  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 normalised 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 DHICA component singly linked to a
polymeric structure.
