Fig. 4From: Shades of blue: non-invasive spectroscopic investigations of Maya blue pigments. From laboratory mock-ups to Mesoamerican codicesa Computed vertical excitation for monomeric indigo in chloroform. b HOMO and LUMO MO electronic distribution, involved in the transition in the visible region [58]. c HOMO − 1 and LUMO + 1 MO electronic distribution, involved in the main transition in UV regionBack to article page