The biochar coming from lignin-derived materials upon pyrolysis are widely known due to its remarkable applications as electrodes in different areas such as CO \(_2\) capture, water splitting and energy storage. In this work, the electronic structure properties of lignin are studied at the density functional theory level, with emphasis on geometry optimization and the role played by molecular orbital interactions in shaping absorption spectra. A benchmark study was performed with two functionals widely used in analogous systems to that of a carbonaceous material; namely, B3LYP and \(\omega \) B97X. The results from the benchmark study strongly suggest that the optical properties may be modeled with the B3LYP functional. The geometries of the macromolecular model of lignin and its precursors show significant structural changes from those computed at the ground state that may be interpreted as the beginning of amorphization in pyrolysis processes that triggers the pore formation in lignin-derived biomass. In order to verify the validity of the theoretical results, spectroscopic experiments were performed within the same energy range.
