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Synthesis and Photophysical Properties of a Conformationally Flexible Mixed Porphyrin Star-Pentamer
- Source :
- Australian Journal of Chemistry. 62:692
- Publication Year :
- 2009
- Publisher :
- CSIRO Publishing, 2009.
-
Abstract
- The synthesis of a porphyrin star-pentamer bearing a free-base porphyrin core and four zinc(ii) metalloporphyrins, which are tethered by a conformationally flexible linker about the central porphyrin’s antipody, is described. The synthetic strategy is highlighted by the use of olefin cross metathesis to link the five chromophores together in a directed fashion in high yield. Photoexcitation into the Soret absorption band of the zinc porphyrin chromophores at 425 nm leads to a substantial enhancement of central free-base porphyrin fluorescence, indicating energy transfer from the photoexcited zinc porphyrin (outer periphery) to central free-base porphyrin. Time-resolved fluorescence decay profiles required three exponential decay components for satisfactory fitting. These are attributed to emission from the central free-base porphyrin and to two different rates of energy transfer from the zinc porphyrins to the free-base porphyrin. The faster of these decay components equates to an energy-transfer rate constant of 3.7 × 109 s–1 and an efficiency of 83%, whereas the other is essentially unquenched with respect to reported values for zinc porphyrin fluorescence decay times. The relative contribution of these two components to the initial fluorescence decay is ~3:2, similar to the 5:4 ratio of cis and trans geometric isomers present in the pentamer.
Details
- ISSN :
- 00049425
- Volume :
- 62
- Database :
- OpenAIRE
- Journal :
- Australian Journal of Chemistry
- Accession number :
- edsair.doi...........7833caf38483584ce783e4fb61b1fd7a
- Full Text :
- https://doi.org/10.1071/ch09142