Spectroscopic and Theoretical Studies of Acid–Base Behaviors of N-Confused Porphyrins: Effects of meso-Aryl Substituents.

Theacid–base properties of a series of meso-aryl-substitutedN-confused porphyrins (NCPs) were examined in aqueoussodium dodecyl sulfate (SDS) micellar solutions by both spectrophotometricmethods and theoretical calculations. Reflecting the unsymmetricalstructure of NCP having an outward-pointing pyrrolic nitrogen atom,the first and second protonations were distinguishable in the absorptionand 1H NMR spectra, unlike for porphyrins, and the pK3and pK4valueswere determined discretely. The individual basicities of the NCPswere directly related to the inductive effect of para substituentson the meso-phenyl groups: A linear relationshipbetween the pK3(pK4) and Hammett σparaparameters was revealed.In the case of deprotonation, the structure of monoanionic NCP specieswas similarly characterized by the absorption and 1H NMRspectra. For the second deprotonation, the pK1value was determined to be 11.39 for the NCP derivative withpentafluorophenyl groups. DFT calculations support the changes inelectronic structures and aromaticity of the cationic and anionicspecies. It is demonstrated that NCPs are easily protonated and deprotonatedcompared to the corresponding regular congeners. [ABSTRACT FROM AUTHOR]