Photoswitchable 11 nm CsCoFe Prussian Blue Analogue Nanocrystals with High Relaxation Temperature

Abstract

Photo-switchable 11 nm nanocrystals of the coordination network Cs{Co[Fe(CN)6]} were obtained using a template-free method. The nanocrystals were recovered from the colloidal solutions as solid materials surrounded by cetyltrimethylammonium (CTA) cations or embedded in the organic polymer polyvinylpyrrolidone (PVP). Complementary magnetic, spectroscopic and structural techniques, including EPR Spectroscopy, reveal a majority (≈70%) of the low spin and photoactive diamagnetic Co III Fe II pairs located in the core of the nanocrystals and a mixture of Co II Fe II and Co II Fe III species present mainly within the shell of the objects. While bulk compounds with similar vacancy concentration do not exhibit noticeable photoinduced charge transfer, the obersved photoactivity of the nanocrystals is ascribed to their nanometric size. The relaxation temperature of the photo-induced state shifts upwards by ≈ 55 K when PVP is replaced by CTA. This is ascribed to the larger rigidity of the dense CsCoFe_CTA material whose metastable state is lower than for CsCoFe_PVP leading to a larger relaxation energy barrier and, therefore, to higher relaxation temperature.

Collective Magnetic Behavior of 11 nm Photo-Switchable CsCoFe Prussian Blue Analogue Nanocrystals: Effect of Dilution and Light Intensity

“…A Transmission Electron Microscopy (Jeol 1400, Jeol, Tokyo, Japan) image of the CTA materials showed objects with an average size close to 11 nm (Figure 1). The X-ray power diffraction (Panalytical X-Pert Pro MPD, Malvern Panalytical, Malvern, UK) diagram of the same material was consistent with face centered cubic structure as expected for Prussian blue analogues with a cell parameter a = 10.01 Å (Figure 1) [8]. The infrared spectrum (Perkin Elmer Spectrum 100, PerkinElmer Inc., Norwalk, Connecticut, USA) (Figure 1) in the 2300-1900 cm −1 regions showed the asymmetric vibration mode of the cyanide at 2115 cm −1 characteristics of cyanide bridge corresponding to a mixture of Fe(II)-CN-Co(III) and Fe(II)-CN-Co(III) sequences [8].…”

“…The X-ray power diffraction (Panalytical X-Pert Pro MPD, Malvern Panalytical, Malvern, UK) diagram of the same material was consistent with face centered cubic structure as expected for Prussian blue analogues with a cell parameter a = 10.01 Å (Figure 1) [8]. The infrared spectrum (Perkin Elmer Spectrum 100, PerkinElmer Inc., Norwalk, Connecticut, USA) (Figure 1) in the 2300-1900 cm −1 regions showed the asymmetric vibration mode of the cyanide at 2115 cm −1 characteristics of cyanide bridge corresponding to a mixture of Fe(II)-CN-Co(III) and Fe(II)-CN-Co(III) sequences [8]. Combined powder X-ray diffraction, magnetic, Electron Paramagnetic Resonance, and X-ray photoelectron spectroscopy studies are consistent with the presence at room temperature of the different phases Co II Fe II , Co II Fe III , and Co III Fe II , the latter contributing to 70% of the overall concentration of each nanocrystal [8].…”

“…The preparation and full characterization of the nanocrystals were recently reported [8]. The nanocrystals were prepared in water as a stable colloidal solution then recovered by CTA + and by PVP to give two samples, namely CsCoFe_CTA and CsCoFe_PVP.…”

“…Magnetochemistry 2021, 7, 99 2 of 12 Recently we reported [8], the photoswitching behavior of nanocrystals in the sub-15 nm size containing a large concentration of Cs and almost no vacancies i.e., (CTA) 0.4 [Cs 0.7 -Co{Fe(CN) 6 } 0.9 ]•H 2 O that have a majority of the diamagnetic phase at room temperature and present a light induced switching to the magnetic state at low temperatures. The photoswitching behavior was studied when the particles were embedded in CetylTrimethy-lAmmonium (CTA + ) which serves as counter-cation for the nanocrystals and for the objects surrounded by the organic polymer polyvinylpyrrolidone (PVP).…”

Ultrafast photoinduced dynamics in Prussian blue analogues

“…121 The sample studied was a colloidal solution of Cs 0.7 Co[Fe(CN) 6 ] 0.9 nanoparticles with 11 nm diameter in the LT phase at room temperature. 134 This was a ground-breaking study in many ways because it determined the nature of the transition at 540 nm, for which there was previously some debate, 119,120 and could even show the sequence of the initial states involved in the CT and spin transitions. The time-resolved data at the Co K-edge had to be fitted with three decay constants of 50, 200 and 450 fs (Fig.…”