Organic Electronics from Nature: Investigation of the Electronic and Optical Properties of the Isomers of Bixin and Norbixin Present in the Achiote Seeds

Organic semiconductors have been widely employed in developing new green energy solutions with good cost-efficiency compromise, such as Organic Photovoltaics (OPVs). The light-harvesting process in OPVs is a crucial aspect, which still needs improvements. In this context, the Dye-sensitized solar cells (DSSCs) have arisen as a technically and economically credible alternatives. In this work, we have performed density functional theory (DFT) calculations to investigate the electronic and optical properties of the four natural dyes found in the seeds of annatto (Bixa Orellana L.), which is a natural dye widely found in tropical America. Different DFT functionals, and basis sets, were used in the calculations of the bixin, norbixin, and their trans-isomers (molecules present in Bixa Orellana L.). All molecules present a conjugated backbone with nine double bonds. We observed that the planarity of the molecules and their similar extension for the conjugation pathways provide substantially delocalized wavefunctions of the frontier orbitals and similar values for their energies. Moreover, our findings showed a strong absorption peak in the blue region and the absorption band over the visible spectrum, thus indicating that molecules are good candidates for organic electronic and optoelectronic applications. The results were contrasted with the experimental data.