The emission properties of eumelanin from Sepia officinalis are examined fo
llowing UV-A excitation. The emission decay is nonexponential, exhibiting d
ecay components on the tens of picosecond to several nanosecond time scales
. The corresponding depolarization dynamics are also nonexponential and rev
eal that the emission becomes totally depolarized with an average time cons
tant of similar to 80 ps at 20 degrees C. The depolarization of the emissio
n is found to be activated; a simple Arrhenius fit to the depolarization ra
te data gives an activation barrier of 21 +/- 3 kJ mol(-1). The nonexponent
ial emission decay is concluded to be a reflection of the structural disord
er of eumelanin. The rapid and nonexponential depolarization dynamics are a
ttributed to energy transfer processes that occur within "spherical" subuni
ts that comprise the eumelanin aggregates.