To develop an organic-inorganic hybrid photomagnet, we performed the intercalation of sulfonate-substituted spiropyran anions into layered cobalt hydroxides, obtaining the photoresponsive compound, Co(OH)1.84 (nSPSO3)0.16 · 0.8H2 O (CoLHSP; nSPSO3: 1′,3′,3′-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2′-indoline]-5′-sulfonate). After UV irradiation (313 nm), the optical and magnetic properties of CoLHSP clearly changed. A new band emerged in the absorption spectrum at 564 nm, corresponding to the π - π∗transition in the open form of nSPSO3. Moreover, the photoisomerization of nSPSO3 induced a new ferrimagnetic phase transition at 10 K in the temperature dependence of DC and AC magnetic susceptibilities in addition to the ferrimagnetic phase transition at 15 K for the unirradiated sample. Analyzing the magnetic measurements before and after UV irradiation, we estimated the phototransformation ratio of the magnetic phase in CoLHSP at approximately 40%.
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