Optical absorption and luminescent properties of melanin films

Complexation in Composite Solutions of Melanin with 2,4,7-Trinitrofluorenone

“…As for our earlier results [4,5], the present studies of the concentration and temperature dependences of melanin PL are in good agreement with the model of the formation of melanin oligomer aggregates with stacking arrangement in a solution. Due to a weak interaction between oligomers in the ground state, they form pre-dimeric structures in the stack.…”

“…The chromatography and elemental analysis have shown that this melanin has a chemical structure similar to that of synthetic melanin based on 5,6-indolequinone monomer [2]. In [4,5], it was stated that 5,6-indolequinone molecules are chemically connected and form polymers or planar two-dimensional molecular oligomers in the form of macromolecular disks, in which chromophores with different lengths of π -π conjugation can be observed. One-dimensional aggregates with stacking arrangement (H-aggregates) can be further formed from two-dimensional oligomers.…”

“…Studied water-soluble melanin has plant origin and was obtained by an extraction [4,5]. The chromatography and elemental analysis have shown that this melanin has a chemical structure similar to that of synthetic melanin based on 5,6-indolequinone monomer [2].…”

“…In our earlier works [4,5], we began the study of a natural melanin pigment absorbing light in a wide spectral range from UV to 1 μm and having semiconductor properties with the optical band gap E g = 1.2 eV. Due to a great number of single and double bonds, the electrons in a melanin macromolecule can easily became free and be excited in a wide spectral range including UV and visible regions.…”

The physical and chemical properties of eumelanin

“…Despite this, several authors have tried to use the absorption spectrum to predict the energy gap in eumelanin assuming an amorphous semiconductor model. For example, Grishchuk et al (2002) tried to extract a solid state gap value for eumelanin films from a Tauc plot [a plot of (aE) 1/2 versus E, where a is the measured absorption coefficient and E is the energy in electron volts]. The slope of the Tauc plot gave an energy gap E g ¼ 1.2 ± 0.2 eV.…”