(Invited) Biodegradable Organic Electronics: Degradation of Eumelanin Studied by Fluorescence Spectroscopy

Abstract

A paradigm shift in resource exploitation and e-waste management is needed to promote sustainability in electronics. Reusing and recycling electronic devices is not only environmentally desirable but also economically viable and increasingly socially acceptable. A promising route to alleviate the environmental footprint of electronics is based on the use of abundant materials, novel production schemes involving non-toxic materials (through green chemistry processes), and eco-design of devices that includes environmentally acceptable end-of-life scenarios. Within this context, we integrate biosourced electro- and photo-active organic electronic materials, such as melanin, indigo, tannin and lignin derivatives (some of these readily available from biomass feedstock, abundant in Canada) into electronic and energy storage devices, such as transistors andbatteries. Biosourced organic electronic materials can be biodegradable. As such, they offer the opportunity for an environmentally benign device end-of-life scenario (as opposed to the present accumulation of e-waste).The melanin biopigment family serves as a prototypical environmentally benign class of materials for sustainable organic electronics and its powering elements. Among melanins, eumelanin is a brown-black type found in the human body, other mammals, reptiles, amphibians, and fishes as well as in invertebrates, such as cuttlefish and insects. Sepia Melanin (natural eumelanin) is a type of biosourced eumelanin extracted from the ink sac of cuttlefish. Synthetic eumelanin is commercially available (indicated here as Sigma eumelanin).We recently reported on encouraging studies on the biodegradability of eumelanin in industrial compost conditions (Di Mauro, E., Rho, D. & Santato, C. Biodegradation of bio-sourced and synthetic organic electronic materials towards green organic electronics. Nature Communications, https://doi.org/10.1038/s41467-021-23227-4); unfortunately, we did not report on intermediates of the biodegradation process. Insight on intermediates is expected to bring about an increase of the mineralization rate of eumelanin. Here, we will discuss possible oxidative degradation pathways of the biopigment eumelanin tin industrial compost conditions hrough fluorescence spectroscopy. Indeed, literature reports that oxidized (by oxidative cleavage of the quinoid structure of the indole moiety), naturally occurring eumelanin can give a lipofuscin-like yellow fluorescence.