  The quantum yield of synthetic eumelanin is known to be extremely low and it
has recently been reported to be dependent on excitation wavelength. In this
paper, we present quantum yield as a function of excitation wavelength between
250 and 500 nm, showing it to be a factor of 4 higher at 250 nm than at 500 nm.
In addition, we present a definitive map of the steady-state fluorescence as a
function of excitation and emission wavelengths, and significantly, a
three-dimensional map of the specific quantum yield: the fraction of photons
absorbed at each wavelength that are subsequently radiated at each emission
wavelength. This map contains clear features, which we attribute to certain
structural models, and shows that radiative emission and specific quantum yield
are negligible at emission wavelengths outside the range of 585 and 385 nm (2.2
and 3.2 eV), regardless of excitation wavelength. This information is important
in the context of understanding melanin biofunctionality, and the quantum
molecular biophysics therein.
