Eumelanin is the most common form of the pigment melanin in the human body, with diverse functions including photoprotection, antioxidant behavior, metal chelation, and free radical scavenging. Melanin also plays a role in melanoma skin cancer and Parkinson's disease. Sepia Melanin is a natural eumelanin extracted from the ink sac of cuttlefish.Eumelanin is an ideal candidate to eco-design technologies based on abundant, biosourced and biodegradable organic electronic materials, to alleviate the environmental footprint of the electronics sector.Herein, the focus is on the reversible electrical resistive switching in dry and wet Sepia eumelanin pellets, pointing to the possibility of predominant electronic transport a conditio sine qua non to develop melanin-based electronic devices. These findings shed light on

Over the last decades, the terrific development of consumer electronics, paralleled by a wider access to technology, short device lifetime and replacement cycles, have generated unsustainable amount of waste of...

Melanins (from the Greek μέλας, mélas, black) are bio-pigments ubiquitous in flora and fauna. Eumelanin is an insoluble brown–black type of melanin, found in vertebrates and invertebrates alike, among which Sepia (cuttlefish) is noteworthy. Sepia melanin is a type of bio-sourced eumelanin that can readily be extracted from the ink sac of cuttlefish. Eumelanin features broadband optical absorption, metal-binding affinity and antioxidative and radical-scavenging properties. It is a prototype of benign material for sustainable organic electronics technologies. Here, we report on an electronic conductivity as high as 10 −3 S cm −1 in flexographically printed Sepia melanin films; such values for the conductivity are typical for well-established high-performance organic electronic polymers but quite uncommon for bio-sourced organic materials. Our studies show the potential of bio-sourced materials for emerging electronic technologies with low human- and eco-toxicity.

The integration of the solar energy conversion and electrochemical energy storage functions is critical for limiting the anthropogenic effects on climate change and preventing possible energy shortages related to the increase of the world population. Electrochemical technologies (batteries and supercapacitors) have been investigated to store the energy generated from the Sun, an intermittent source. Abundant, low-cost, non-toxic, potentially biodegradable organic molecular materials, extracted from natural sources, are ideal candidates for applications in sustainable electrochemical energy storage technologies as opposed to those currently used, often based on costly, toxic and scarce elements, thus potentially triggering geopolitical issues. Among natural materials, eumelanin, a ubiquitous biopigment in flora and fauna, stands out for its redox-activity, UV–vis absorption, chemical and thermal stability. This topical review suggests eumelanin as promising sustainable multifunctional material to enhance the electrochemical energy storage properties of organic materials by solar light. The vision behind this research is to pave a way towards the discovery of organic materials and devices that can seamlessly integrate solar energy conversion and storage within the same multifunctional material.

Eumelanin, a macromolecular biopigment, is an attractive candidate for sustainable (green) organic electronics. Establishing structure–property relationships in eumelanin films is an essential step to exploit its technological potential. We report on the evolution from the molecular state to film after spin coating on silicon dioxide solutions of (5,6)-dihydroxyindole (DHI) and (5,6)-dihydroxyindole-2-carboxylic acid (DHICA) eumelanin building blocks (monomers). The evolution of the spin-coated films was studied under various environmental conditions, such as ambient vs an ammonia atmosphere, which catalyzes polymerization. Atomic force microscopy images reveal dramatic morphological changes as a function of the environmental conditions. Infrared and UV–vis spectroscopies indicate that these changes are due to a combination of physical (self-assembly) and chemical (polymerization) processes. Preliminary electrical measurements on films were also carried out.

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BACKGROUND Bio‐sourced (natural) organic materials are often chemically and structurally disordered, such that their structure‐property relationships must be explored using model systems. Eumelanin is an interesting candidate among natural organic materials. RESULTS In this work, the locations of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels of 5,6‐dihydroxyindole (DHI) and 5,6‐dihydroxyindole‐2‐carboxylic acid (DHICA) building blocks (monomers) of the black‐brown biopigment eumelanin, in film form, are studied. The films are fabricated by the spin‐coating technique (i.e., here indicated as DHI‐ and DHICA‐films), which is sometimes followed by ammonia‐induced solid‐state polymerization (i.e., indicated as AISSP‐DHI and AISSP‐DHICA films), as well as by thermal evaporation (i.e., evaporated DHI and DHICA films). From Ultraviolet photoemission spectroscopy (UPS), we deduced the ionization energies (EI) for all DHI‐ and DHICA‐based films to be in the range of 5.34‐5.56 eV and 5.35‐5.80 eV, respectively. The electron affinities (χE) are measurable using inverse photoemission spectroscopy (IPES) for DHI films (3.80 eV) and both evaporated DHI (4.0 eV) and DHICA (3.9 eV) films. On the other hand, the χE values of DHICA, AISSP‐DHI, and AISSP‐DHICA films are estimated with about 0.5 eV of uncertainty. UV‐visible spectroscopy reveals the preferred chromophoric bands for DHICA, AISSP‐DHICA, and DHI are in the range of 300‐330 nm, while AISSP‐DHI exhibits a broadened UV‐visible absorbance. CONCLUSION Our study paves the way for the design of suitable metal‐eumelanin interfaces for electronic applications. © 2021 Society of Chemical Industry (SCI).

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