Azobenzene-bearing
photoswitchable ruthenium catalysts were developed
for olefin metathesis reactions. These catalysts exhibited an on–off
switching ability in ring-closing metathesis depending on UV irradiation
(>99% conversion without UV vs <1% with UV). Photoswitching
phenomena
have been observed in various types of olefin metathesis reactions,
such as ring-opening metathesis, cross-metathesis, and ethenolysis.
The photoswitching feature is also reversible, as the ring-closing
metathesis reaction can repeatedly be turned on and off by switching
the UV light source. Photoisomerization of azobenzene-bearing cyclic(alkyl)(amino)carbene
(azo-CAAC) ligands and the corresponding ruthenium catalysts was observed
by UV–vis spectroscopy.
Grubbs‐type, Hoveyda‐type, cyclic alkyl amino carbene (CAAC)‐based ruthenium olefin metathesis catalysts were used for the acyclic diene metathesis (ADMET) polymerization of 2,7‐divinyl‐9,9‐di‐n‐octylfluorene (DVF). Additionally, various ratios of DVF and 2,2′,7,7′‐tetravinyl‐9,9′‐spirobifluorene (TVSF) were subjected to ADMET polymerization to obtain polymers P1–P7. Polymers P1–P4 were analyzed with gel permeation chromatography, UV–vis spectroscopy, and photoluminescence spectroscopy. As the TVSF ratio increases, polymers exhibit lower solubility but a narrower band in the photoluminescence spectrum. Polymer light‐emitting diode (PLED) devices were fabricated with polymers P1, P2, and P3. The performances of the PLED devices indicated that polymers including more spirobifluorene blocks showed better turn‐on voltage, brightness, current efficiency, and power efficiency.
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