Luminescent ligand-to-metal charge-transfer excited states based on pentamethylcyclopentadienyl complexes of tantalum
- Univ. of Wyoming, Laramie, WY (United States)
- E.I du Pont Corporation, Wilmington, DE (United States)
Understanding of the photochemistry and photophysics of complexes with metal-to-ligand charge-transfer (MLCT) excited states has developed rapidly, evolving to the point that application to energy conversion processes is now a predominant focus. This success can be traced directly to an understanding of the photophysics and photochemistry of complexes of the type M (bpy){sub 3}{sup n+ } (M is Ru, n is 2; M is Os, n is 2; M is Ir, n is 3) and M(bpy){sub 2}L{sub 2}{sup 2+} (M is Ru and Os, and L can be a variety of neutral 2-electron donor ligands), which has reached a level of sophistication so that design of chemically stable photosensitizers with prescribed excited-state lifetimes and redox potentials can be realized by synthetic manipulation of the coordination sphere. Despite this success, there exists a whole class of complexes whose excited-state properties has been largely ignored-those containing ligand-to-metal charge transfer (LMCT) excited states. Early examples of photochemical reactions from LMCT excited states are found in the classical series Co {sub III} (NH{sub 3}){sub 5}X{sup 2}, where charge transfer from halide to Co(III) results in photoreduction to Co(II) and the formation of halide radicals. To discover new LMCT excited states, complexes which contain oxidizable donor ligands coordinated to early or middle transition metal of d{sup 0} like Ta(V) were investigated. Reported are the excited-state properties of the complex Cp*TaCl{sub 4} and the derivative Cp*TaCl{sub 3}(OO) (where OO is a bidentate oxygen donor such a a corboxylic or sulfonic acid) which exhibit long-lived luminescence in fluid solution and can have quantum efficiencies for emission of up to 16% (at 23 degrees C). For each complex, the photophysical parameters are included.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 457462
- Journal Information:
- Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 17 Vol. 114; ISSN JACSAT; ISSN 0002-7863
- Country of Publication:
- United States
- Language:
- English
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