<p>Although the role of excited triplet states in aerobic photochemistry of melanin pigments has been implicated, the molecular origin of the melanin subunits excited to triplet states and their key thermodynamic parameters remain unknown. Reactive oxygen species photogenerated by melanin may be involved in degradation of the pigment leading to impairment of its biological functions. To address photochemical aspects of this problem, selected diene probes were used. These probes exhibited high efficiency in quenching the excited triplet state of synthetic eumelanin and pheomelanin responsible for generation of singlet oxygen. The results indicate that photoexcitation of the melanins generated at least two different pools of triplet excited states with different energies and accessibility to the diene probes. The data confirm that singlet oxygen is photogenerated by energy transfer from the melanin triplet excited states to dioxygen. The high efficiency of the dienes in quenching the excited triplet states of melanin may provide protection against photoaging of human retinal pigment epithelium melanin.</p>