title: Chemistry of meso-Aryl-Substituted Expanded Porphyrins: Aromaticity and Molecular Twist.
abstract: Since the discovery of its facile synthesis in 2001, meso-aryl-substituted expanded porphyrins have been developed as a new class of azaannulenes in light of their facile redox interconversions, conformational flexibilities involving flipping of the constitutional pyrroles, rich metal coordination behaviors, unprecedented chemical reactivities, effective platforms to realize versatile electronic states including Möbius aromatic and antiaromatic species, and abilities to stabilize organic radicals. In this Review, the syntheses, structures, and optical, electronic, and magnetic properties of meso-aryl-substituted expanded porphyrins and their metal complexes have been updated with a particular focus on the relationship between "aromaticity and molecular twist (molecular topology)". While the importance of the interplay of these two characteristics has been long recognized from the theoretical viewpoint, meso-aryl-substituted expanded porphyrins offered solid experimental evidence to provide Möbius aromatic and antiaromatic molecules with distinct diatropic and paratropic ring currents, respectively. This attribute is not shared with β-alkylated expanded porphyrin counterparts, underlining the importance and uniqueness of meso-aryl-substituted expanded porphyrins.
authors.affiliation: Department of Chemistry, Graduate School of Science, Kyoto University , Kyoto 606-8501, Japan.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Tanaka
authors.affiliation: Department of Chemistry, Graduate School of Science, Kyoto University , Kyoto 606-8501, Japan.
authors.forename: Atsuhiro
authors.initials: A
authors.lastname: Osuka
mesh_terms: D008968:Molecular Conformation; D011166:Porphyrins / Q000737:chemistry*; D013057:Spectrum Analysis; D014961:X-Ray Diffraction
chemical_list: D011166:Porphyrins