We report the synthesis and characterization of a series of novel hexaalkoxydibenz[a,c]anthracenes. While the parent compound is not mesomorphic, the introduction of substituents in the 10- and 13-positions yields compounds with columnar liquid crystalline phases over very broad temperature ranges.
<div>Amorphous metal oxides expand the range of material parameters significantly compared to their crystalline counter parts. However, predictions of the exact nature of the amorphous phase and its effect on material properties are still elusive. Thorough structure-property investigations of well-known model systems are thus necessary before predictive control of useful material properties is obtained. In this work, we fabricate a series of photodeposited nickel (oxy)hydroxide (NiO<sub>x</sub>) thin films and anneal them at temperatures up to 1000 <sup>o</sup>C. EXAFS, XRD and XPS are used to determine the local structure, allowing us to correlate it to measured electrochemical properties. We find an amorphous Ni(OH)<sub>2</sub>-like local structure for annealing conducted below 250 <sup>o</sup>C, followed by an amorphous-to-amorphous phase transition to a NiO-like structure by 300 <sup>o</sup>C, thus supplying evidence for different amorphous polymorphs in this Ni-O system. Above 400 <sup>o</sup>C a cubic NiO XRD diffraction pattern is detected. Electrochemically, we find a stepwise increase of the onset overpotential at this transition, indicating a change in potential-determining step and possibly OER reaction mechanism. The Tafel slope decreases linearly with annealing temperature, which we attribute to a decrease in (Ni)OOH reaction intermediary coverage, supported by <i>in-operando</i> UV-Vis electrochromism. Furthermore, we find that the (Ni)OOH coordination is increasingly strained with annealing temperature, which manifests in higher electrochromic coloring rates and lower binding energies. We identify this as the root cause of the lowered intermediary coverage. Thus, nano-crystalline NiO should kinetically be a superior catalyst to amorphous Ni(OH)<sub>2</sub>. However, at our benchmarking value of 10 mA cm<sup>-2</sup> the amorphous material exhibits lower overpotential, due to a combination of lower onset potential, large chemically active surface area and mass transport limitations under our conditions.</div>
We report the synthesis of a series of 2,3,5,6‐tetraalkoxydibenz[a,c]anthracenes bearing substituents (H, OCH3, or CN) in the 11‐ and 12‐positions and an investigation of their liquid‐crystalline properties. The synthesis involved Suzuki coupling of the appropriate dibromonaphthalene and boronate ester, followed by an oxidative cyclization. Compounds 4 and 5, bearing OCH3 and H, respectively, do not exhibit any liquid‐crystalline properties. In contrast, compounds 6a–c, bearing cyano groups, assemble into columnar mesophases, suggesting that electron‐withdrawing groups are important for promoting columnar mesophase assembly. Analysis of the XRD revealed that compound 6b exhibits a columnar hexagonal phase, whereas compounds 6a and 6c exhibit columnar rectangular phases. The XRD data of 6a and 6b also show reflections that are consistent with antiparallel dimers within the columnar stacks, and intercolumnar spacings suggest that molecules are tilted within the columns.
Amorphous metal oxides expand the range of material parameters significantly compared to their crystalline counter parts. However, predictions of the exact nature of the amorphous phase and its effect on material properties are still elusive. Thorough structureproperty investigations of well-known model systems are thus necessary before predictive control of useful material properties is obtained. In this work, we fabricate a series of photodeposited nickel (oxy)hydroxide (NiO x ) thin films and anneal them at temperatures up to 1000 • C. EXAFS, XRD and XPS are used to determine the local structure, allowing us to correlate it to measured electrochemical properties. We find an amorphous Ni(OH) 2 -like local structure for annealing conducted below 250 • C, followed by an amorphous-to-amorphous phase transition to a NiO-like structure by 300 • C, thus supplying evidence for different 1 amorphous polymorphs in this Ni-O system. Above 400 • C a cubic NiO XRD diffraction pattern is detected. Electrochemically, we find a stepwise increase of the onset overpotential at this transition, indicating a change in potential-determining step and possibly OER reaction mechanism. The Tafel slope decreases linearly with annealing temperature, which we attribute to a decrease in (Ni)OOH reaction intermediary coverage, supported by in-operando UV-Vis electrochromism. Furthermore, we find that the (Ni)OOH coordination is increasingly strained with annealing temperature, which manifests in higher electrochromic coloring rates and lower binding energies. We identify this as the root cause of the lowered intermediary coverage. Thus, nano-crystalline NiO should kinetically be a superior catalyst to amorphous Ni(OH) 2 . However, at our benchmarking value of 10 mA cm −2 the amorphous material exhibits lower overpotential, due to a combination of lower onset potential, large chemically active surface area and mass transport limitations under our conditions.
The ability to form self-organized thermotropic mesophases of amphiphilic cyclodextrins correlates well with their ability to establish an intermolecular H-bond network.
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