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- W2949691860 abstract "A series of Cr/sup III/(PP)/sub x/X/sub 6-2n/ complexes have been prepared and characterized in which n = 1 or 2, PP = 2,2'-bipyridine or 1,10-phenanthroline, and X = NH/sub 3/, en/2, acac/sup /minus///2, CN/sup /minus//, or NCS/sup /minus//. The (/sup 2/E)Cr/sup III/(PP)/sub n/X/sub 6-2n/ excited states are much weaker oxidants than their (/sup 2/E)Cr(PP)/sub 3//sup 2+/ parents. The visible spectroscopy of the Cr/sup III/(PP)/sub n/X/sub 6-2n/ complexes is complicated by overlapping absorptions. A very prominent feature of these absorptions is a regular, relatively narrow band progression with energies independent of X. This progression is attributed to direct excitation into the triplet-/pi/* ligand manifold states, with the forbidden singlet-triplet transitions of the free polypyridyl ligand(s) being relaxed by spin-spin coupling in the Cr(III) complexes. The (/sup 2/E)Cr(III) lifetimes, /tau/(/sup 2/E), of these complexes in fluid and glass solutions are strongly temperature dependent but approach a limiting value at low temperatures: (/tau/(/sup 2/E))/sup /minus/1/ = k/sub r/ + k/sub nr//sup 0/ + A exp(/minus/E/sub a//RT), where k/sub r/ and k/sub nr//sup 0/ are the nearly temperature-independent radiative and nonradiative relaxation rate constants, respectively. The room-temperature lifetimes of the mixed-ligand complexes vary over a 30-fold range, and /tau/(/sup 2/E) is much smaller formore » these complexes than found for their Cr(phen)/sub 3//sup 3+/ and Cr(bpy)/sub 3//sup 3+/ parents. The range of lifetimes is not strongly temperature dependent since E/sub a/ = 33 /plus minus/ 2 kJ mol/sup /minus/1/ and A = (3.5 /plus minus/ 1.1) /times/ 10/sup 11/ s/sup /minus/1/ for the Cr/sup III/(PP)/sub n/X/sub 6-2n/ complexes (X ne CN/sup /minus//); for X = CN/sup /minus//, A /approx/ 7 /times/ 10/sup 12/ s/sup /minus/1/. 65 references, 8 figures, 9 tables.« less" @default.
- W2949691860 created "2019-06-27" @default.
- W2949691860 creator A5044487475 @default.
- W2949691860 creator A5062915614 @default.
- W2949691860 date "1988-10-25" @default.
- W2949691860 modified "2023-09-27" @default.
- W2949691860 title "ChemInform Abstract: Synthesis, Spectroscopy, and Photophysical Behavior of Mixed-Ligand Mono- and Bis(polypyridyl)chromium(III) Complexes. Examples of Efficient, Thermally Activated Excited-State Relaxation Without Back Intersystem Crossing." @default.
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- W2949691860 doi "https://doi.org/10.1002/chin.198843288" @default.
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