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Biophys J. 2008 Nov 1;95(9):4396-402. doi: 10.1529/biophysj.108.135756. Epub 2008 Aug 1.

Mechanisms for ultrafast nonradiative relaxation in electronically excited eumelanin constituents.

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  • 1Department of Physics and School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA.


We 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 approximately 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.

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