Room-temperature thermally induced relaxation effect in a two-dimensional cyano-bridged Cu-Mo bimetal assembly and thermodynamic analysis of the relaxation process

We observed a photo-switching effect in [CuII(1,4,8,11-tetraazacyclodecane)]2[MoIV(CN)8]·10H2O by irradiation with 410-nm light around room temperature using infrared spectroscopy. This photo-switching is caused by the photo-induced charge transfer from MoIV to CuII. The photo-induced phase thermally relaxed to the initial phase with a half-life time of 2.7 × 101, 6.9 ×101, and 1.7 × 102 s at 293, 283, and 273 K, respectively. The relaxation process was analyzedusing Hauser's equation, k =k0exp[−(Ea +Ea*γ) /kBT], where k is the rate constant of relaxation, k0 is the frequency factor, Eais the activation energy,Ea* is the additional activation energy due to the cooperativity,and γ is the fraction of the photo-induced phase. k0, Ea, and Ea* were evaluated as 1.28 × 107 ± 2.6 s−1, 4002 ± 188 cm−1, and 546 ± 318 cm−1, respectively. The value of Ea is much larger than that of the relaxation process for the typical light-induced spin crossover effect (Ea ≈1000 cm−1). Room-temperature photo-switching is an important issue in the field of optical functional materials. The present system is useful for the demonstration of high-temperature photo-switching material.