This paper describes spectroelectrochemical measurements of thin films of the V II/III -Cr III Prussian blue analogue (V-Cr PBA). We show that we can electrically control the optical properties of this room-temperature molecule-based magnet and reversibly switch the colour of the films from blue to black upon reduction. The cyclic voltammogram of the films showed a weak wave at −0.85 V and a stronger wave at −1.22 V. The spectroelectrochemical measurement in KCl indicate that the wave at −0.85 V is related to the reduction of V(III) to V(II) because of a shift in the absorption band associated with the metal-to-metal charge-transfer band.The wave at −1.22 V occurred simultaneously with the growth of a new absorption feature at 465 nm and is attributed to the reduction of [Cr III (CN)6] 3sites to [Cr II (CN)6] 4-. We have assigned the change to the optical spectrum occurring at 465 nm after electrochemical reduction to a red-shift of a metal-to-ligand charge-transfer (MLCT) transition from Cr 2+ to empty π* ligand orbitals. The electrochromic coloration efficiency associated with switching from blue to black colour was found to be = −25.2 ± 0.2 cm 2 C −1 with a switching time of 6.6 s at −1.3 V. These findings demonstrate the possibility to electrically control the optical properties of a room-temperature molecular magnet.

The distinct optical absorption spectra of the two layers allowed spectroelectrochemical measurements to probe the electrochemical activity of the individual layers during the switching of the Prussian blue layer.We found that for producing layers of equal optical density, the thickness of the layers had to be different due to a difference in oscillator strength for the metal-to-metal charge-transfer transition. The films used here had a thickness of 300 AE 70 nm and 30 AE 15 nm for the FeCr and FeFe sub-layers, respectively.The colouration efficiency was found to be 147.8 AE 0.8 cm 2 C À1 for the multilayered film. These resultsshow that it is possible to obtain bilayers of Prussian blues that, with a unique optical spectral fingerprint of each sub-layer, retain the electrochromic functionality and therefore enable layer-sensitive studies of charge-transfer processes in thin film heterostructures of multifunctional materials.

We present femtosecond transient transmission measurements of thin films of the V II/III -Cr III Prussian blue analogue (V-Cr PBA) in the spectral range 330−675nm after exciting the ligand-to-metal charge-transfer transition (LMCT) at 400nm. A global analysis including three decay-times of τ1=230fs, τ2=1.38ps and τ3>>2ns could satisfactory describe the data. We observed an excited state absorption (ESA) at 345nm, which was attributed to a chargetransfer transition from the 2 E state on the Cr ions after fast intersystem crossing from the quartet manifold. An additional weak and short-lived ESA at 455nm was also observed and was tentatively attributed to the initially populated 4 LMCT state.

The long-term future of information storage requires the use of sustainable nanomaterials in architectures operating at high frequencies. Interfaces can play a key role in this pursuit via emergent functionalities that break out from conventional operation methods. Here, spin-filtering effects and photocurrents are combined at metal-molecular-oxide junctions in a hybrid magnetocapacitive memory. Light exposure of metal-fullerene-metal oxide devices results in spin-polarized charge trapping and the formation of a magnetic interface. Because the magnetism is generated by a photocurrent, the writing time is determined by exciton formation and splitting, electron hopping, and spin-dependent trapping. Transient absorption spectroscopy measurements show changes in the electronic states as a function of the magnetic history of the device within picoseconds of the optical pumping. The stored information is read using time-resolved scanning magneto optic Kerr effect measurements during microwave irradiation. The emergence of a magnetic interface in the picosecond timescale opens new paths of research to design hybrid magneto-optic structures operating at high frequencies for sensing, computing, and information storage.

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