Electrochemical, Spectroelectrochemical, and Structural Studies of Mono- and Diphosphorylated Zinc Porphyrins and Their Self-Assemblies

Three series of porphyrins containing a Zn(II) central metal ion and zero, one, or two phosphoryl groups at the meso-positions of the macrocycle were characterized as to their electrochemical, spectroscopic, and structural properties in nonaqueous media. The investigated compounds are represented as 5,15-bis(4'-R-phenyl)porphyrinatozinc, 10-(diethoxyphosphoryl)-5,15-bis(4'-R-phenyl)porphyrinatozinc, and 5,15-bis(diethoxyphosphoryl)-10,20-bis(4'-R-phenyl)porphyrinatozinc, where R = OMe, Me, H, or CN. Linear-free energy relationships are observed between the measured redox potentials at room temperature and the electronic nature of the substituents at the 5 and 15 meso-phenyl groups of the macrocycle. The mono- and bis-phosphoryl derivatives with two p-cyanophenyl substituents provide electrochemical evidence for aggregation at low temperature, a greater degree of aggregation being observed in the case of 5,15-bis(diethoxyphosphoryl)-10,20-bis(4'-cyanophenyl)porphyrinatozinc(II). This compound was characterized in further detail by variable-temperature ¹H and ³¹P{¹H} NMR spectroscopy in solution combined with single crystal X-ray analysis in the solid state. The data obtained from these measurements indicate that this porphyrin has a dimeric structure in CDCl₃ at 223-323 K but forms a 2D polymeric network when it is crystallized from a CHCl₃/MeOH mixture.