Switching single chain magnet behavior via photoinduced bidirectional metal-to-metal charge transfer

The on/off-switching of single-chain magnetic behavior tuned through bidirectional light irradiation.


Table S1
Crystal data and structure refinements for complex 1.

Table S2
Selected bond lengths (Å) and angles ( o ) for complex 1 at 220 K.  (a) Temperature-dependent magnetic susceptibility of 1. (b) Isothermal magnetization of 1 at 1.8 K. (c) Temperature dependence of the in-phase and out-of-phase components of ac magnetic susceptibility in a zero dc field at various ac frequencies and with a 3.5 Oe ac field.

Fig. S5
Isothermal magnetization of 1 before irradiation, after irradiated at 808 nm and the metastable state irradiated at 532 nm at 1.8 K.

Fig. S6
Temperature dependence of the in-phase and out-of-phase components of ac magnetic susceptibility after irradiation at 808 nm (a) and 532 nm (b) in a zero dc field at various ac frequencies and with a 3.5 Oe ac field.

Fig. S7
Arrhenius plots for the magnetic relaxation process of 1 after irradiation at 808 nm based on the peak values of χ′′.

Fig. S8
Cole-Cole diagram for 1 after irradiation at 808 nm at 2.7 K. The solid red line represents the best fit of the experimental results with a generalized Debye model.

Fig. S9
(a) Plot of ln(χ′T) versus 1/T for 1 after irradiation at 808 nm. (b) Plot of ln(χ′T) versus 1/T for the metastable HS * state of 1 after irradiation at 532 nm (χ′ is the in-phase component of the ac susceptibility measured in zero dc field at 1 Hz).

Fig. S10
(a) Plots of χT vs time for 1 irradiated under 532 nm at 10 K. (b) Temperature dependence of the in-phase and out-of-phase components of ac magnetic susceptibility of 1 in a zero dc field at various ac frequencies and with a 3.5 Oe ac field after irradiation at 532 nm .

Fig. S11
Temperature dependence of the in-phase and out-of-phase components of ac magnetic susceptibility after irradiation at 808 nm (a) and 532 nm (b) in a zero dc field at various ac frequencies and with a 3.5 Oe ac field in the third cycle. Corresponding Arrhenius plots were shown with parameters describing the relaxation kinetics of 1 in the high-temperature range (30-50 K) and low-temperature range (10-20 K).

Fig. S14
Solid state FT-IR spectra for 1 at 200 K.

Fig. S15
The IR spectra for 1 irradiated at 808 nm and the photo-reversibility upon irradiation at 532 nm at 10 K.

Materials
All chemical reagents were commercially available and used without further

Structure Determination and Refinement
The single-crystal XRD data for 1 were collected on a Bruker Smart APEX II Xdiffractometer equipped with graphite monochromated Mo-Kα radiation (λ = 0.71073 Å) using the SMART and SAINT programs at 220 K. Final unit cell parameters were based on all observed reflections from integration of all frame data. The structures were solved in the space group by direct method and refined by the full-matrix leastsquares using SHELXTL-97 fitting on F 2 . For all compounds, all non-hydrogen atoms were refined anisotropically. The hydrogen atoms of organic ligands were located geometrically and fixed isotropic thermal parameters.

IR and UV-Vis Spectra measurements
Infrared spectra were measured on KBr pellets samples using a Nicolet IS10 FT-IR spectrometer equipped with a liquid helium type cryostat (Optistat CF 2 ). For infrared spectra after irradiation, the sample was continuously irradiated via a flexible optical fiber guided laser diode pumped Nd:YAG laser (λ = 808 nm, 39 mW/cm 2 ) and Nd:YAG laser ( = 532 nm， 10 mW/cm 2 ) at 10 K. Solid state UV-Vis absorption spectra were recorded on a HITACHIU-4100 UV-Vis spectrophotometer.

Magnetic and Photomagnetic Studies
Magnetic measurements were performed on a Quantum Design SQUID (MPMSXL-7) magnetometer with the polycrystalline samples. To prevent the loss of uncoordinated solvents, the fresh sample was loaded directly into the sample chamber at 110K (He atmosphere) and frozen before purging under vacuum. Variable-temperature magnetic measurements of the heating mode ware carried out from 2 K to 300 K. Data were corrected for the diamagnetic contribution calculated from Pascal constants.
Photomagnetic measurements were carried out with the same instrument but by using a sample equipped with an optical fiber. The powder sample of 1 was deposited on a commercial adhesive tape and placed on the edge of the optical fiber. The photoirradiation was performed with a laser diode pumped Nd:YAG lasers (λ = 808 nm, 39 mW/cm 2 ; λ = 532 nm, 10 mW/cm 2 ; λ = 473 nm, 10 mW/cm 2 ; λ = 405 nm, 5 mW/cm 2 ) and Nd: YVO4 laser (λ = 671 nm, 12 mW/cm 2 ). The temperature-dependent magnetization was measured both before and after irradiation in the range of 1.8-120 K. The difference in the magnetization before and after irradiation was extracted by subtracting the magnetization value before irradiation from that after irradiation.

Table S1
Crystal data and structure refinements for complex 1.

Fig. S5
Isothermal magnetization of 1 before irradiation, after irradiated at 808 nm and the metastable state irradiated at 532 nm at 1.8 K.

Fig. S6
Temperature dependence of the in-phase and out-of-phase components of ac magnetic susceptibility of 1 after irradiation at 808 nm (a) and 532 nm (b) in a zero dc field at various ac frequencies and with a 3.5 Oe ac field. and low-temperature range (10-20 K).
Relaxation of the photoinduced metastable state was monitored at different temperatures to probe the stability of the photoinduced phases. The decay of magnetization was normalized to the photoinduced fraction  and fitted to a stretched exponential law: where  represents the relaxation time of the system at temperature T and  represents the factor of time-evolving magnetic interactions during the decay owing to different magnetic interaction topologies in the high-and low-temperature phases (Fig. S12a). The obtained relaxation time  was fitted to an Arrhenius relationship ((T) =  0 exp(E/(k B T)), where  0 and E/k B represent the pre-exponential factor and the energy barrier, respectively. Two distinct dependencies of  on temperature were observed (Fig. S12b). In the low-temperature (10-20 K) region,  was less dependent on temperature. A best fitting procedure gave E/k B = 1.9(0.4) cm 1 and  0 = 2.010 5 s. In the high-temperature range (30-50 K), the relaxation time  was strongly dependent on temperature, giving an energy barrier E/k B = 157.5(25.7) cm 1 and  0 = 568.7 s. The IR spectra for 1 irradiated at 808 nm and the photo-reversibility upon irradiation at 532 nm at 10 K.