【Nat.Chem.】突破Fe键限制！新低自旋锰开关自旋寿命超100万年，刷新光控磁性纪录#

a, A general scheme for LIESST using potential wells for the LS (green) and HS (blue) states displaced along the totally symmetric normal coordinate _Q_HL(a1) by Δ_Q_HL as well as of excited quartet states at higher energy. The term symbols in parentheses refer to a _d_5 electron configuration in octahedral symmetry with the respective t_2_g and e__g orbital occupation given in the boxes. ISC, ISC′ and ISC′′ denote (horizontal) intersystem crossing followed by (vertical) vibrational relaxation. Δ_E_0HL and _E_a,HL refer to the zero-point energy difference between the HS and LS states and the HS → LS energy barrier, respectively. b, An illustration of the inverse energy gap law for the HS → LS relaxation23,26,27: displacing the HS potential well (blue) vertically to larger Δ_E_0HL values (light blue) reduces barrier height (_E_a,HL) and width. c, An illustration of the present covalency concept: more covalent, that is, stronger M–L bonds, shift the HS potential well (blue) horizontally to larger displacements Δ_Q_HL (light blue), which leads to larger reorganization energies _λ_HL → _λ_HL′ and higher HS → LS barriers _E_a,HL → _E_a,HL′.#

a, The molecular structure of 1. b, The DFT-optimized geometry of LS-1, with selected computed bond lengths of LS-1 and HS-1 in parentheses (in angstroms). c, The molecular structure of one of the two independent cations of LS-1 in the asymmetric unit shown with thermal ellipsoids at the 50% probability level determined by SCXRD at 91 K and selected weighted average bond lengths of the two independent cations in the unit cell (in angstroms). Counter ions and hydrogen atoms are omitted. The weighted average bond lengths of the light-induced HS-1 structure obtained from SCXRD at 91 K under irradiation with 560 nm are shown in parentheses. d. UV–visible absorption spectrum of 1 in MeCN at 293 K (filled green spectrum) with TDDFT-calculated oscillator strengths (black, shifted by 0.40 eV to lower energies42,43. B3LYP/Def2-TZVP/CPCM(acetonitrile)/D3BJ) and electron density difference maps of the bright 2MLCT(8), 2MLCT(11) and 2MLCT(16) Franck–Condon states showing electron density gain (blue) and depletion (red). An isosurface value of 0.003 a.u., hydrogen atoms omitted. A photograph of a solution of 1 in MeCN at 293 K and TA spectra of 1 in MeCN after excitation with 590 nm at 293 K. e, Kinetic traces obtained by TA spectroscopy at various temperatures (inset: _λ_obs(averaged) = 380–510 nm) and Arrhenius plot of the HS → LS recovery of 1 obtained from the variable-temperature TA spectra using excitation with _λ_exc = 590 nm in MeCN between 273 and 308 K.#

研究人员成功表征了目标配合物。如图2所示，衍射实验与理论计算证实其基态为低自旋。经光照激发后，配合物快速定量切换至高自旋态，表现出高达0.36电子伏特的活化能垒，使室温下的自旋寿命达到惊人的87微秒，远超传统铁体系。

团队深入探索了低温下的光开关行为。如图3所示，在130 K冷冻溶液中，光照使配合物由红变橙，自旋弛豫寿命达2.9小时；逐步升温测得其溶液中的光开关限制温度高达141 K，刷新了铁配合物保持二十多年的世界纪录。

a. UV–visibile absorption spectra of a solution of 1 at 130 K in 2-MeTHF/MeCN (29:1, v/v) obtained before and after steady-state irradiation with a 560-nm LED (2 min, blue) and absorption spectra obtained at various times after switching off the light source. The final spectrum is shown in green. The inset shows the recovery of the LS state observed at _λ_obs = 590 nm. The photographs show frozen solutions of 1 in 2-MeTHF/MeCN (29:1,v/v) after (HS-1, pale-orange–yellow) and before (LS-1, red) steady-state irradiation (2 min) with a 560-nm LED at 130 K. b, fs-TA spectra of 1 after excitation with 590 nm in MeCN at 293 K. c, An Arrhenius plot of 1 obtained from fs-TA spectra using excitation with 590 nm in MeCN between 233 and 293 K from temperature-dependent lifetimes _τ_4(T). d, The determination of _T_LIESST of HS-1 by UV–visibile–NIR absorption spectroscopy in 2-MeTHF/MeCN (29:1, v/v) solution. HS-1 was prepared from LS-1 at 95 K by irradiating at _λ_exc = 560 nm for 2 min, the temperature was increased with a rate of 0.3 K min−1 and re-formation of LS-1 was observed at _λ_obs = 590 nm.#

该效应在固体状态下同样表现优异。如图4所示，超导量子干涉仪检测证实，固体样品在10 K光照后展现出明显的自加速协同弛豫特征，固态限制温度达到112.5 K。得益于极高的自旋势垒，外推至77 K下的自旋寿命可超过100万年。基于此特性，研究人员进行了原理性展示。如图5所示，在77 K下利用掩模板空间可控光照，成功在纸片上写入并永久保存了二进制图案，且能通过白光或加热轻松擦除。

a, χ_m_T versus t plot of solid 1 at 10 K during irradiation with 590 nm (black circles, green line as guide to the eye). b, χ_m_T versus T plot (green) of solid 1 after irradiation at 10 K for 2 h, switching off the light source and warming with 0.4 K min−1, giving a _T_LIESST of 112.5 K.#

a, A photograph of a paper disc with LS-1 cooled to 77 K in a cryostat. b, Photographs of the paper after irradiation with a 560-nm LED through masks with the pattern ‘HS’ and ‘Mn’, respectively, at 77 K for approximately 2 min (spatially controlled HS-1 formation). c, A photograph of the paper after irradiation of the patterned disc with a white light torch to clear the pattern (full conversion to HS-1) (Supplementary Video 1). d, A photograph of the paper after warming of the patterned disc to clear the pattern (full conversion to LS-1). LS-1 appears brownish at low temperatures, which is a combination of slight band shifts and band narrowing at lower temperature (Supplementary Fig. 14), which leads to this colour perception by the human eye.#