Photoinduced Significant Magnetization Enhancement in a Viologen-Based Photochromic Compound

Large enhancement of magnetization at room temperature (RT) is highly desirable for real application of photomagnets, but only one known example shows remarkable enhancement of magnetization at room temperature (>30%). This work has successfully obtained a viologen-based complex which exhibited room temperature photochromism and photomagnetism and realized remarkable enhancement of magnetization at room temperature by photoinduced electron transfer. The present viologen-based complex exhibits the second largest magnetization increasing amplitude of 31.1% at room temperature among electron transfer photochromic systems

Photochromism and Photomagnetism of a 3d–4f Hexacyanoferrate at Room Temperature

Polycyanometallate compounds with both photochromism and photomagnetism have appealing applications in optical switches and memories, but such optical behaviors were essentially restricted to the cryogenic temperature. We realized, for the first time, the photochromism and photomagnetism of 3d–4f hexacyanoferrates at room temperature (RT) in [Eu^III(18C6)­(H₂O)₃]­Fe^III(CN)₆·2H₂O (18C6 = 18-crown-6). Photoinduced electron transfer (PET) from crown to Fe­(III) yields long-lived charge-separated species at RT in air in the solid state and also weakens the magnetic susceptibility significantly. The PET mechanism and changing trend of photomagnetism differ significantly from those reported for known 3d–4f hexacyanoferrates. This work not only develops a new type of inorganic–organic hybrid photochromic material but opens a new avenue for RT photomagnetic polycyanometallate compounds

Influence of Supramolecular Interactions on Electron-Transfer Photochromism of the Crystalline Adducts of 4,4′-Bipyridine and Carboxylic Acids

We have studied the electron-transfer photochromism of the crystalline adducts of 4,4′-bipyridine (Bpy) and carboxylic acids and revealed the key structural parameters that decide whether the photochromism can happen for the first time. Experimental and theoretical analyses on nine known examples showed that the hydrogen bonds, instead of π–π stacking interactions, are the defining factor to the photochromism. Only the presence of N–H···O hydrogen bonds can fulfill the electron transfer from the carboxylate group to the Bpy part, although both the N···O separations of O–H···N and N–H···O hydrogen bonds are suitable for the so-called through-space electron transfer. These results can not only help to screen out the photochromic species from the known hundreds of Bpy–carboxylic acid adducts deposited in the Cambridge Crystallographic Data Centre (CCDC) database but also guide the design and syntheses of new adducts using diverse <i>N</i>-heterocyclic aromatic molecules and carboxylic acids

Reversible Single-Crystal-to-Single-Crystal Transformation and Magnetic Change of Nonporous Copper(II) Complexes by the Chemisorption/Desorption of HCl and H₂O

Vapor-responsive magnetic materials are highly promising for applications as chemical switches or sensors. Compared with porous materials, nonporous species benefit in overcoming the intrinsic conflict between magnetic exchange and porosity but usually suffer from the powdering of single crystals, which hinders the understanding of the structural nature of vapor response and magnetic switch. Single-crystal-to-single-crystal (SCSC) transformation of nonporous compounds through the desorption/absorption of gaseous HCl is unprecedented. Reported here is a discrete nonporous copper­(II) complex, (H₃O)­[K­(15-crown-5)₂]­[CuCl₄], that exhibits reversible SCSC transformation and magnetic change by the chemisorption/desorption of HCl and H₂O. Significant changes in the coordination number (4 ↔ 3), space group (<i>P</i>1̅ ↔ <i>P</i>2₁/<i>c</i>), color (green ↔ red), and magnetic behavior (antiferromagnetic ↔ paramagnetic) were found during the SCSC transformation