Source:http://linkedlifedata.com/resource/pubmed/id/19006413
Switch to
| Predicate | Object |
|---|---|
| rdf:type | |
| lifeskim:mentions | |
| pubmed:issue |
46
|
| pubmed:dateCreated |
2008-11-13
|
| pubmed:abstractText |
Excited-state charge separation in molecular architectures has been widely explored, yet ground-state hole (or electron) transfer, particularly involving equivalent pigments, has been far less studied, and direct quantitation of the rate of transfer often has proved difficult. Prior studies of ground-state hole transfer between equivalent zinc porphyrins using electron paramagnetic resonance techniques give a lower limit of approximately (50 ns)(-1) on the rates. Related transient optical studies of hole transfer between inequivalent sites [zinc porphyrin (Zn) and free base porphyrin (Fb)] give an upper limit of approximately (20 ps)(-1). Thus, a substantial window remains for the unknown rates of ground-state hole transfer between equivalent sites. Herein, the ground-state hole-transfer processes are probed in a series of oxidized porphyrin triads (ZnZnFb) with the focus being on determination of the rates between the nominally equivalent sites (Zn/Zn). The strategy builds upon recent time-resolved optical studies of the photodynamics of dyads wherein a zinc porphyrin is electrochemically oxidized and the attached free base porphyrin is photoexcited. The resulting energy- and hole-transfer processes in the oxidized ZnFb dyads are typically complete within 100 ps of excitation. Such processes are also present in the triads and serve as a starting point for determining the rates of ground-state hole transfer between equivalent sites in the triads. The rate constant of the Zn/Zn hole transfer is found to be (0.8 ns)(-1) for diphenylethyne-linked zinc porphyrins and increases only slightly to (0.6 ns)(-1) when a shorter phenylene linker is utilized. The rate decreases slightly to (1.1 ns)(-1) when steric constraints are introduced in the diarylethyne linker. In general, the rate constants for ground-state Zn/Zn hole transfer in oxidized arrays are a factor of 40 slower than those for Zn/Fb transfer. Collectively, the findings should aid the design of next-generation molecular architectures for applications in solar-energy conversion.
|
| pubmed:language |
eng
|
| pubmed:journal | |
| pubmed:status |
PubMed-not-MEDLINE
|
| pubmed:month |
Nov
|
| pubmed:issn |
1520-5126
|
| pubmed:author | |
| pubmed:issnType |
Electronic
|
| pubmed:day |
19
|
| pubmed:volume |
130
|
| pubmed:owner |
NLM
|
| pubmed:authorsComplete |
Y
|
| pubmed:pagination |
15636-48
|
| pubmed:year |
2008
|
| pubmed:articleTitle |
Determination of ground-state hole-transfer rates between equivalent sites in oxidized multiporphyrin arrays using time-resolved optical spectroscopy.
|
| pubmed:affiliation |
Department of Chemistry, Washington University, St. Louis, Missouri 63130-4889, USA.
|
| pubmed:publicationType |
Journal Article
|