Mechanisms for ultrafast nonradiative relaxation in electronically excited eumelanin constituents.
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.
Meng
Sheng
S
Department of Physics and School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA.
Kaxiras
Efthimios
E
D019281:Dimerization; D004583:Electrons; D007211:Indoles / Q000737:chemistry; D008543:Melanins / Q000737:chemistry* / Q000378:metabolism; D055095:Optics and Photonics; D011522:Protons; D011789:Quantum Theory; D013997:Time Factors
D007211:Indoles; D008543:Melanins; D011522:Protons; C041877:eumelanin; C030374:indole