Abstract
The covalently linked chlorophyll a dimer exhibits remarkably different properties in the folded and open configurations. In the folded configuration the absorption maximum is at 695 nm and the fluorescence maximum is at 730 nm. Laser output at 733 and 735 nm is obtained for solutions in wet benzene and 0.1 M ethanol/toluene, respectively. Measurements of fluorescence lineshapes, made with a transverse excited atmospheric (TEA) nitrogen laser for excitation, show the lifetime shortening associated with stimulated emission resulting from appreciable concentrations of molecules in S1 excited states. In contrast, the open dimer has absorption and fluorescence spectra essentially the same as those of chlorophyll a monomer. Unlike either the folded dimer or chlorophyll a monomer, the open dimer shows no laser emission or fluorescene lifetime shortening. It does not appear that the behavior of the open dimer can be explained in terms of excimer or triplet formation or by nonradiative decay processes. It is suggested that absorption of the exciting radiation by S1, leading to the formation of an exciplex or charge transfer state, may be involved. Significantly, no large changes in fluorescence quantum yield or fluorescence lifetime are observed for these dimers as compared to monomer chlorophyll. This suggests that concentration quenching and lifetime shortening in condensed chlorophyll systems involve more than the simple proximity of two chlorophyll molecules.
Keywords: fluorescence, lifetime shortening, excited states
Full text
PDF
Images in this article
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Hindman J. C., Kugel R., Svirmickas A., Katz J. J. Chlorophyll lasers: Stimulated light emission by chlorophylls and Mg-free chlorophyll derivatives. Proc Natl Acad Sci U S A. 1977 Jan;74(1):5–9. doi: 10.1073/pnas.74.1.5. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Latimer P., Bannister T. T., Rabinowitch E. Quantum Yields of Fluorescence of Plant Pigments. Science. 1956 Sep 28;124(3222):585–586. doi: 10.1126/science.124.3222.585. [DOI] [PubMed] [Google Scholar]
- Shapiro S. L., Kollman V. H., Campillo A. J. Energy transfer in photosynthesis: pigment concentration effects and fluorescent lifetimes. FEBS Lett. 1975 Jul 1;54(3):358–362. doi: 10.1016/0014-5793(75)80939-2. [DOI] [PubMed] [Google Scholar]
- Shipman L. L., Cotton T. M., Norris J. R., Katz J. J. An analysis of the visible absorption spectrum of chlorophyll a monomer, dimer,and oligomers in solution. J Am Chem Soc. 1976 Dec 8;98(25):8222–8230. doi: 10.1021/ja00441a056. [DOI] [PubMed] [Google Scholar]
- Wasielewski M. R., Studier M. H., Katz J. J. Covalently linked chlorophyll a dimer: A biomimetic model of special pair chlorophyll. Proc Natl Acad Sci U S A. 1976 Dec;73(12):4282–4286. doi: 10.1073/pnas.73.12.4282. [DOI] [PMC free article] [PubMed] [Google Scholar]