Meng, ShengKaxiras, Efthimios2019-09-202008Meng, Sheng, and Efthimios Kaxiras. 2008. “Mechanisms for Ultrafast Nonradiative Relaxation in Electronically Excited Eumelanin Constituents.” Biophysical Journal 95 (9): 4396–4402. https://doi.org/10.1529/biophysj.108.135756.0006-34951542-0086http://nrs.harvard.edu/urn-3:HUL.InstRepos:41384051We investigate the relaxation dynamics of melanin model constituents including monomers, dimers, and tetramers, upon excitation, using state-of-the-art, time-dependent, density functional theory calculations. The results explain the ability of these molecules to transform photon energy into thermal energy in a remarkably short timescale of similar to 100 fs. We find that after electronic excitation by light absorption, ultrafast energy conversion takes place through two novel mechanisms: proton transfer on a timescale of 110 fs and state mixing upon oligomerization on a timescale of < 50 fs. These results are in good agreement with available experiments and help elucidate melanin's role in photoprotection against ultraviolet radiation.en-USJournal Article2019-09-2010.1529/biophysj.108.135756