In order to analyze the spectra of inseparable chemical mixtures, many mathematical methods have been developed to decompose them into the components relevant to species from series of spectral data obtained under different conditions. We formulated a method based on singular value decomposition (SVD) of linear algebra, and applied it to two example systems of organic dyes, being successful in reproducing absorption spectra assignable to cis/trans azocarbazole dyes from the spectral data after photoisomerization and to monomer/dimer of cyanine dyes from those during photodegaradation process. For the example of photoisomerization, polymer films containing the azocarbazole dyes were prepared, which have showed updatable holographic stereogram for real images with high performance. We made continuous monitoring of absorption spectrum after optical excitation and found that their spectral shapes varied slightly after the excitation and during recovery process, of which fact suggested the contribution from a generated photoisomer. Application of the method was successful to identify two spectral components due to trans and cis forms of azocarbazoles. Temporal evolution of their weight factors suggested important roles of long lifetimed cis states in azocarbazole derivatives. We also applied the method to the photodegradation of cyanine dyes doped in DNA-lipid complexes which have shown efficient and durable optical amplification and/or lasing under optical pumping. The same SVD method was successful in the extraction of two spectral components presumably due to monomer and H-type dimer. During the photodegradation process, absorption magnitude gradually decreased due to decomposition of molecules and their decaying rates strongly depended on the spectral components, suggesting that the long persistency of the dyes in DNA-complex related to weak tendency of aggregate formation.
Light-driven supramolecular chiral materials containing an azobenzene moiety as a photoresponsive part and binaphthyl moiety as a chiral part were designed. We found that the dynamic molecular twisting motion of the binaphthyl moiety could be achieved by irradiation of UV or visible light to cause photoisomerization of the azobenzene moiety. The twisting motion induced by the photochromic reaction gave rise to large change in the molecular structure and the value of optical rotation. The chiral materials were demonstrated to behave uniquely as photomodulation of liquid-crystalline helical structures and non-destructive erasable chiroptical memory through photoinduced switching of the dihedral angle of the binaphthyl moiety.
KEYWORDS: Modulation, Ultraviolet radiation, Molecules, Phase shift keying, Liquid crystals, System on a chip, Americium, Molecular machines, Temperature metrology, Absorption
Light- and temperature-driven multistable chiral materials composed of a binaphthyl moiety as a twisting part and an
azobenzene moiety as a photoresponsive part in a single component were investigated. It has been found that the
materials show reversible change in a dihedral angle of the twisting part at various temperatures. In contrast, no change
in the twisting angle of the materials during trans-cis photoisomerization was observed. Furthermore, the chiral
compounds were dissolved in nematic (N) liquid crystals (LCs) to produce a chiral N phase with a helical structure. The
mixture exhibited a dual molecular response to temperature and light. Helical pitch length of the chiral N LC decreased
with increasing temperature because of a molecular twisting motion of the binaphthyl moiety, resulting in a stabilization
of the LC helical structure. On the other hand, length of the helical pitch increased upon photoirradiation, and the
resulting LC mixture was found to show photoswitching between chiral N and N phases upon trans-cis isomerization of
the azobenzene moiety. The photoinduced deformation of the LC helical structure was derived from a bent shape of cis
isomer of the azobenzene moiety in the chiral dopant. This dynamic modulation of the self-organizing helical structure
was based on dual and selective molecular motions of the guest materials induced by external stimuli.
We designed and synthesized a novel type of a cyclic compound containing azobenzene and binaphthyl moieties. The most
significant characteristic of the compound is to possess a reversible change in a dihedral angle of a binaphthyl moiety by
means of photoisomerization of the azobenzene moiety. Furthermore, the compound shows change in a twisting motion in a
solution, a neat film, and a liquid-crystalline host by alternating irradiation of UV and visible light.
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