Fig. 5. Simple illustrations of ground state bleach dynamics arising from possible excited state decay pathways in DOPA melanin. Examples are shown for 4 discrete chromophores that absorb at different energies as shown in (a). For illustration, the chromophore with the highest energy transition is excited (black vertical arrow). In uncoupled chromophores (b), only the excited chromophore is bleached; the bleach recovers over time due to excited state relaxation. In a system of coupled chromophores (c and d), additional chromophores can be bleached. (c) Energy migration by excitation energy transfer (EET) causes the bleach to redshift over time as energy is funneled from the excited chromophore to lower energy chromophores during excited state relaxation. (d) Charge transfer (CT) from the excited chromophore to neighboring chromophores forms charge transfer excitons that cause bleaching of all chromophores. The bleaching is strongest by the initially excited chromophore. Charge recombination restores the ground states, causing the bleach signals of the excited chromophore and its neighbors to decay in unison.