Title

Electronic Energy Self-Exchange with Macrocyclic Chromium(III) Complexes

ACS Citation

Wagenknecht, P. S.; Kane-Maguire, N.; Speece, D. G.; Helwic, N. Electronic Energy Self-Exchange with Macrocyclic Chromium(III) Complexes. Inorg. Chem. 2002, 41, 1229-1235.

Abstract

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 the decay 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 undeuterated species. Although the rate constant of energy transfer was too fast to measure explicitly, it could be bracketed as ket ? 7 ? 106 M-1 s-1. For this reaction it was possible to measure an equilibrium constant which was very near 1.0. For trans-Cr(cyclam)(NH3)23+ in DMSO, it was also established that energy transfer was occurring and rate constants 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?Volmer analysis. 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 thus thermoneutral, we are able to analyze the results using Marcus theory and draw some conclusions about the relative importance of nuclear reorganization and electronic factors in the overall rate. 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 the decay 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 undeuterated species. Although the rate constant of energy transfer was too fast to measure explicitly, it could be bracketed as ket ? 7 ? 106 M-1 s-1. For this reaction it was possible to measure an equilibrium constant which was very near 1.0. For trans-Cr(cyclam)(NH3)23+ in DMSO, it was also established that energy transfer was occurring and rate constants 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?Volmer analysis. 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 thus thermoneutral, we are able to analyze the results using Marcus theory and draw some conclusions about the relative importance of nuclear reorganization and electronic factors in the overall rate.

Source Name

Inorganic Chemistry

Publication Date

1-1-2002

Volume

41

Issue

5

Page(s)

125-142

Document Type

Citation

Citation Type

Article