title: Spectroscopic and theoretical studies of acid-base behaviors of N-confused porphyrins: effects of meso-aryl substituents.
abstract: The acid-base properties of a series of meso-aryl-substituted N-confused porphyrins (NCPs) were examined in aqueous sodium dodecyl sulfate (SDS) micellar solutions by both spectrophotometric methods and theoretical calculations. Reflecting the unsymmetrical structure of NCP having an outward-pointing pyrrolic nitrogen atom, the first and second protonations were distinguishable in the absorption and (1)H NMR spectra, unlike for porphyrins, and the pK3 and pK4 values were determined discretely. The individual basicities of the NCPs were directly related to the inductive effect of para substituents on the meso-phenyl groups: A linear relationship between the pK3 (pK4) and Hammett σpara parameters was revealed. In the case of deprotonation, the structure of monoanionic NCP species was similarly characterized by the absorption and (1)H NMR spectra. For the second deprotonation, the pK1 value was determined to be 11.39 for the NCP derivative with pentafluorophenyl groups. DFT calculations support the changes in electronic structures and aromaticity of the cationic and anionic species. It is demonstrated that NCPs are easily protonated and deprotonated compared to the corresponding regular congeners.
authors.affiliation: Department of Chemistry and Biochemistry, Graduate School of Engineering, and ‡Education Center for Global Leaders in Molecular Systems for Devices, Kyushu University , 744 Moto-oka, Nishi-ku, Fukuoka 819-0395, Japan.
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Sakashita
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Ishida
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Furuta