety in a bis(pyrazolyl)borate Fe(II) complex ( Figure 6). Under UV-irradiation, the open HS form is reversibly converted (about 40%) to a LS closed form [49,50]. In parallel, Oshio et al studied similar compounds and showed bidirectional spin-state switching by LIESST and reverse-LIESST in the solid state and in butyronitrile solution [51].…”

Spin-state dynamics of a photochromic iron(II) complex and its immobilization on oxide surfaces via phenol anchors

“…An interesting recent access to trapped spin states relies on light-driven isomerization within the ligand sphere. Here the spin state is altered via variation of the ligand-field strength (light-driven ligand-induced spin change, LD-LISC [9,10]) or variation of the ligand-field symmetry (light-driven coordination-induced spin-state switching, LD-CISSS [11,12]). Most commonly, however, it is only at cryogenic temperatures,…”

Synthesis and Photochromism Studies of 1-[2-methyl-5-(2-pyridyl)-3-thienyl]-2-[2-methyl-5-(4-bromomethylphenyl)-3-thienyl] Perfluorocyclopentene

“…For example, diarylethenes bearing thiophene moiety and six-membered pyridine unit exhibited good photochromism both in solution and in the crystalline phase by permitting the pyridine unit to participate in the photoinduced cyclization reaction [5][6][7]. What's more, the bearing of heteroatom of diarylethenes can dramatically change photochromism properties and expand multiple responsive switching systems [8,9]. Herein, we have designed and synthesized a new diarylethene bearing thiophene moiety and pyridine unit, namely 1-[2-methyl-5-(2-pyridyl-3thienyl]-2-[2-methyl-5-(4-bromomethylphenyl)-3-thienyl]perfluorocyclopentene.…”