Advanced polyimide materials: Syntheses, physical properties and applications

Synthetic organic chemists enjoy the luxury of having a large collection of reliable reactions at their disposal for preparing small molecules, mesoscopic structures, and polymers. Coordination chemists, on the other hand, are faced with the fact that transition metal chemistry, when normalized for the number of transition metals, has relatively few high-yielding reactions, when compared to the chemistry of carbon, for preparing even small molecule structures. This lack of control is manifested, in large part, in the weak metal-ligand interactions found in coordination complexes as compared with the strong covalent bonds in organic compounds. Weak bonding often translates into many reaction pathways that are not substantially different from an energetic point of view, and therefore, results in poor selectivity. As a result, many coordination chemists in recent years have come to the realization that it may be easier and more productive to develop straightforward and reliable routes to mesoscopic supramolecular structures by capitalizing on the modest collection of high-yielding reactions in coordination chemistry, the directional bonding afforded by metal centers, and strategies aimed at taking advantage of the weak metal bonds found in coordination complexes. Three emerging synthetic strategies, the symmetry-interaction, directional-bonding, and weak-link synthetic approaches, all use metal centers as structural building blocks to rationally assemble molecular components into supramolecular metallocyclophanes. These three approaches are discussed herein, and the fundamental principles underlying each as well as their capabilities are compared and contrasted.

Strategies for the Construction of Supramolecular Compounds through Coordination Chemistry

http://nathan.instras.com/MyDocsDB/doc-617.pdf

Electrochromic organic and polymeric materials for display applications

Short-term transients, including those related to wind and solar sources, present challenges to the electrical grid. Stationary energy storage systems that can operate for many cycles, at high power, with high round-trip energy efficiency, and at low cost are required. Existing energy storage technologies cannot satisfy these requirements. Here we show that crystalline nanoparticles of copper hexacyanoferrate, which has an ultra-low strain open framework structure, can be operated as a battery electrode in inexpensive aqueous electrolytes. After 40,000 deep discharge cycles at a 17 C rate, 83% of the original capacity of copper hexacyanoferrate is retained. Even at a very high cycling rate of 83 C, two thirds of its maximum discharge capacity is observed. At modest current densities, round-trip energy efficiencies of 99% can be achieved. The low-cost, scalable, room-temperature co-precipitation synthesis and excellent electrode performance of copper hexacyanoferrate make it attractive for large-scale energy storage systems.

/pdf/copper-hexacyanoferrate-battery-electrodes-with-long-cycle-342zxyaxnu.pdf

Copper hexacyanoferrate battery electrodes with long cycle life and high power

Some animals, such as the chameleon and cephalopod, have the remarkable capability to change their skin colour. This unique characteristic has long inspired scientists to develop materials and devices to mimic such a function. However, it requires the complex integration of stretchability, colour-changing and tactile sensing. Here we show an all-solution processed chameleon-inspired stretchable electronic skin (e-skin), in which the e-skin colour can easily be controlled through varying the applied pressure along with the applied pressure duration. As such, the e-skin's colour change can also be in turn utilized to distinguish the pressure applied. The integration of the stretchable, highly tunable resistive pressure sensor and the fully stretchable organic electrochromic device enables the demonstration of a stretchable electrochromically active e-skin with tactile-sensing control. This system will have wide range applications such as interactive wearable devices, artificial prosthetics and smart robots.

/pdf/a-chameleon-inspired-stretchable-electronic-skin-with-3f5qi8fw6v.pdf

A chameleon-inspired stretchable electronic skin with interactive colour changing controlled by tactile sensing

A number of inorganic and organic materials exhibit redox states (reduced and/or oxidised forms) with distinct UV-Visible (electronic) absorption bands. When electrochemical switching of these redox states gives rise to different colours (i.e. new or different visible region bands), the material is described as being electrochromic. By virtue of their numerous applications, both of academic and commercial interest, electrochromic materials are currently attracting a great deal of interest. This review provides an introduction to the major classes of electrochromic materials, namely transition metal oxides, Prussian blue systems, viologens, conducting polymers, transition metal and lanthanide coordination complexes and metallopolymers, and metal phthalocyanines. Examples of some new materials and of prototype and commercial electrochromic devices are cited.

