A new approach to the measurement of luminescence rise times is described which eliminates the problems associated with different transit times of the photomultiplier for different wavelengths. The approach is based on a wavelength shifter with a very long lifetime. The method and a suitable wavelength shifter are described. The technique is used to study the rise times of photochemically important cis-[RhL,(XY)]+ complexes where L = 2,2'-bipyridine, 1,lO-phenanthroline, or ethylenediamine and X, Y = C1-, Br-. In the best cases, with a 10-ns excitation pulse, the method shows rise times to be 50.1 ns. Relaxation pathways and photochemical implications are discussed.There is currently great interest in the photochemical and luminescence properties of transition metal complexes.ld Fundamental to understanding and practical utilization of these processes in such areas as solar energy conversion and laser technology is knowledge of the paths and rates of intramolecular energy degradation. This information has proved exceedingly elusive.Luminescence rise time measurements are potentially a very powerful tool for directly studying intramolecular relaxation phenomena of the following type:where D is a luminescent species, **D is the species in an initially excited upper excited state, and *D is the thermally equilibrated excited state from which emission arises. T , is the rise time associated with relaxation to the emitting level, and 7 D is the decay time of the emitting level. In principle, T , is not a simple decay time, but the available data rarely justify a more complex treatment. In practice, T , would be measured by exciting the sample with a short optical pulse and monitoring the grow-in of the luminescence of *D. The use of luminescence rise times to measure 7, has not been completely satisfactory. Initially, workers using the luminescence risetime method reported microsecond rise times for Cr(II1) complexe~,~ but other workers using the same technique showed these measurements to be in error; the true values were 110-100 Picosecond absorption techniques have now shown Cr(II1) complexes to have 7;s in the low picosecond range.gWe were particularly intrigued by the report of Ohashi et al.lOa on Rh(II1) complexes. These authors reported that solid samples of cis-[Rh(bpy),X,]X exhibited 7,'s of 350-630 ns where bpy = 2,2'-bipyridine and X = C1-or Br-.These results were interpreted as a hindered relaxation from a ligand-localized 3(7r-71.*) state to the emitting metal localized 3(d-d) state.loa Rhodium(II1) complexes have played a central role in the understanding of the photochemical and photophysical processes of d6 complexes.ll2 The reported slow rise times, if correct, have important and wide-ranging ramifications in the interpretation, and practical utilization, of transition metal complexes. We have carefully reexamined the claimed long 7,'s of the [Rh(bpy)zXz]X species as well as the analogous phen (1,lO-phenanthroline) and similar cisbis(ethy1enediamine) samples. Our results conclusively show that the ris...
Der adsorbierte Komplex zeigt die gleichen spektralen Eigenschaften wie der in flüssiger Lösung.
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