Charge separation in metallomacrocycle complexes linked with electron acceptors by axial coordination

Abstract

A simple but elegant way to obtain linked donor–acceptor entities involving metallomacrocycle complexes with fixed distance and orientation is the use of coordination of axial ligands to metallomacrocycle complexes. A series of electron acceptor-bearing silicon phthalocyanine (SiPc) triads have been readily synthesized, using the six-coordinated nature of the central silicon atom, by attachment of two electron-acceptor units, fullerene SiPc-(C₆₀)₂, trinitrofluorenone SiPc-(TNF)₂ and trinitrodicyanomethylenefluorene SiPc-(TNDCF)₂. The nitrogen of pyridylnaphthalenediimide (PyNIm) can coordinate to the metal center of zinc porphyrin to form a donor–acceptor complexes: ZnTPP-PyNIm. The binding of pyridine moieties to Zn-porphyrin complexes is much enhanced by the distortion of porphyrin ring. By taking advantage of saddle distortion of zinc octaphenylphthalocyanine (ZnOPPc) and diprotonated dodecaphenylporphyrin (H₄DPP²⁺), a discrete supramolecular assembly composed of Zn(OPPc) and H₄DPP²⁺ and is obtained by using 4-pyridinecarboxylate (4-PyCOO⁻) with the axial coordination bond and hydrogen bonding. The charge separation in these metal macrocycles linked with electron acceptors with axial coordination bonds is described together with the application to develop supramolecular solar cells.