title: Unraveling the electronic structure of azolehemiporphyrazines: direct spectroscopic observation of magnetic dipole allowed nature of the lowest π-π* transition of 20π-electron porphyrinoids.
abstract: Hemiporphyrazines are a large family of phthalocyanine analogues in which two isoindoline units are replaced by other rings. Here we report unambiguous identification of 20π-electron structure of triazolehemiporphyrazines (1, 2) and thiazolehemiporphyrazine (3) by means of X-ray analysis, various spectroscopic methods, and density functional theory (DFT) calculations. The hemiporphyrazines were compared in detail with dibenzotetraazaporphyrin (4), a structurally related 18π-electron molecule. X-ray analysis revealed that tetrakis(2,6-dimethylphenyloxy)triazolehemiporphyrazine (1b) adopted planar geometry in the solid state. A weak absorption band with a pronounced vibronic progression, observed for all the hemiporphyrazines, was attributed to the lowest π-π* transition with the electric-dipole-forbidden nature. In the case of intrinsically chiral vanadyl triazolehemiporphyrazine (2), a large dissymmetry (g) factor was detected for the CD signal corresponding to the lowest π-π* transition with the magnetic-dipole-allowed nature. Molecular orbital analysis and NICS calculations showed that the azolehemiporphyrazines have a 20π-electron system with a weak paratropic ring current.
authors.affiliation: Advanced Elements Chemistry Research Team, RIKEN Center for Sustainable Resource Science (CSRS) and Elements Chemistry Laboratory , Wako-shi, Saitama 351-0198, Japan.
authors.forename: Atsuya
authors.initials: A
authors.lastname: Muranaka
authors.forename: Shino
authors.initials: S
authors.lastname: Ohira
authors.forename: Naoyuki
authors.initials: N
authors.lastname: Toriumi
authors.forename: Machiko
authors.initials: M
authors.lastname: Hirayama
authors.forename: Fumiko
authors.initials: F
authors.lastname: Kyotani
authors.forename: Yukie
authors.initials: Y
authors.lastname: Mori
authors.forename: Daisuke
authors.initials: D
authors.lastname: Hashizume
authors.forename: Masanobu
authors.initials: M
authors.lastname: Uchiyama
mesh_terms: D001391:Azo Compounds / Q000737:chemistry*; D001393:Azoles / Q000737:chemistry*; D004583:Electrons; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D011166:Porphyrins / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D001391:Azo Compounds; D001393:Azoles; D011166:Porphyrins