Unraveling the Electronic Structure of Azolehemiporphyrazines: Direct Spectroscopic Observation of Magnetic Dipole Allowed Nature of the Lowest π–π Transition of 20π-Electron Porphyrinoids

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 sp...

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Published in:The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2014-06, Vol.118 (25), p.4415-4424
Main Authors: Muranaka, Atsuya, Ohira, Shino, Toriumi, Naoyuki, Hirayama, Machiko, Kyotani, Fumiko, Mori, Yukie, Hashizume, Daisuke, Uchiyama, Masanobu
Format: Article
Language:English
Subjects:
Azo Compounds - chemistry
Azoles - chemistry
Density functional theory
Electrons
Magnetic dipoles
Magnetic Resonance Spectroscopy
Mathematical analysis
Molecular Structure
Physical chemistry
Porphyrins - chemistry
Progressions
Quantum Theory
Ring currents
Spectroscopy
X-rays
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Summary: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.
ISSN:1089-5639
1520-5215
DOI:10.1021/jp5001557