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 (P_I) and its N-methyl (P_II) and N_aN_b-dimethyl (P_III) derivatives by p-nitrophenol is studied by u.v.-visible and i.r. spectroscopy in benzene and dichloromethane. P_I and P_II 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 P_I, 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.