[60]Fullerene complexes with supramolecular zinc tetraphenylporphyrin assemblies: Synthesis, crystal structures, and optical properties

Different mono-, bi-, and tetradentate N- and O-containing ligands (L) were used in the design of monomer, dimer, and pentamer zinc tetraphenylporphyrin (ZnTPP) assemblies, which then cocrystallized with fullerene C₆₀. Those were pyrazine (1); 4,4′-bipyridyl (2, 8, 9 (with CoTPP)); tetra(4-pyridyl)porphyrin (3); tetrahydrofuran (4); N,N,N′,N′- tetramethyldiaminomethane (5); N,N,N′,N′-tetramethyldiaminoethane (6); N,N,N′,N′-tetramethyldiaminobutene (7); and 1,4-bi-(4,4′-pyridyl)ethylene (10). Molecular structures of new ZnTPP oligomers were described. ZnTPP units, concaved as a result of ligand coordination, effectively cocrystallized with nearly spherical fullerene molecules to produce a variety of packing motifs of fullerenes, namely, three-dimensional (3D) packing in 4, one-dimensional (1D) zigzag chains in 6, a pair arrangement in 1 and 3, and isolated packing in 2. The Zn⋯N(L) bonds were either arranged nearly parallel to the planes of the ligand or bent up to 33° relative to this plane. The characteristic Zn⋯N(L) bond lengths were 2.13-2.21 Å, whereas the Zn⋯C(C₆₀) distances were essentially longer (3.10-3.29 Å). Coordination with ligands and C ₆₀ noticeably shifted the Soret band of ZnTPP to the red side (up to 12 nm) and two Q-bands (up to 26 nm). According to visible-NIR and IR spectra, the complexes had a neutral ground state with charge-transfer bands at 760-820 nm depending on a ZnTPP·L assembly.