Abstract
A series of polymers containing nunchaku-like unit with an azo chromophore and a mesogen group was successfully prepared and photoinduced anisotropy of the obtained polymers was minutely investigated. Firstly, monomers containing nunchaku-like unit with an azo chromophore and a mesogen group linked by flexible group were synthesized. The structure of the monomers was confirmed via NMR COSY spectra. Subsequently, the obtained monomers were polymerized into corresponding polymers through RAFT polymerization. The prepared polymer samples were characterized through NMR, FTIR, gel permeation chromatography (GPC), and UV-vis testing while the thermal properties of the samples were investigated through differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA) measurements. The photoinduced isomerization of the polymers, which was researched in situ via measuring UV-vis spectra of the polymer solutions and spin-coated films under irradiation with 450 nm light or putting in darkness, demonstrated the rapid trans-cis-trans isomerization of the polymers. When irradiated with a linearly polarized light, significant photoinduced birefringence and dichroism were observed, suggesting photoinduced isomerization of azobenzene can drive orientation of mesogen in the system. This study blazes a way to design the optical materials with light-controllable birefringence and dichroism.
Highlights
Azobenzene, which can perform trans-cis isomerization upon irradiating with suitable light, has been intensively investigated as photoresponsive materials [1,2,3,4]
To further improve the photoinduced anisotropy of the pseudo-stilbene azobenzenes, liquid crystalline mesogens are designed to be linked with the azobenzene chromophores
A series of polymers (8A, 8B, and 8C) containing nunchaku-like unit with an azobenzene and a mesogen was polymerized from monomers (7A, 7B, and 7C) containing nunchaku-like unit with an mesogen was polymerized from monomers (7A, 7B, and 7C) containing nunchaku-like unit with an azobenzene and a mesogen linked by flexible group which were synthesized through a seven-step azobenzene and a mesogen linked by flexible group which were synthesized through a seven-step procedure
Summary
Azobenzene, which can perform trans-cis isomerization upon irradiating with suitable light, has been intensively investigated as photoresponsive materials [1,2,3,4]. Liquid crystals which usually contain rod-like mesogens can exhibit giant dichroism and birefringence when oriented [19,20]. Due to the mesogenic property of azobenzene, the azobenzene branch usually displays liquid crystalline features [23,24,25,26]. As a consequence, such kind of azobenzene tends to exhibit higher photoinduced anisotropy when exposed to polarized light. To further improve the photoinduced anisotropy of the pseudo-stilbene azobenzenes, liquid crystalline mesogens are designed to be linked with the azobenzene chromophores. The obtained molecules exhibiting the properties of azo molecular glasses display significant photoinduced birefringence and dichroism. The photoinduced dichroism and birefringence of these polymers are studied minutely
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