ARYLOXO DERIVATIVES OF PHOSPHORUS(V) PORPHYRINS - SYNTHESIS, SPECTROSCOPY, ELECTROCHEMISTRY, AND SINGLET-STATE PROPERTIES

Aryloxo derivatives of phosphorus(V) porphyrins of the type [(TpTP)P(O R)(2)](OH-)-O-+ where TpTP is the dianion of tetra-p-tolylporphyrin an d OR is an axial aryloxo (2,4-dimethylphenoxo, 4-methylphenoxo, phenox o, 4-nitrophenoxo, 4-(4-nitrophenoxy)phenoxo, or 4-(2,4-dinitrophenoxy )phenoxo) ligand have been synthesized and fully characterized by FAB- mass, W-vis, fluorescence, infrared, and nuclear magnetic resonance (H -1 and P-31) spectroscopies and cyclic voltammetric methods. Each new porphyrin shows a typical ''normal UV-vis absorption spectrum'' indica ting the presence of a P(V) ion in the porphyrin cavity. The proton-de coupled P-31 NMR signal observed for these compounds, between -194 and -200 ppm, suggests that there exists an octahedral coordination aroun d the phosphorus atom, and this supposition is further substantiated b y the porphyrin ring-current-induced upfield shifts observed for proto ns on the two axial aryloxo ligands in the H-1 NMR spectra. Cyclic vol tammetric studies reveal that each porphyrin undergoes two successive, one-electron reductions with the site of electron transfer being the porphyrin ring. The fluorescence quantum yield values of these porphyr ins are found to be sensitive to the nature of the aryloxo ligand and also to the solvent polarity. The singlet state properties of these sy stems have been discussed in light of both the fluorescence and the re dox potential data.