Chelation-enhanced circular dichroism of tripodal bisporphyrin ligands

A chiral tripodal ligand readily prepared from primary amines that contains two monosubstituted tetraphenylporphyrin (TPP) moieties is described. Complexation with Cu(II) in the presence of NH4SCN gives a fully metalated porphyrin and tripoda l ligand complex. The free ligand shows a weak circular dichroism (CD) signal, but metalation gives a strong exciton-coupled CD spectrum. Reduction of the Cu(II) complex results in loss of CD signal.