Interaction between porphyrins and hydroxylated compounds. Part 1. Study of tetraphenylporphyrin free base and its N-methyl derivatives in the presence of p-nitrophenol
Abstract
The complexation of tetraphenylporphyrin free base (PI) and its N-methyl (PII) and NaNb-dimethyl (PIII) derivatives by p-nitrophenol is studied by u.v.-visible and i.r. spectroscopy in benzene and dichloromethane. PI and PII form a 2:1 and a 1:1 complex, respectively, with p-nitrophenol through intermolecular hydrogen bonding in benzene and an undissociative ion pair in dichloromethane. A study of the porphyrin concentration in the presence of excess of p-nitrophenol shows, in CH2Cl2, a self-association of PI, which is described as the dimerization of the monocomplexed ion-pair species. Equilibrium constants are determined for several complexation reactions as well as for the dimerization process.