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Radiative Relaxation Quantum Yields for Synthetic Eumelanin ¶
Author(s) -
Meredith Paul,
Riesz Jennifer
Publication year - 2004
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.2004.tb00012.x
Subject(s) - quantum yield , photoluminescence , radiative transfer , chemistry , relaxation (psychology) , excitation , yield (engineering) , radiant energy , quantum , atomic physics , range (aeronautics) , emission spectrum , spontaneous emission , quantum efficiency , vibrational energy relaxation , molecular physics , spectral line , radiation , materials science , optics , optoelectronics , molecule , physics , fluorescence , laser , psychology , social psychology , quantum mechanics , astronomy , metallurgy , organic chemistry , composite material
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.