/pdf/new-electrochromic-materials-2sst279q56.pdf

New Electrochromic Materials

Synthesis, Photochemistry, and Molecular Structures of Peripherally-Molybdenated Tetraphenylporphyrins and -metalloporphyrins

A new donor–acceptor (D–A) molecule, 5,10,15,20-[N-benzyl-N′-(4-benzyl-4,4′-bipyridinium-4-pyridyl)]triphenylporphyrin
 tris(hexafluorophosphate), 4, has been synthesised. The diad, 4, and its precursors, have been fully characterised by 1H and 13C NMR spectroscopy, mass spectrometry, UV/Visible spectroscopy and cyclic voltammetry.
 In-situ UV/Visible and EPR measurements show that the site of the first electrochemical reduction is the benzylviologen component of the molecule. The second reduction wave from cyclic voltammetry was shown by in-situ EPR to comprise two unresolved one-electron processes, and this was confirmed by chronocoulometry. The first of these two reduction processes rendered the diad diamagnetic, as was shown by the disappearance of the signal due
 to the benzylviologen radical. The second gave rise to the appearance of a new EPR signal, which was found to
 correspond to the porphyrin radical. We
 believe this
 to be the first reported resolved spectrum of a monoreduced porphyrin radical.

Synthesis, electrochemistry and spectroelectrochemistry of a porphyrin–viologen donor–acceptor diad

The para, meta, and ortho peripherally-molybdenated tetraphenylporphyrin complexes [5-{[Mo(NO)Tp*Cl]NHC6H4}-10,15,20-Ph3porphH2] [1−3, respectively; Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate; Ph3porphH2 = triphenylporphyrin] have been prepared by reaction of the corresponding 5-(aminophenyl)-10,15,20-triphenylporphyrin derivative with [Mo(NO)Tp*Cl2]. Cyclic voltammetry shows that most of these complexes undergo two oxidation processes (associated with the porphyrin) and three reduction processes (two associated with the porphyrin, and one with the molybdenum fragment). The redox potentials of the molybdenum fragment are little influenced by the presence of the macrocyclic ring, and vice versa. The ΔG° values for charge separation in 1−3 are close to 0 eV. Photochemical measurements have been made on 1−3, and they were all found to undergo photoinduced intramolecular electron transfer from the excited singlet state of the porphyrin macrocycle to the molybdenum moiety, yielding charge-separated states...

Synthesis and photochemistry of amido-linked, peripherally-molybdenated tetraphenylporphyrins

We explored the experiences of first year chemistry students of an Enquiry-Based Learning (EBL) approach to learning spectroscopy. An investigation of how students' perceived confidences changed as a result of their experience of using EBL in the spectroscopy course was carried out. Changes in the students' perceived confidence, both in their understanding of how spectroscopic techniques work and in their ability to interpret spectra were examined. In addition, an exploration of students' reactions towards the processes of EBL was carried out. This was achieved by various methods such as questionnaires, focus groups and an individual interview. Working with small numbers, a fairly positive picture has emerged, and much is consistent with the findings of others. Given that the aims of Higher Education need to encompass a wider range of skills (such as independent learning, group work, problem solving, communication skills), then this change in the way spectroscopy has been presented seems to offer much scope in embedding such employability skills.

Natalie M. Rowley

Papers

New Electrochromic Materials

Synthesis, Photochemistry, and Molecular Structures of Peripherally-Molybdenated Tetraphenylporphyrins and -metalloporphyrins

Synthesis, electrochemistry and spectroelectrochemistry of a porphyrin–viologen donor–acceptor diad

Synthesis and photochemistry of amido-linked, peripherally-molybdenated tetraphenylporphyrins

Enquiry-based learning: experiences of first year chemistry students learning spectroscopy