Electrochromic Thin Films of the V-Cr Prussian Blue Analogue Molecular Magnet

Abstract

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.

Electrochromic bilayers of Prussian blue and its Cr analogue

“…In order to fit all the required electrodes for the spectroelectrochemical measurements into the cuvette, the SCE reference and counter electrode were replaced with Pt wire electrodes. A previous investigation 22 of this arrangement of electrodes showed that the use of the pseudo-reference results in a shift of less than 0.02 V with respect to the SCE arrangement. Cyclic voltammograms were carried out on each of the layers individually and the bilayer structure in order to determine switching potentials to be used during the spectroelectrochemistry.…”

Observation of excited state absorption in the V-Cr Prussian blue analogue

“…[31] and references therein). Inspired by our recent spectroelectrochemical study on thin films of the V-Cr PBA [16], we have in this letter investigated if a similar approach would be feasible. In the spectroelectrochemical study, we found that a new optical absorption peak arises at ca.…”

“…The V-Cr PBA also displays interesting proton conductive [13], photomagnetic [14] and electrochromic [15,16] properties. There have been few ultrafast studies to date on PBAs in general [17][18][19][20][21][22] to probe the initial fs−ps dynamics after photoexcitation.…”

Color combination of polysiloxane polymer by introducing two different triphenylamine based pendent groups for electrochromism

“…Electrochromism lies in the variation of the optical properties consisting of the color, transparency, etc., when subjected to the electric charge . Giving the credit to the properties of high color contrast and low voltage consumption, electrochromic materials are potential for applications such as smart windows, rear‐view mirrors, information displays, electronic papers, and military camouflage . WO 3 was first reported as electrochromic material by Deb in 1969 .…”

“…[1][2][3][4] Giving the credit to the properties of high color contrast and low voltage consumption, electrochromic materials are potential for applications such as smart windows, rear-view mirrors, information displays, electronic papers, and military camouflage. [5][6][7][8] WO 3 was first reported as electrochromic material by Deb in 1969. 9 After that, various electrochromic materials including metal oxides, coordination complexes, small organic molecule, side-chain-substituted polymers, or main-chain fully conjugated polymers were reported.…”