Excitonic effects from geometric order and disorder explain broadband optical absorption in eumelanin

Chun-Teh Chen, Chern Chuang, Jianshu Cao, Vincent Ball, David Ruch and Markus J. Buehler ()
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Chun-Teh Chen: Laboratory for Atomistic and Molecular Mechanics (LAMM), Massachusetts Institute of Technology
Chern Chuang: Massachusetts Institute of Technology
Jianshu Cao: Massachusetts Institute of Technology
Vincent Ball: Faculté de Chirurgie Dentaire, Université de Strasbourg, 8 rue Sainte Elizabeth, 67000 Strasbourg, France and Unité INSERM 1121
David Ruch: Centre de Recherche Public Henri Tudor
Markus J. Buehler: Laboratory for Atomistic and Molecular Mechanics (LAMM), Massachusetts Institute of Technology

Nature Communications, 2014, vol. 5, issue 1, 1-10

Abstract: Abstract Eumelanin is a ubiquitous biological pigment, and the origin of its broadband absorption spectrum has long been a topic of scientific debate. Here, we report a first-principles computational investigation to explain its broadband absorption feature. These computations are complemented by experimental results showing a broadening of the absorption spectra of dopamine solutions upon their oxidation. We consider a variety of eumelanin molecular structures supported by experiments or theoretical studies, and calculate the absorption spectra with proper account of the excitonic couplings based on the Frenkel exciton model. The interplay of geometric order and disorder of eumelanin aggregate structures broadens the absorption spectrum and gives rise to a relative enhancement of absorption intensity at the higher-energy end, proportional to the cube of absorption energy. These findings show that the geometric disorder model is as able as the chemical disorder model, and complements this model, to describe the optical properties of eumelanin.

Date: 2014
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Persistent link: https://EconPapers.repec.org/RePEc:nat:natcom:v:5:y:2014:i:1:d:10.1038_ncomms4859

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DOI: 10.1038/ncomms4859

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