Computational study of the structure of a sepiolite/thioindigo mayan pigment.

The interaction of thioindigo and the phyllosilicate clay sepiolite is investigated using density functional theory (DFT) and molecular orbital theory (MO). The best fit to experimental UV/Vis spectra occurs when a single thioindigo molecule attaches via Van der Waals forces to a tetrahedrally coordinated Al(3+) cation with an additional nearby tetrahedrally coordinated Al(3+) also present. The thioindigo molecule distorts from its planar structure, a behavior consistent with a color change.