Chirality inversion in a molecular exciton

The bichromophoric pigment bilirubin acts as a molecular exciton in its UV- visible and circular dichroism (CD) spectroscopy. The optically active anal ogue, (beta R,beta'R)-dimethyllmesobilirubin-XIII alpha exhibits intense bi signate CD Cotton effects in the region of its long wavelength UV-vis absor ption near 400 nm, with Delta epsilon(434)(max) +337, Delta epsilon(389)(ma x) -186 in the nonpolar solvent CHCl3, and nearly as intense Cotton effects in the polar, hydrogen bonding solvent CH3OH: Delta epsilon(431)(max) +285 , Delta epsilon(386)(max) -177. Addition of amines to Cotton effect sign in versions: in isopropylamine Delta epsilon(436)(max) -605, Delta epsilon(392 )(max) +375, due to an inversion of molecular chirality.