Takuhiro Otsuka

Polymorphic Crystal Approach to Changing the Emission of [AuCl(PPh3)2], Analyzed by Direct Observation of the Photoexcited Structures by X-ray Photocrystallography

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.

Specific cation effect on quenching reactions of excited tris(α,α′-diimine) ruthenium(II) and chromium(III) complexes by cyanide complexes in aqueous solutions

Abstract Specific salt effects were studied on the quenching reaction of excited [Ru(NN) 3 ] 2+ (NN=2,2′-bipyridine(bpy), 1,10-phenanthrorine(phen)) and [Cr(bpy) 3 ] 3+ by [Cr(CN) 6 ] 3− , [Fe(CN) 6 ] 3− and [Ni(CN) 4 ] 2− in aqueous solutions as a function of alkali metal ions which were added for adjustment of ionic strength. The quenching rate constants in [Ru(NN) 3 ] 2+ –[Cr(CN) 6 ] 3− and [Cr(bpy) 3 ] 3+ –[Cr(CN) 6 ] 3− systems are changed by the cations as Li + >Na + >K + ≈Rb + ≈Cs + . On the other hand, the rate constants in [Ru(NN) 3 ] 2+ –[Fe(CN) 6 ] 3− and [Ru(NN) 3 ] 2+ –[Ni(CN) 4 ] 2− systems, which are diffusion-controlled reactions, are not varied by the alkali metal cations. The obtained order (Li + >Na + >K + ≈Rb + ≈Cs + ) of the quenching rate constant is quite different from salt effects, Li + + + + + , which have been obtained in the electron transfer reactions between complex anions.

Energy Transfer From Tris(2,2′-Bipyridine)Ruthenium(II) or Tris(2,2′-Bipyridine)Osmium(II) To Hexacyanochromate(III) in a Pure Crystal of Double Complex Salt

Abstract It is clarified by performing X-ray structure analysis that the crystal structure of [Ru(bpy)3]2[Cr(CN)6]CI·8H2O (bpy = 2,2′-bipyridine) is the same as that of [Os(bpy)3]2[Cr(CN)6]Cl·8H2O. The difference of energy transfer rate from [M(bpy)3]2+ (M=Ru2+ or Os2+) to [Cr(CN)6]3- in pure crystals of double complex salts ([M(bpy)3]2[Cr(CN)6]Cl·8H2O) is discussed in terms of the spectroscopic characters and lifetimes of the salts.

On the spin-polarization in the ground state of the Cr(III) ion

Abstract The emissive and followed absorptive time-resolved ESR signals of the ground state (4A2g) of the Cr(III) ion were observed in ruby after irradiation of the second harmonics of a Nd:YAG laser. Abnormal spin-polarization occurred at the ground state sublevels by laser excitation over sub-milliseconds. The spin-polarization in the sublevels of 4A2g is discussed.