Eumelanin is a chemically and structurally disordered biomacromolecule ubiquitous in flora and fauna and a promising candidate for green electronics. Its disorder implies that its electronic properties, e.g. the location of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels can be clearly established only by using model (chemically controlled) systems.<br/>In this work, we deposited films of chemically controlled eumelanin by two routes: solution-processing and vacuum thermal evaporation, from powders of eumelanin building blocks (5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA)). We carried out solution processing by spin-coating, possibly followed by ammonia exposure to induce solid-state polymerization. The ionization energies obtained by ultraviolet photoemission spectroscopy (UPS) were in the ranges of 5.3-5.6 eV and 5.4-5.8 eV, for DHI- and DHICA-based thin films, respectively. The electron affinities measured by inverse photoemission spectroscopy (IPES) were 3.8 eV for spin coated DHI films, 4.0 eV for evaporated DHI films and 3.9 eV for evaporated DHICA films. The IPES measurement of samples exposed to ammonia (polymerized samples) was challenging, and an error of about 0.5 eV was associated with the measurement. Our UPS, IPES study has the potential to pave the way for the design of optimized metal-eumelanin interfaces for green organic electronic applications.

Eumelanin biopigment: thin-film fabrication and location of the HOMO and LUMO levels by UPS and IPES

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.