The nonradiative decay of the lowest electronically excited triplet states (3MLCT) of the title compound is studied and discussed on the basis of a previously developed theoretical framework. Extensive data on the luminescence lifetimes and resonance Raman intensities for a number of deuteriated analogues have been obtained in order to establish the role of the skeletal bipyridine vibrations in the nonradiative deactivation process. Careful inspection of the results documents position-dependent deuteriation effects on the nonradiative decay rate for R~(bpy)3~+. A model of the nonradiative decay process, incorporating the frequencies and intensities of a large number of totally symmetric acceptor vibrations, has been applied to the data for all the available isotopomers. A weak correlation between the observed and calculated relative nonradiative decay rates exists when only acceptor modes are assumed to vary with ligand deuteriation. However, inclusion of non-totally symmetric in-plane promoter vibrations yields calculated rates which are in an excellent agreement with the experimental data. IntroductionThe nonradiative relaxation of electronically excited states, whereby excess electronic energy is dissipated to the surroundings via vibrationally mediated processes, is an issue of fundamental importance for gaining a detailed understanding of the photophysics and photochemistry of polyatomic molecules. While there has been an extensive development of the theoretical framework for dealing with radiationless it is obviously difficult to devise effective experimental approaches to this issue inasmuch as the actual processes are not conveniently observable, the excited state lifetime being the only direct parameter that is experimentally accessible.Given this situation, the approach generally taken is to acquire lifetime data as a function of variable environmental factors (e.g., solvent and temperature).I0-l5 In addition to these "external" variations, the study of deuteriation effects on the measured lifetimes can potentially provide valuable insight into the precise mechanisms of nonradiative p r o c e s~e s .~~'~-~~ Generally, deuteriation results in a decrease in nonradiative decay. For example, substantial increases in the triplet state lifetimes upon perdeuteriation were observed for naphthalene.3.'6.'8-20 This approach was extended in studies which demonstrated a lifetime dependence not only on the number of deuterium substituents but also on the position of s u b s t i t u t i~n .~. '~-~~ Similar studies2',22 have been carried out for the long lived (600 ns) 3MLCT excited state of the tris(bipyridine)ruthenium-(11) complex, R~(bpy)3~+, which is of intense interest as the paradigm of a series of compounds having great potential for solar energy conversion scheme^.^^-*^ Thus, perdeuteriation of the ligand increases the lifetime of the 3MLCT state from -600 to -700 ns (at room temperature in aqueous solutions).2' In addition, in a preliminary report, we have documented in this case also a position-dependent de...

Several homoleptic and bis-heteroleptic tris-ligated polypyridine complexes of Ru(II) have been prepared in the zeolite Y supercages. Ru(L)"(L')3-"-Y (where = 0, 1, 2, 3 and L, U = bpy, dmb, mmb, and bpz) complexes have been investigated by electronic absorption, electronic emission, resonance Raman, and time-resolved resonance Raman spectroscopies. Excited-state lifetimes of the entrapped complexes have been measured and their temperature dependence established. While entrapment of the complexes in the zeolite matrix introduces no major modifications in structure or electron distribution, it does induce changes in the efficiency of various excited state energy dissipation pathways, the major effect being an increase in the energy of the metal-centered dd excited states which leads to elimination of one of the major decay and decomposition pathways.

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A novel synthetic strategy for the preparation of organized molecular assemblies entrapped within the supercage network of Y-zeolite is described. A molecular assembly composed of two Ru(II)−polypyridine complexes, Ru(bpy)2bpz2+ and Ru(mmb)3 2+ (where bpy = 2,2‘-bipyridine, bpz = 2,2‘-bipyrazine, and mmb = 5-methyl-2,2‘-bipyridine), entrapped in adjacent supercages, has been prepared and characterized by diffuse reflectance, resonance Raman and electronic emission spectroscopy, and excited-state lifetime measurements. A dramatic (∼2.5−4-fold) decrease in the emission intensity of the adjacent cage assembly, compared to a sample in which the two complexes are distributed randomly (RM) or in separate particles (MM), indicates strong interaction between the adjacent complexes. The results of the excited-state lifetime measurements are consistent with this observation. Thus, in the emission decay profile of the assembly, a new short-lived component (∼30 ns), attributable to the emission from the interacting dyad molecules, has been observed. While this short component dominates the emission decay for the adjacent cage assembly, it is not observed in the mechanical mixture (MM) and is too small to be accurately determined in the randomized sample (RM).