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Synthesis and Isomerization Studies of Cyclotrisazobiphenyl
Author(s) -
Reuter Raphael,
Wegner Hermann A.
Publication year - 2011
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.201002671
Subject(s) - photostationary state , isomerization , chemistry , yield (engineering) , photochromism , azobenzene , biphenyl , pyridine , solvent , dimethyl sulfoxide , photochemistry , medicinal chemistry , molecule , organic chemistry , catalysis , photoisomerization , materials science , metallurgy
We report an efficient synthesis of cyclotris[( E )‐3′‐(biphenyl‐3‐yldiazenyl)] compounds (CTBs). An unsubstituted CTB molecule is accessible in four steps in 10 % yield overall, whereas a hexa(methoxymethyl ether) CTB analogue was prepared in nine steps (26 % yield). The final macrocyclization step was accomplished in up to 80 % yield by using a metal‐template effect. Furthermore, the photochromic properties were investigated, and all four isomers were detected and characterized by NMR spectroscopy. A strong influence from the solvent and the irradiation wavelength on the switching process was observed. Irradiation in pyridine yielded the highest amount of the all‐ Z isomer in the photostationary state. For a full conversion to the all‐ E isomer, the reaction has to be heated to 45 °C. The isomerization to the all‐ E isomer is slow at room temperature, with a half‐life time of the all‐ Z isomer of more than nine days in dimethyl sulfoxide (DMSO). Conditions were established to access each possible isomer as the major component in the photostationary state.