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

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

doi:10.1071/CH09142

RESEARCH FRONT

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

Toby D. M. Bell ^A , Sheshanath V. Bhosale ^B , Kenneth P. Ghiggino ^A , Steven J. Langford ^B ^C and Clint P. Woodward ^B

+ Author Affiliations

- Author Affiliations

^A School of Chemistry and Bio21 Institute, The University of Melbourne, Parkville, Vic. 3010, Australia.

^B School of Chemistry, Monash University, Clayton, Vic. 3800, Australia.

^C Corresponding author. Email: s.langford@sci.monash.edu.au

Australian Journal of Chemistry 62(7) 692-699 https://doi.org/10.1071/CH09142
Submitted: 11 March 2009 Accepted: 13 May 2009 Published: 13 July 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.

Acknowledgements

The present research was supported by the Australia Research Council’s Discovery Grant Scheme (DP0878220). CPW thanks the Monash University Faculty of Science for support through a Dean’s post-graduate scholarship. TDMB thanks the University of Melbourne for the award of the Faculty of Science Centenary Fellowship. Assistance from Sheryll Yap in carrying out the photophysical measurements is also acknowledged.

References

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

Abstract

Acknowledgements

Subscriber Login