LOW-LYING ELECTRONIC STATES OF [RH(BPY)(3)](3- A COMPARATIVE-STUDY BASED ON HIGHLY RESOLVED AND TIME-RESOLVED SPECTRA(), [PT(BPY)(2)](2+), AND [RU(BPY)(3)](2+) )

Optical emission and excitation spectra of [Rh(bpy-h(8))(3)](3+), [Rh( bpy-h(8))(2)(bpy-d(8))](3+), [Rh(bpy-d(8))(3)](3+), [Pt(bpy-h(8))(2)]( 2+), [Pt(bpy-d(8))(bpy-d(8))](2+), [Pt(bpy-d(8))(2)](2+), [Ru(bpy-h(8) )(3)](2+), [Ru(bpy-h(8))(2)(bpy-d(8))](2+), and [Ru(bpy-d(8))(3)](2+) are discussed. A series of trends-also including [Os(bpy)(3)](2+)-is u ncovered. These trends, which are connected with an increase in metal- d or MLCT character in the lowest triplet states, call for instance be seen in transition energies, emission lifetimes, zero-field splitting s, rates of spin-lattice relaxation, vibronic satellite structures, an d changes of nuclear equilibrium positions on excitation. Moreover, th e compounds investigated are also appropriate for consideration of the concept of ''dual emission'', the relation between MLCT character and covalency, as well as the current models of localization/delocalizati on. Ln particular, a comparison of the properties of [Rh(bpy)(3)](3+)- and [Ru(bpy)(3)](2+)-doped [Zn(bpy)(3)](ClO4)(2) provides illustrativ e and very strong evidence for covalent delocalization in the lowest e xcited states of [Ru/bpy)(3)](2+), while ligand-centered localization is found in the states of [Rh(bpy)(3)](3+). Misinterpretations might o ccur if the aggregation effects of the chromophores are not taken into account. (C) 1997 Elsevier Science S.A.