Nighswander-Rempel Stephen P, Riesz Jennifer, Gilmore Joel, Bothma Jacques P, Meredith Paul
Centre for Biophotonics and Laser Science and Soft Condensed Matter Theory Group, School of Physical Sciences, University of Queensland, St. Lucia, QLD 4067, Australia.
J Phys Chem B. 2005 Nov 3;109(43):20629-35. doi: 10.1021/jp053704+.
Previously reported excitation spectra for eumelanin are sparse and inconsistent. Moreover, these studies have failed to account for probe beam attenuation and emission reabsorption within the samples, making them qualitative at best. We report for the first time quantitative excitation spectra for synthetic eumelanin, acquired for a range of solution concentrations and emission wavelengths. Our data indicate that probe beam attenuation and emission reabsorption significantly affect the spectra even in low-concentration eumelanin solutions and that previously published data do not reflect the true excitation profile. We apply a correction procedure (previously applied to emission spectra) to account for these effects. Application of this procedure reconstructs the expected relationship of signal intensity with concentration, and the normalized spectra show a similarity in form to the absorption profiles. These spectra reveal valuable information regarding the photophysics and photochemistry of eumelanin. Most notably, an excitation peak at 365 nm (3.40 eV), whose position is independent of emission wavelength, is possibly attributable to a 5,6-dihydroxyindole-2-carboxylic acid (DHICA) component singly linked to a polymeric structure.
先前报道的真黑素激发光谱稀少且不一致。此外，这些研究未能考虑样品内探测光束的衰减和发射光的再吸收，充其量只能算是定性研究。我们首次报道了合成真黑素的定量激发光谱，该光谱是在一系列溶液浓度和发射波长下获得的。我们的数据表明，即使在低浓度真黑素溶液中，探测光束的衰减和发射光的再吸收也会显著影响光谱，而且先前发表的数据并未反映真实的激发谱。我们应用一种校正程序（先前应用于发射光谱）来考虑这些影响。应用此程序可重建信号强度与浓度的预期关系，归一化后的光谱在形式上与吸收谱相似。这些光谱揭示了有关真黑素光物理和光化学的有价值信息。最值得注意的是，在365 nm（3.40 eV）处的一个激发峰，其位置与发射波长无关，可能归因于与聚合物结构单链相连的5,6 - 二羟基吲哚 - 2 - 羧酸（DHICA）成分。
