Chelation-Enhanced Circular Dichroism of Tripodal Bisporphyrin Ligands

摘要

Porphyrins are superb chromophores that offer well-defined metal binding sites rich with reaction and molecular recognition chemistry. The photochemical behavior of porphyrins has played an important role in studies of artificial photosynthesis, photoreduction, photodynamic therapy, sensors, optical materials, and much more. Circular dichroism (CD) has become a versatile tool for configu-rational assignment and the structural evaluation of chiral porphyrins and phthalocyanines. In particular, exciton coupled circular dichroism (ECCD) has become the spectral method of choice for configurational assignment of chiral substrates containing dichroic chromophores due to its non-empirical theoretical foundation. We have utilized this method and demonstrated such an approach with quinoline-derivatized chiral amino acids, primary amines, and alcohols. Additionally, we have used ECCD to characterize redox-responsive coordination complexes of interest as optical materials. Here we report a chiral tripodal ligand readily prepared from primary amines that contains two monosubstituted tetraphen-ylporphyrin (TPP) moieties and show that chelation of Cu(II) results in strong ECCD spectra with visible wavelength light.