Photoisomerizable Metallomesogens and Soft Crystals Based on Orthopalladated Complexes

Abstract

With the aim of obtaining light-responsive liquid-crystalline palladium complexes, six palladium complexes derived from an orthometalated imine, bearing one or two azocarboxylato bridges, have been synthesized: [Pd(2)(μ-SC(10)H(21))(μ-O(2)CAzo)(L(1,2))(2)] (7 and 8), [Pd(2)(μ-SC(10)H(21))(μ-O(2)CAzo3C(10))(L(1,2))(2)] (9 and 10), [Pd(μ-O(2)CAzo)L(1)](2) (11), and [Pd(μ-O(2)CAzo3C(10))L(1)](2) (12), in which L(1) = p-H(21)C(10)OC(6)H(3)CH═NC(6)H(4)OC(10)H(21)-p, L(2) = p-H(21)C(10)OC(6)H(3)CH═NC(14)H(29), AzoCO(2)(-) = p-(phenylazo)benzoate, and Azo3C(10)CO(2)(-) = p-(2',3',4'-tris-n-decyloxyphenylazo)benzoate. Three of them (7-9), as well as the precursor Azo3C(10)CO(2)H (3), are thermotropic liquid crystals displaying nematic and smectic A mesophases, while 10-12 have been identified by X-ray diffraction to give rise to "soft" crystal phases. Electronic spectroscopy and (1)H NMR show that all of them undergo a trans-cis isomerization of the azobenzene moiety at λ = 365 nm. The molecular structure determines the photoresponse in solution, which is faster and more stable when the trisubstituted azocarboxylate is present and the motion of the azo group is not hindered by the orthometalated imine. The photoresponse has also been observed in the condensed phases, which change from the ordered phase to the isotropic liquid upon irradiation, except for compound 10, a soft crystal in which a permanent photoalignment highly sensitive to light polarization is produced. The latter is a behavior with potential applications, rather unusual in low-molecular-weight compounds.

Nanoporous Films with Photoswitchable Absorption Kinetics Based on Polymerizable Columnar Discotic Liquid Crystals

“…First, ethyl 4-aminobenzoate was diazotized with sodium nitrite to give the corresponding diazonium salt. The azo product, 4-((3,4,5-trihydroxyphenyl)­diazenyl)­benzoate ( 1 ), was obtained by reacting the freshly prepared diazonium salt with 1,2,3-tris­(hydroxybenzene) (pyrogallol) .…”

“…The azo product, 4-((3,4,5-trihydroxyphenyl)diazenyl)benzoate (1), was obtained by reacting the freshly prepared diazonium salt with 1,2,3-tris(hydroxybenzene) (pyrogallol). 26 1 H nuclear magnetic resonance (NMR) showed that substitution predominantly took place at the 4-position of pyrogallol due to the electron-donating nature of the hydroxy groups, favoring substitution at the ortho and para positions. 27 Alkylation of the phenolic hydroxy groups with 11-bromo-1-undecene yielded tris-alkene ester 2, which was hydrolyzed with aqueous potassium hydroxide, followed by acidification with aqueous hydrochloric acid to give photoswitchable acid Azoac.…”

Loss of heterozygosity at 9q32–33 (DBC1 locus) in primary non‐invasive papillary urothelial neoplasm of low malignant potential and low‐grade urothelial carcinoma of the bladder and their associated normal urothelium

“…Actually, photo‐induced isothermal phase transitions in macroscopic order by azobenzene derivatives have been investigated for liquid crystalline to isotropic phase transition,1 crystal to isotropic phase transition,2 fluidity change in Langmuir films,3 and sol‐gel transition 4. However, photoisomerization of azobenzene is basically difficult in highly ordered crystalline solids owing to insufficient free volume; only a limited number of examples have been reported in specific conditions, such as soft crystals,5 micro crystals,6 crystal surfaces,7 nanosized crystals,8 and crystalline cyclic molecules 2. In addition, transition from a solid to a fluidic liquid with photoisomerization has rarely been reported, even in a photoisomerizable glassy solid or polymer matrices 9.…”

Photoreversible Micellar Solution as a Smart Drag-Reducing Fluid for Use in District Heating/Cooling Systems

“…It should be noted that peak 2 is significantly lower and that peak 3 grows slightly. The changes in spectra correspond to the isomerization of trans- ACA to cis -ACA. , The UV-irradiated solution was then irradiated by visible light. The resulting spectrum is essentially the same as the fresh spectrum, indicating that cis -ACA reverted to trans- ACA.…”