Ultrafast Photoswitching in a Copper‐Nitroxide‐Based Molecular Magnet

Abstract

Molecular compounds with photoswitchable magnetic properties have been intensively investigated over the last decades due to their prospective applications in nanoelectronics, sensing and magnetic data storage. The family of copper-nitroxide-based molecular magnets represents a new promising type of photoswitchable compounds. We report the first study of these appealing systems using femtosecond optical spectroscopy. We unveil the mechanism of ultrafast (<50 fs) spin state photoswitching and establish its principal differences compared to other photoswitchable magnets. On this basis, we propose potential advantages of copper-nitroxide-based molecular magnets for the future design of ultrafast magnetic materials.

Light‐Induced Spin Transitions in Copper‐Nitroxide‐Based Switchable Molecular Magnets: Insights from Periodic DFT+U Calculations

“…[20] with permission from the PCCP Owner Societies. l = 500 nm observed only at low temperature (SS state), and tentatively assigned to ac harget ransfer band (metal-toligand [13] or ligand-to-metal). [13,14] Af urtherf eature is the displacemento ft he structureb and centered at~650 nm, associated with the nitroxide radicals, to ah igher energy.…”

“…[1,6] Recently,afamily of switchable compoundsw ith SCO-like behavior and LIESST-like phenomena, based on Cu II and nitronyl nitroxide (NIT) ligands have been reported. [7][8][9][10][11][12][13][14] These compounds of formula Cu(hfac) 2 L R consist of heterospinp olymerchain complexes of Cu II hexafluoroacetylacetonato (hfac) with stable pyrazole-substituted nitronyl nitroxides, L R ,w ith R = Me, Et, Pr, iPr,B u. Twod ifferent motifs of the polymer chains can be obtained ( Figure 1): ah ead-to-tail motif leading to the formation of two-spin Cu II -nitroxide clusters, and ah ead-to-head motif,r esulting in alternating one-spin Cu II and three-spin NIT-Cu II -NIT clusters (spin triads).…”

“…[21] The process has been also analyzed by femtosecondo ptical spectroscopyf or aC u(hfac) 2 L Pr complex. [13] Figure3 shows the UV/ Vis absorption spectra of the WS and SS states of Cu(hfac) 2 L Pr , which are dominated by the nitronyl nitroxide bandsi nt he l = 450-700 nm region. [13,14] SimilarU V/Vis spectra have been reported for the relatedC u(hfac) 2 L Me and Cu(hfac) 2 L Et-CP complexes (whereL Et-CP = 2-(1-ethylpyrazol-4-yl)-4,5-bis(spirocyclopentane)-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl).…”

“…[13] Figure3 shows the UV/ Vis absorption spectra of the WS and SS states of Cu(hfac) 2 L Pr , which are dominated by the nitronyl nitroxide bandsi nt he l = 450-700 nm region. [13,14] SimilarU V/Vis spectra have been reported for the relatedC u(hfac) 2 L Me and Cu(hfac) 2 L Et-CP complexes (whereL Et-CP = 2-(1-ethylpyrazol-4-yl)-4,5-bis(spirocyclopentane)-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl). [14] The most significant differenceb etween both states is as trong band at 6 and CuO 4 N 2 octahedron, respectively.…”

Spatial distribution of phases during gradual magnetostructural transitions in copper(ii)–nitroxide based molecular magnets

“…8,9 Although the spin state of copper(II) cannot be changed, the total spin state of exchange-coupled copper(II)-nitroxide clusters can be changed. 8,9,[21][22][23][24][25][26][27][28][29][30][31][32][33][34] The temperature dependence of the effective magnetic moment (μ eff (T )) strongly varies from compound to compound: abrupt or gradual transitions in one to three steps of different amplitudes may be observed. They are often called "breathing crystals" due to the large and reversible changes in unit cell volume occurring during magnetostructural transitions.…”