Controllable quantum systems are under active investigation for quantum computing, secure information processing, and nonvolatile memory. The optical manipulation of spin quantum states provides an important strategy for quantum control with both temporal and spatial resolution. Challenges in increasing the lifetime of photoinduced magnetic states at T > 200 K have hindered progress toward utilizing photomagnetic materials in quantum device architectures. Here we demonstrate reversible light-induced magnetization switching in an organic thin film at device operating temperatures of 300−330 K. By utilizing photochromic ligands that undergo structural changes in the solid state, the changes in ligand field associated with photoisomerization modulate the ligand field and in turn the oxidation and spin state of a bound metal center. Green light irradiation (λ exc = 550 nm) of a spirooxazine cobalt−dioxolene complex induces photoisomerization of the ligand that in turn triggers a reversible intramolecular charge-transfer coupled spin-transition process at the cobalt center. The generation of photomagnetic states through conversion between a low-spin Co(III)−semiquinone doublet and a high-spin Co(II)−bis-semiquinone sextet state has been demonstrated in both solution and the solid state and is described as a photoisomerization-induced spin−charge excited state (PISCES) process. The high transition temperature (325 K) and long-lived photoinduced state (τ = 10 s at 300 K) are dictated by the photochromic ligand. Theory provides effective modeling of the phenomenon and long-term strategies to further modulate the lifetimes of photomagnetic states for quantum information technologies at the single molecule level.

The new tritopic triaminoguanidine-based ligand 1,2,3-tris[(pyridine-2-ylmethylidene)amino]guanidine (Hpytag) was synthesized. The reaction of a mixture of cobalt(II) chloride and cobalt(II) perchlorate with the ligand Hpytag in pyridine solution leads to the formation of the trinuclear cobalt(II) complex [Co(pytag)(py)Cl]ClO. Three octahedrally coordinated high-spin cobalt(II) ions are linked through the bridging triaminoguanidine backbone of the ligand leading to an almost equilateral triangular arrangement. The magnetic properties of the complex were investigated by magnetic measurements, variable-temperature, variable-field magnetic circular dichroism (MCD) spectroscopy, and density functional theory as well as ab initio calculations. A rather strong antiferromagnetic exchange interaction between the cobalt(II) centers of ca. -12 cm is determined together with a strong local anisotropy. The single-ion anisotropy of all three cobalt(II) centers is found to be easy-plane, which coincides with the tritopic ligand plane. MCD measurements and theoretical investigations demonstrate the presence of rhombic distortion of the local Co surrounding.

We present the synthesis and crystal structure of the trinuclear copper complex [Cu3(saltag)(bpy)3]ClO4·3DMF [H5saltag = tris(2-hydroxybenzylidene)triaminoguanidine; bpy = 2,2'-bipyridine]. The complex crystallizes in the trigonal space group R3̅, with all copper ions being crystallographically equivalent. Analysis of the temperature dependence of the magnetic susceptibility shows that the triaminoguanidine ligand mediates very strong antiferromagnetic interactions (JCuCu = -324 cm(-1)). Detailed analysis of the magnetic susceptibility and magnetization data as well as X-band electron spin resonance spectra, all recorded on both powdered samples and single crystals, show indications of neither antisymmetric exchange nor symmetry lowering, thus indicating only a very small splitting of the degenerate S = (1)/2 ground state. These findings are corroborated by density functional theory calculations, which explain both the strong isotropic and negligible antisymmetric exchange interactions.

Chemists usually synthesize molecules using stochastic bond-forming collisions of the reactant molecules in solution. Nature follows a different strategy in biochemical synthesis. The majority of biochemical reactions are driven by machine-type protein complexes that bind and position the reactive molecules for selective transformations. Artificial "molecular assemblers" performing "mechanosynthesis" have been proposed as a new paradigm in chemistry and nanofabrication. Here we present a simple non-proteinogenic machine-type molecule which drives the endergonic condensation of vanadate to cyclic tetravanadate using light as the energy source. The system combines selective binding of the reactants, accurate positioning, and active release of the product. Hydrolysis of the product prevents inhibition of further cycles. Our prototypic system demonstrates the prerequisites that are needed to selectively drive an endergonic reaction using an external energy source.

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