title: Tetrabenzoporphyrin and -mono-, -cis-di- and Tetrabenzotriazaporphyrin Derivatives: Electrochemical and Spectroscopic Implications of meso CH Group Replacement with Nitrogen.
abstract: Nonperipherally hexyl-substituted metal-free tetrabenzoporphyrin (2H-TBP, 1a) tetrabenzomonoazaporphyrin (2H-TBMAP, 2a), tetrabenzo-cis-diazaporphyrin (2H-TBDAP, 3a), tetrabenzotriazaporphyrin (2H-TBTAP, 4a), and phthalocyanine (2H-Pc, 5a), as well as their copper complexes (1b-5b), were synthesized. As the number of meso nitrogen atoms increases from zero to four, λmax of the Q-band absorption peak becomes red-shifted by almost 100 nm, and extinction coefficients increased at least threefold. Simultaneously the blue-shifted Soret (UV) band substantially decreased in intensity. These changes were related to the relative electron-density of each macrocycle expressed as the group electronegativity sum of all meso N and CH atom groups, ∑χR. X-ray photoelectron spectroscopy differentiated between the three different types of macrocyclic nitrogen atoms (the Ninner, (NH)inner, and Nmeso) in the metal-free complexes. Binding energies of the Nmeso and Ninner,Cu atoms in copper chelates could not be resolved. Copper insertion lowered especially the cathodic redox potentials, while all four observed redox processes occurred at larger potentials as the number of meso nitrogens increased. Computational chemical methods using density functional theory confirmed 1b to exhibit a Cu(II) reduction prior to ring-based reductions, while for 2b, Cu(II) reduction is the first reductive step only if the nonperipheral substituents are hydrogen. When they are methyl groups, it is the second reduction process; when they are ethyl, propyl, or hexyl, it becomes the third reductive process. Spectro-electrochemical measurements showed redox processes were associated with a substantial change in intensity of at least two main absorbances (the Q and Soret bands) in the UV spectra of these compounds.
authors.affiliation: †Department of Chemistry, University of the Free State, Bloemfontein 9300, South Africa.
authors.forename: Adele
authors.initials: A
authors.lastname: van As
authors.affiliation: †Department of Chemistry, University of the Free State, Bloemfontein 9300, South Africa.
authors.forename: Chris C
authors.initials: CC
authors.lastname: Joubert
authors.affiliation: †Department of Chemistry, University of the Free State, Bloemfontein 9300, South Africa.
authors.forename: Blenerhassitt E
authors.initials: BE
authors.lastname: Buitendach
authors.affiliation: †Department of Chemistry, University of the Free State, Bloemfontein 9300, South Africa.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Erasmus
authors.affiliation: †Department of Chemistry, University of the Free State, Bloemfontein 9300, South Africa.
authors.forename: Jeanet
authors.initials: J
authors.lastname: Conradie
authors.affiliation: ‡School of Chemistry, University of East Anglia, Norwich NR4 7TJ, United Kingdom.
authors.forename: Andrew N
authors.initials: AN
authors.lastname: Cammidge
authors.affiliation: ‡School of Chemistry, University of East Anglia, Norwich NR4 7TJ, United Kingdom.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Chambrier
authors.affiliation: ‡School of Chemistry, University of East Anglia, Norwich NR4 7TJ, United Kingdom.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Cook
authors.affiliation: †Department of Chemistry, University of the Free State, Bloemfontein 9300, South Africa.
authors.forename: Jannie C
authors.initials: JC
authors.lastname: Swarts
mesh_terms: D001555:Benzene Derivatives / Q000737:chemistry*; D056831:Coordination Complexes / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D055664:Electrochemical Techniques; D007211:Indoles / Q000737:chemistry*; D054833:Isoindoles; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D009584:Nitrogen / Q000737:chemistry*; D056951:Photoelectron Spectroscopy; D011166:Porphyrins / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet
chemical_list: D001555:Benzene Derivatives; D056831:Coordination Complexes; D007211:Indoles; D054833:Isoindoles; D011166:Porphyrins; D003300:Copper; D009584:Nitrogen; C013647:phthalocyanine