| Abstract
| - Previously reported excitation spectra for eumelanin are sparse and inconsistent. Moreover, these studieshave failed to account for probe beam attenuation and emission reabsorption within the samples, makingthem 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 beamattenuation and emission reabsorption significantly affect the spectra even in low-concentration eumelaninsolutions and that previously published data do not reflect the true excitation profile. We apply a correctionprocedure (previously applied to emission spectra) to account for these effects. Application of this procedurereconstructs the expected relationship of signal intensity with concentration, and the normalized spectra showa similarity in form to the absorption profiles. These spectra reveal valuable information regarding thephotophysics and photochemistry of eumelanin. Most notably, an excitation peak at 365 nm (3.40 eV), whoseposition is independent of emission wavelength, is possibly attributable to a 5,6-dihydroxyindole-2-carboxylicacid (DHICA) component singly linked to a polymeric structure.
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