Mesomeso-linked corrole dimers with modified cores: synthesis, characterization, and properties

Abstract

The synthesis and characterization of the first examples of core-modified corrole dimers linked through the meso positions are described. The dimers are obtained by a simple Ag^I- or Fe^III-catalyzed coupling reaction in near-quantitative yields. The corroles obtained are metalated with metal ions, such as Cu^II and Ni^II. The electronic-absorption spectral studies reveal weak electronic interaction between the two subunits and the exciton coupling observed for the free-base corrole dimer (1717 cm^-1) is lower than that for the corresponding protonated derivative (4081 cm^-1). The solution-state structure derived from ¹H and two-dimensional NMR spectral studies reveals a noncoplanar arrangement of two corrole units. Geometry optimization at the B3LYP-631G level also confirms the noncoplanar arrangement of corroles with a dihedral angle of 64.8° between two corrole planes. The electron paramagnetic resonance (EPR) and magnetic characterization studies on the paramagnetic copper-metalated dimer indicate that both copper ions behave as independent spins without any noticeable interaction. Results of fluorescence studies reveal a bathochromic shift of about 60 nm upon dimerization. The first hyperpolarizability (β) measured by using the hyper Rayleigh scattering (HRS) method reveals doubling of the β values on progressing from monomer to dimer, attributed to enhanced π conjugation. The use of copper dimers in the photocleavage of DNA is also explored. It is shown that the bimetallic copper dimer selectively cleaves the nucleic acids without affecting the proteins, suggesting a possible application of the copper complex in the removal of nucleic acid contaminants from protein extracts through a simple photolytic pathway.