Control of the Speed of a Light-Induced Spin Transition through Mesoscale Core–Shell Architecture

Abstract

The rate of the light-induced spin transition in a coordination polymer network solid dramatically increases when included as the core in mesoscale core-shell particles. A series of photomagnetic coordination polymer core-shell heterostructures, based on the light-switchable Rb Co[Fe(CN)] · mHO (RbCoFe-PBA) as core with the isostructural K Ni[Cr(CN)] · nHO (KNiCr-PBA) as shell, are studied using temperature-dependent powder X-ray diffraction and SQUID magnetometry. The core RbCoFe-PBA exhibits a charge transfer-induced spin transition (CTIST), which can be thermally and optically induced. When coupled to the shell, the rate of the optically induced transition from low spin to high spin increases. Isothermal relaxation from the optically induced high spin state of the core back to the low spin state and activation energies associated with the transition between these states were measured. The presence of a shell decreases the activation energy, which is associated with the elastic properties of the core. Numerical simulations using an electro-elastic model for the spin transition in core-shell particles supports the findings, demonstrating how coupling of the core to the shell changes the elastic properties of the system. The ability to tune the rate of optically induced magnetic and structural phase transitions through control of mesoscale architecture presents a new approach to the development of photoswitchable materials with tailored properties.

Molecular Spin Crossover Materials: Review of the Lattice Dynamical Properties

“…Consequently, the HS‐LS phase stability as well as the cooperativity of the SCO are impacted. This effect was clearly demonstrated in the case of quasi‐epitaxial core–shell nanoparticles of switchable Prussian blue analogue (PBA) compounds …”

“…As an example, Figure shows X‐ray diffraction patterns recorded both on uncoated and core–shell nanoparticles of a RbCoFe PBA compound displaying a charge transfer induced spin transition (CTIST) upon variation of temperature . The striking observation is the vanishing of the first‐order nature of the phase transition in particles coated by the KNiCr PBA shell.…”

“…The presence of the shell transforms the initially discontinuous (first‐order) transition in a gradual conversion. Reproduced with permission . Copyright 2018, American Chemical Society.…”

Design of Bistable Gold@Spin‐Crossover Core–Shell Nanoparticles Showing Large Electrical Responses for the Spin Switching

“…Here the chemical design of core–shell nanoparticles (NPs) formed by a metallic Au core and a SCO shell is undertaken. Despite the extensive works performed on core–shell NPs, nanostructures formed by a metallic core and a molecular SCO shell are unprecedented. In addition, as compared to previous examples that contain simple SCO entities deposited or contacted to gold surfaces/electrodes, the core–shell configuration reported here is expected to combine in a single nanostructure the metallic behavior of the core with the insulating behavior of the SCO shell.…”

Design of Bistable Gold@Spin-Crossover Core-Shell Nanoparticles Showing Large Electrical Responses for the Spin Switching

“…Our strategy to reach this goal consists of designing core-shell nanoparticles (NPs) formed by a metallic Au core and a SCO shell. Despite the extensive works performed on core-shell NPs, [10][11][12] nanostructures formed by a metallic core and a molecular SCO shell are unprecedented. In addition, as compared to previous examples that combine SCO entities and conducting metals, [13][14][15][16][17] the core-shell configuration is expected to confront the insulating SCO behaviour.…”