Electronic Energy Self-Exchange with Macrocyclic Chromium(III) Complexes
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- 作者：Paul S. Wagenknecht ; Noel A. P. Kane-Maguire ; David G. Speece ; and Nancy Helwic
- 刊名：Inorganic Chemistry
- 出版年：2002
- 出版时间：March 11, 2002
- 年：2002
- 卷：41
- 期：5
- 页码：1229 - 1235
- 全文大小：75K
- 年卷期：v.41,no.5(March 11, 2002)
- ISSN：1520-510X
文摘
The luminescence lifetimes of N-deuterated Cr(III) complexes of macrocyclic tetraamine ligands, trans-CrN4X2n+,are substantially longer than those of their undeuterated counterparts in room temperature solution. Thus, excited-state emission quenching of the longer lived species by the shorter lived species may be studied by analyzing thedecay profile following pulsed excitation. Flash photolysis experiments were carried out for three deuterated/undeuterated pairs of trans-CrN4X2n+ complexes (where X = CN-, NH3, and F-). For the trans-Cr(cyclam)(CN)2+system in H2O, it was determined that energy transfer was occurring between the deuterated and undeuteratedspecies. Although the rate constant of energy transfer was too fast to measure explicitly, it could be bracketed asket 
7 × 106 M-1 s-1. For this reaction it was possible to measure an equilibrium constant which was very near1.0. For trans-Cr(cyclam)(NH3)23+ in DMSO, it was also established that energy transfer was occurring and rateconstants of 2.4 × 106 M-1 s-1 (
= 0.1) and 9.7 × 106 M-1 s-1 ( = 1.0) were determined by a Stern-Volmeranalysis. For trans-Cr(tet a)F2+ in H2O, no energy transfer was observed, which implies that the rate constant is
3 × 105 M-1 s-1. Because these energy-transfer reactions represent self-exchange energy transfer and are thusthermoneutral, we are able to analyze the results using Marcus theory and draw some conclusions about therelative importance of nuclear reorganization and electronic factors in the overall rate.
7 × 106 M-1 s-1. For this reaction it was possible to measure an equilibrium constant which was very near1.0. For trans-Cr(cyclam)(NH3)23+ in DMSO, it was also established that energy transfer was occurring and rateconstants of 2.4 × 106 M-1 s-1 ( = 0.1) and 9.7 × 106 M-1 s-1 ( = 1.0) were determined by a Stern-Volmeranalysis. For trans-Cr(tet a)F2+ in H2O, no energy transfer was observed, which implies that the rate constant is3 × 105 M-1 s-1. Because these energy-transfer reactions represent self-exchange energy transfer and are thusthermoneutral, we are able to analyze the results using Marcus theory and draw some conclusions about therelative importance of nuclear reorganization and electronic factors in the overall rate.