Radiative Relaxation Quantum Yields for Synthetic Eumelanin

Authors

  • Paul Meredith,

    Corresponding author
    1. Department of Physics and Centre for Biophotonics and Laser Science, University of Queensland, Brisbane, Queensland, Australia
      *Tow whom correspondence should be addressed at: Department of Physics, University of Queensland, St. Lucia, Brisbane, Queensland 4072, Australia. Fax: 617-3365-1242; e-mail: meredith@physics.uq.edu.au
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  • Jennifer Riesz

    1. Department of Physics and Centre for Biophotonics and Laser Science, University of Queensland, Brisbane, Queensland, Australia
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  • Posted on the website on 8 January 2004.

*Tow whom correspondence should be addressed at: Department of Physics, University of Queensland, St. Lucia, Brisbane, Queensland 4072, Australia. Fax: 617-3365-1242; e-mail: meredith@physics.uq.edu.au

ABSTRACT

We report absolute values for the radiative relaxation quantum yield of synthetic eumelanin as a function of excitation energy. These values were determined by correcting for pump beam attenuation and emission reabsorption in both eumelanin samples and fluorescein standards over a large range of concentrations. Our results confirm that eumelanins are capable of dissipating >99.9% of absorbed UV and visible radiation through nonradiative means. Furthermore, we have found that the radiative quantum yield of synthetic eumelanin is excitation energy dependent. This observation is supported by corrected emission spectra, which also show a clear dependence of both peak position and peak width on excitation energy. Our findings indicate that photoluminescence emission in eumelanins is derived from ensembles of small chemically distinct oligomeric units that can be selectively pumped. This hypothesis lends support to the theory that the basic structural unit of eumelanin is oligomeric rather than heteropolymeric.

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