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Synthesis and Photophysical Properties of a Conformationally Flexible Mixed Porphyrin Star-Pentamer

Authors :
Sheshanath V. Bhosale
Clint Peter Woodward
Kenneth P. Ghiggino
Toby D. M. Bell
Steven J. Langford
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