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Shape‐Switchable Azo‐Macrocycles
Author(s) -
Müri Marcel,
Schuermann Klaus C.,
De Cola Luisa,
Mayor Marcel
Publication year - 2009
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200801282
Subject(s) - chemistry , photoisomerization , terphenyl , photostationary state , azo coupling , vapor pressure osmometry , coupling reaction , polymer chemistry , isomerization , photochemistry , stereochemistry , organic chemistry , vapor pressure , catalysis
The synthesis of four shape‐switchable macrocycles comprising different peripheral substituents is described. The macrocycles 1 – 4 consist of m ‐terphenyl semicircles interlinked by two azo joints. These macrocycles were assembled from nitro‐functionalized m ‐terphenyl moieties through reductive dimerization. The semicircles were assembled through Suzuki cross‐coupling reactions. The molecular weights of the macrocycles were determined by vapour pressure osmometry, because mass spectrometry failed in the cases of 2 and 3 . The E → Z photoisomerization reactions were analysed by UV/Vis spectroscopy complemented by 1 H NMR studies. A very slow thermal back‐reaction indicated considerable stabilization of the Z isomer. The reduced efficiency of the thermal back‐reaction probably arises from the reduced degree of freedom due to the mechanical interlinking of the two azo groups. The photostationary state consisted of all‐ Z (85 %) and all‐ E isomers (15 %). The E → Z transformation induced by irradiation displayed simple exponential kinetics, which indicates pairwise switching of the two azo groups in a macrocycle, at least on the timescale under investigation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)