Photoelectronic properties of synthetic melanins

The physical and chemical properties of eumelanin

“…; and secondly, that space charge effects may play a significant role in the rise and decay of photocurrents in addition to trapping and recombination. This view is supported by Rosei et al (1996) who, assuming unipolar transport and a cluster model, suggest that the photoconductive process in eumelanin involves the generation of electron-hole pairs (as per a traditional semiconductor), which subsequently dissociate via thermalization. The dominant competitive processes are trap and geminate recombination (i.e.…”

“…The Rosei et al (1996) study is one of only a handful to address these issues. A number of AC dielectric studies indicate that hopping is the main event in eumelanin charge transport.…”

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

“…All melanins have a series of common structural features that make them similar to organic amorphous semiconductors taking their electronic properties into account. The periodic stacking structure and/or polymeric macromolecular structure with long π -conjugated parts are characteristic features of melanin [2]. Melanins also combine the structural properties of biopolymers and spectral properties of disordered inorganic semiconductors [3].…”

“…Nevertheless, the molecular arrangement of natural melanins is remained vague due to their very complicate structure. It is known that melanin pigments are super-molecular compounds, which are formed at the oxidation of phenols, mainly pyrocatechin, 3,4-dioxyphenylalanine and 5,6-dioxyindole [2]. All melanins have a series of common structural features that make them similar to organic amorphous semiconductors taking their electronic properties into account.…”

Fundamental building blocks of eumelanins: electronic properties of indolequinone-dimers

“…Photoreactivity, ability to bind transition metal ions, redox properties and presence of persistent free radical centers in the pigment structure are usually mentioned as main features of eumelanins [2], although their biological significance is still unclear. X-ray diffraction measurements of dried synthetic pigments have led to a model that pictures eumelanin [7,8,9,10] as a π -stack of crosslinked planar oligomeric structures with a spacing of ≈ 3.4Å. Such a π-conjugated, randomly arranged heteropolymer system could be responsible for intrinsic semiconductivity of eume- lanins [2,6,11,12].…”