Optical and electronic properties of monomers of eumelanin: A DFT and TD-DFT computational study

We report a systematic investigation on the electronic and optical properties of four monomers which are elementary constituents of some of the protomolecules of eumelanin. Eumelanin is the most important form of melanin which is one of the most universal natural pigments in living organisms. For the isolated monomers we performed all-electrons Density Functional Theory (DFT) and Time Dependent DFT (TDDFT) calculations with a localized Gaussian basis-set. For each mo-nomer we determined a series of molecular properties, namely electron affinities, ionization energies, fundamental energy-gaps, optical absorption spectra, and exciton binding energies. We discuss moreover the possible implications of the above electronic and optical properties of the single monomers with respect to the properties of a recently proposed tetrameric protomolecule of eumelanin.