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Research has been conducted on the energy transfer between transition-metal complexes in crystals. The relationship between the energy-transfer rate and donor-acceptor orientation in double-complex salts has been investigated via the spectral overlap manipulations.

The relationship of energy-transfer rates and spectroscopic character in the double-complex salts (M(bpy)3)2(Cr(CN)6)Cl.8H2O, where M2+ = Ru2+, Os2+; bpy = 2.12'-bipyridine, has been investigated. The results showed that the luminescence from 3CT state of (M(bpy)3)2+ is partially quenched by (Cr(CN)6)3- at 77 degrees Kelvin and room temperature. The quenching is attributed to intermolecular excitation energy transfer from 3CT state of (M(bpy)3)2+ to the 2Eg state of (Cr(CN)6)3-.

The time-resolved ESR (TR-ESR) signals for ground-state of Cr(III) ion were studied in ruby and of Cr(acac) doped in Al(acac) single crystals after irradiation with the second harmonic of a Nd:YAG laser at 77 K. TR-ESR was seen in ruby but not in Cr(acac) at room temperature. Both spectra at 77 K were of the emissive kind. However, the intensity of the Cr(acac) signal was very weak. The TR-ESR in ruby was altered from emissive polarity to an absorptive one at 700 microsec.

A metal-ligand bond shortening of [AuCl(PPh3)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(PPh3)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. [ABSTRACT FROM AUTHOR]

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(ox)3]3− (ox=oxalate ion) and [Cr(mal)3]3− (mal=malonate ion) in aqueous solutions as a function of alkali metal ions which were added for adjustment of ionic strength. The value of kq, quenching rate constants, and k1, energy transfer rate constant in encounter complex, is changed by the cations as the order of Li+ > Na+ > K+ ≈ Rb+ ⩽ Cs+, although diffusion rate constants are not changed by the co-existing cations. Among the quenching reactions investigated in this work, a ratio of k1 values in the aqueous solutions whose ionic strength was adjusted with LiCl and KCl, k1LiCl/k1KCl, is larger for quenching systems of closely approached donor-acceptor pair than loosely bounded pair. These results indicate that co-existing alkali cation tunes the distance between donor and acceptor in encounter complex where energy transfer occurs. [Copyright &y& Elsevier]

Abstract: Specific cation and anion effects are investigated on reactions of energy transfer from [Tb(dpa)3]3− (dpa=2,6-pyridinedicarboxylate) to [Co(bpy)3]3+ (bpy=2,2′-bipyridine), [Co(en)3]3+ (en=ethylenediamine), [Co(pam)3]3+ (pam=2-aminomethylpyridine) and [Co(NH3)6]3+ in aqueous solutions. Quenching rate constants of [Tb(dpa)3]3− by [Co(bpy)3]3+ are changed by the added anions in the following order, Cl− >Br− >ClO4 −. However, the order of the quenching rate constants of [Tb(dpa)3]3− by [Co(en)3]3+, [Co(pam)3]3+ and [Co(NH3)6]3+ is different, Cl− ≈Br−