Multi-expanded porphyrin assemblies on cyclophosphazene scaffolds

Abstract

Cyclotriphosphazene and cyclotetraphosphazene appended with six and eight sapphyrin units, respectively, were prepared by treating N₃P₃Cl₆ and N₄P₄Cl₈ with the appropriate equivalents of 5,10,15-tri(p-tolyl)-20-(4-hydroxyphenyl)-25,27,29-trithiasapphyrin in tetrahydrofuran (THF) in the presence of Cs₂CO₃ at temperatures of 0 to 60 °C for 8–12 h. The two multi-expanded porphyrin assemblies were soluble in common organic solvents, and their identities were confirmed by their corresponding molecular ion peak in the MALDI-TOF mass spectra. 1D and 2D NMR spectroscopic techniques were used to deduce the molecular structures of the mult-expanded porphyrin assemblies. Absorption spectral studies showed that the band positions of the multisapphyrin assemblies were similar to that of the monomeric sapphyrin, but the extinction coefficients were three- to four-fold higher than that of the monomeric sapphyrin. The multisapphyrin assemblies are not very stable under redox conditions.