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Control of Chromophore Symmetry by Positional Isomerism of Peripheral Substituents
Author(s) -
Shimizu Soji,
Haseba Yu,
Yamazaki Mariko,
Kumazawa Genji,
Kobayashi Nagao
Publication year - 2014
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201304043
Subject(s) - chromophore , chemistry , crystallography , circular dichroism , conjugated system , molecular symmetry , symmetry (geometry) , structural isomer , spectral line , spectroscopy , singlet state , stereochemistry , photochemistry , molecule , polymer , excited state , physics , atomic physics , geometry , mathematics , organic chemistry , quantum mechanics , astronomy
The first example of the control of porphyrinoid chromophore symmetry based on the positional isomerism of peripheral substituents has been achieved by preparing tetraazaporphyrins (TAPs) with C 4 h , D 2 h , C 2 v , and C s symmetry due to the relative arrangement of peripheral tert ‐butylamino and cyano groups as push and pull substituents, respectively. The four structural isomers were successfully isolated and characterized by 1 H NMR spectroscopy and X‐ray crystallography. The band morphology in the Q‐band region varies depending on the molecular symmetry due to the significant perturbation introduced into the chromophore by the push and pull substituents. The C 4 h and C 2 v isomers exhibit a single Q band, whereas the Q bands of the D 2 h and C s isomers show a marked splitting. The magnetic circular dichroism spectra indicate that the push–pull TAPs retain the properties of the 16‐membered 18π‐electron perimeter generally observed for porphyrinoids. Theoretical calculations have demonstrated that the perturbation introduced by the substituents lowers the D 4 h symmetry of the parent TAP π‐conjugated system, and this results in significant spectral changes. A novel approach to the fine‐tuning of the spectral properties of porphyrinoids based on changes in the chromophore symmetry is described.