Integrated computational approach to structural and spectroscopic properties of organic pigments relevant for cultural heritage

An integrated computational approach has been applied to the study of optical and structural properties of alizarin-based pigments. The focus has been on the simulation of electronic spectra line-shapes which can be directly compared with experimental results. In this respect, it has been possible to describe electronic and structural characteristics of free alizarin in different environmental conditions, for which experimental spectroscopic data (UV-Vis) are available, and then extend such studies toward Mg-coordinated alizarin taking into account solvation and coordination effects. It is shown that observed changes of the madder lake color due to such effects are well reproduced by simulations. Such preliminary studies underline the ability of in silico approaches to provide an in-depth comprehension of the nature and composition of original works of art materials, at the same time allowing to understand the physical and chemical changes that occurred over the years affecting both material composition and their chromatic properties, with the description of the factors responsible for the color modifications.