Photoinduced electron transfer in supramolecular assemblies involving saddle-distorted porphyrins and phthalocyanines

Unique supramolecular assemblies are constructed based on a saddle-distorted non-planar porphyrin, dodecaphenylporphyrin (H₂DPP), and its metal complexes. The saddle distortion facilitates protonation of pyrrole nitrogens to afford a stable diprotonated porphyrin, which can act as an electron acceptor. A diprotonated hydrochloride salt of a saddle-distorted dodecaphenylporphyrin ([H₄DPP]Cl₂) forms a nano-sized channel structure called a "porphyrin nanochannel". Electron-donating molecules such as hydroquinones are included as guest molecules in the porphyrin nanochannel. Photoinduced electron transfer from the guest molecules to the singlet state of H₄DPP²⁺ occurs, producing H ₄DPP^+• and cation radicals of the guest molecules. The saddle distortion also results in higher Lewis acidity at a metal center to maintain axial coordination of ligands, due to poor overlap of the lone-pair orbitals with the d orbitals of the metal center. By taking advantage of saddle distortion of both H₄DPP²⁺ and zinc phthalocyanine, 1,4,8,11,15,18,22,25-octaphenylphthalocyanine (ZnOPPc), a discrete supramolecular assembly composed of H₄DPP²⁺ and ZnOPPc, is obtained using 4-pyridinecarboxylate (4-PyCOO^-) that connects the two components by hydrogen bonding and coordination bonding, respectively. Photoexcitation of the assembly results in efficient electron transfer from ZnOPPc to H₄DPP²⁺ in the supramolecular complex.