Meredith Paul, Riesz Jennifer
Department of Physics, University of Queensland, Brisbane, Queensland, Australia.
Photochem Photobiol. 2004 Feb;79(2):211-6. doi: 10.1562/0031-8655(2004)079<0211:rcrqyf>2.0.co;2.
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.
我们报告了合成真黑素的辐射弛豫量子产率的绝对值与激发能量的函数关系。这些值是通过校正真黑素样品和荧光素标准品在大范围浓度下的泵浦光束衰减和发射再吸收来确定的。我们的结果证实，真黑素能够通过非辐射方式耗散超过99.9%的吸收紫外线和可见光辐射。此外，我们发现合成真黑素的辐射量子产率与激发能量有关。校正后的发射光谱支持了这一观察结果，该光谱还显示出峰值位置和峰值宽度都明显依赖于激发能量。我们的研究结果表明，真黑素中的光致发光发射源自可被选择性泵浦的化学性质不同的小寡聚体单元的集合。这一假设支持了真黑素的基本结构单元是寡聚体而非杂聚物的理论。
