When an aqueous electrolyte is frozen, anions and cations are distributed between liquid and ice phases in different fashions. This partition imbalance is relaxed by the transfer of H + and OH − to each phase, resulting in the acidification of the liquid phase when the cation is better distributed in the ice phase than the anion and in the basification in the opposite situation. In this work, a pH change in the liquid phase has been precisely evaluated by fluorescence ratiometry with pyranine as the pH probe. For frozen alkali chlorides (LiCl, NaCl, and KCl), the liquid phase is always basified by freezing due to the preferential partition of Cl − over the alkali metal cations. Changes in pH are quantitatively analyzed by a partition model, in which the distribution of an ion between the liquid and ice phases is determined by the partition coefficient. Since the concentration of a salt (i.e., ions) in the liquid phase in contact with ice becomes higher as freezing proceeds, the concentration of the ions in the ice phase is higher near the interface with the liquid phase and decreases toward the interior of ice. When the temperature of a frozen electrolyte increases, the ionic imbalance is relaxed to some extent by melting of ice near the interface.

In crystals of double-complex salts [M(bpy)(3)](2)[Cr(CN)(6)]Cl.8H(2)O (M(2+) = Ru(2+), Os(2+); bpy = 2,2'-bipyridine), luminescence from (3)CT state of [M(bpy)(3)](2+) is partially quenched by [Cr(CN)(6)](3)(-) at 77 K and room temperature (RT). This quenching is attributed to intermolecular excitation energy transfer from the (3)CT state of [M(bpy)(3)](2+) to the (2)E(g) state of [Cr(CN)(6)](3)(-). Crystal structure and crystal parameters of [Os(bpy)(3)](2)[Cr(CN)(6)]Cl.8H(2)O: monoclinic, C2, a = 22.384(4) Å, b = 13.827(4) Å, c = 22.186(3) Å, beta = 90.70(2) degrees, V = 6866(2) Å(3), Z = 4, R = 0.0789, R(w) = 0.1932: are almost the same as those of [Ru(bpy)(3)](2)[Cr(CN)(6)]Cl.8H(2)O: monoclinic, C2, a = 22.414(2) Å, b = 13.7686(15) Å, c = 22.207(2) Å, beta = 90.713(8) degrees, V = 6852.9(12) Å(3), Z = 4, R = 0.0554, R(w) = 0.1679. Moreover, these double complex salts have the same distance and relative orientation between donor and acceptor. The rate of intermolecular energy transfer from [M(bpy)(3)](2+) to [Cr(CN)(6)](3)(-) was evaluated by the decay time of luminescence from (3)CT state of [M(bpy)(3)](2+) in single- and double-complex salts. The rate of energy transfer in [Os(bpy)(3)](2)[Cr(CN)(6)]Cl.8H(2)O (4.9 x 10(7) s(-)(1)) is about eight times larger than that in [Ru(bpy)(3)](2)[Cr(CN)(6)]Cl.8H(2)O (6.0 x 10(6) s(-)(1)) at 77 K. The difference of energy transfer rate is brought about by only the spectral overlap between the normalized luminescence spectrum from the (3)CT state of donor ([M(bpy)(3)](2+)) and the normalized excitation spectrum of the (2)E(g) state of acceptor ([Cr(CN)(6)](3)(-)) in the salts. Decay rates of the (3)CT state in [M(bpy)(3)](2)[Cr(CN)(6)]Cl.8H(2)O were measured as a function of temperature. A large enhancement of a decay rate from the (3)CT state was obtained for [Ru(bpy)(3)](2)[Cr(CN)(6)]Cl.8H(2)O as the temperature was increased. This result implies that an additional path from the (3)CT state of [Ru(bpy)(3)](2+) to the (2)T(2g) state of [Cr(CN)(6)](3)(-) would be opened for energy transfer with a rise in temperature in [Ru(bpy)(3)](2)[Cr(CN)(6)]Cl.8H(2)O.

A metal-ligand bond shortening of [AuCl(PPh(3))(2)] by photoexcitation was analyzed by the photocrystallographic method in the unsolvated crystal. The gradual structural change of photoexcited and ground-state molecules with cooling explains the temperature dependence of the emission spectrum and the excited-state lifetime. Actually, on cooling, the ground-state molecular structure approached the excited-state structure. As a result, the HOMO-LUMO gap of [AuCl(PPh(3))(2)] became narrower and a red shift of the absorption and emission bands were observed. Below 180 K, inhibition of the bond shortening was observed due to the intermolecular interactions, which was confirmed by the temperature dependence of the photoexcited phase cell volume, the integrated emission intensity, and the excited-state lifetime measurement.

An aqueous solution separates into ice and a freeze-concentrated solution (FCS) when frozen at temperatures above the eutectic point. The FCS acts as important reaction media in natural environment and industrial processes. The viscosities of the FCS in frozen glycerol/water solutions are evaluated by two spectrometric methods with different principles: (1) the reaction rate of the diffusion-controlled emission quenching and (2) fluorescence correlation spectroscopy. Thermodynamics indicates that the concentration of glycerol in the FCS is constant at a constant temperature regardless of the glycerol concentration in the original solution before freezing (c gly ini). However, the viscosity of the FCS measured at a given temperature increases with decreasing c gly ini, and this trend becomes more pronounced with decreasing measurement temperature. Further, the viscosity of the FCS in a rapidly frozen solution is higher than that in a slowly frozen solution. These results suggest that the viscosity of the FCS depends on the size of the space in which the FCS is confined and is enhanced in smaller spaces. This result agrees well with several reports of anomalous phenomena in a microspace confined in ice. These phenomena should originate from the fluctuation of the ice/FCS interface, which is macroscopically stable but microscopically dynamic and undergoes continuous freezing and thawing. Thus, the FCS near the interface has ice-like physicochemical properties and structures, giving higher viscosity than the corresponding bulk solution.

The photoexcited charge-transferred state of [AuCl(PPh(3))(2)] in a novel polymorphic crystal form was directly observed by X-ray photocrystallographic analysis. Its photoexcited state was completely different from the one generated in the known crystal of [AuCl(PPh(3))(2)]; the photoexcited bond-shrunk state was generated in the known crystal. This difference in the generated photoexcited state was clearly reflected by the difference in emission color. While the known crystal form showed green phosphorescence, the novel form showed blue phosphorescence under UV irradiation. The difference in the generated photoexcited state was due to the differences in steric hindrance in the crystal; bond shortening by photoexcitation was sterically allowed in the known form, while on the other hand, it was restricted in the novel form. Therefore, instead of the bond-shrunk state, the charge-transferred excited state became the lowest triplet state, and the emission color changed from green to blue (i.e., a blue shift of the emission wavelength was observed). These results mean that the photoexcited structure and the emission color of [AuCl(PPh(3))(2)] can be controlled by designing the molecular environment in the crystal.