Photooptical behavior of a liquid-crystalline dendrimer of the first generation with azobenzene terminal groups (original) (raw)
Related papers
Polymer, 2015
For the first time the influence of molecular structure and generation number of photochromic LC homoand co-dendrimers with azobenzene terminal groups on the photoorientation processes induced by polarized light was studied. It is shown that liquid crystalline smectic or columnar phase formation enables to stabilize photoinduced alignment even at temperatures above the glass transition. Unusual dependence of values of photoinduced dichroism on the generation number was found. For the dendrimers of low generation (1ste3rd) an increase in generation number leads to a decrease in photoinduced dichroism, whereas for the dendrimers of 4th and 5th generation very high values of dichroism were found. These values are comparable with the dichroism for the well-studied before azobenzenecontaining side chain polymers. Possible explanations of the observed peculiarities based on the spectral data, difference in phase behavior and aggregation phenomena are suggested. Possibilities of the optical image photorecording on the films of the photochromic LC-dendrimers were demonstrated.
Chemistry of Materials, 2001
The first photosensitive liquid crystalline (LC) dendrimer with terminal cinnamoyl groups was synthesized. A new approach to the synthesis of photochromic carbosilane LC dendrimers was elaborated. The method consists of synthesis of dendrimer with terminal hydroxyl groups and then coupling of 4-methoxycinnamoyl chloride to it. It was shown that the LC dendrimer of the first generation forms a smectic A (SmA) phase. The photochemical behavior of the dendrimer in dilute solution and in films was studied. The experimental data show that at least two processes, E-Z photoisomerization and [2+2] photocycloaddition leading to the formation of the three-dimensional network, take place. 10.
Chemistry - A European Journal, 2014
A ribbon-shaped chiral liquid crystalline (LC) dendrimer with photochromic azobenzene mesogens and an isosorbide chiral center (abbreviated as AZ 3 DLC) was successfully synthesized and its major phase transitions were studied by using differential scanning calorimetry (DSC) and linear polarized optical microscopy (POM). Its ordered structures at different temperatures were further identified through structure-sensitive diffraction techniques. Based on the experimental results, it was found that the AZ 3 DLC molecule exhibited the low-ordered chiral smectic (Sm*) LC phase with 6.31 nm periodicity at a high-temperature phase region. AZ 3 DLC showed the reversible photoisomerization in both organic solvents and nematic (N) LC media. As a chiralinducing agent, it exhibited a good solubility, a high helicaltwisting power, and a large change in the helical-twisting power due to its photochemical isomerization in the commercially available N LC hosts. Therefore, we were able to reversibly "remote-control" the colors in the whole visible region by finely tuning the helical pitch of the spontaneously formed helical superstructures.
Chemistry - A European Journal, 2004
A series of azobenzene-functionalized poly(alkyl aryl ether) dendrimers have been synthesized and their photochemical and photophysical properties in solution and as thin films have been investigated. Although the photochemical behavior of the azodendrimers in solution indicated that the azobenzene units behave independently , very similar to the constituent monomer azobenzene unit, the properties of thin solid films of the dendrimers were distinctly different. The azoden-drimers, AzoG1, AzoG2, and AzoG3 were observed to form stable supercooled glasses, which showed longwavelength absorption and red emission characteristics of J-aggregates of the azobenzene chromophores. Reversible photoinduced isomerization of the azodendrimers in the glassy state is described.
Synthesis and characterization of termini azobenzene dendrimer
Iranian Chemical Communication, 2013
Some organic molecules can be isomerized upon photoirradiation and when accompanied by a change in the visible absorption spectrum, it is called photochromism. Azobenzenes are important part of molecular machines and nanotechnology, Which are This phenomenon is called photoisomerization Azobenzene (azo) chromophores , and have been incorporated into a wide variety of materials and molecular architectures, including polymers, dendrimers, and molecular glasses. We synthesized and characterized the AB2 type polyamidoamine (PAMAM) dendrimers by single active site. PAMAM diazobenzene dendrimer was synthesized and characterized by FTIR and NMR (1H, 13C) and CHN-O Elementary analysis. The simple method can be used for the synthesis of Azobenzene derivative PAMAM dendrimer and other similar compounds.
Macromolecules, 2007
Upon irradiation with nanosecond pulsed UV laser, surface periodic microstructure and photoorientation occurred simultaneously on the azobenzene functionalized liquid crystalline dendrimer films. The orientation of azo groups was perpendicular to the polarization of pulsed laser and dependent on the laser fluence. The in-plane orientation of azo groups presented parabola-shaped behavior with the increase of laser fluences. The out-of-plane reorientation of azo groups was closely related to thermal effect induced in the procedure of nanosecond pulsed irradiation, which led to the transformation of phase state of azo groups from smectic liquid crystal phase to isotropic phase. Annealing of irradiated film at its liquid crystalline temperature resulted in dramatic enhancement of in-plane orientation and out-of-plane redistribution of azo groups. Liquid crystal alignment on the irradiated film was controlled by a cooperative effect of surface topography and anisotropic molecular orientation simultaneously. Both factors can be modulated by annealing treatment. After annealing, the alignment of liquid crystal molecules can be changed from the direction of surface microgrooves to that of the molecular orientation.