Chemical Society Reviews Blog

In this Chem. Soc. Rev. review article, Kenji Kobayashi and Masamichi Yamanaka from Shizuoka University, Japan, give a detailed account of the host guest chemistry of a particular type of calixarene. Simple calixarenes are usually derived from, for example, a phenol and formaldehyde in an electrophilic aromatic substitution reaction. This yields a puckered basket structure containing a ring of methylene spaced phenols groups.

Calixarenes based on 1,3-dihydroxybenzene, also known as resorcinol (calix[4]resorcinarenes) are derived from similar chemistry and are described in this review. Capsule like materials containing covalently bound spacers between pairs of calix[4]resorcinarene units are briefly mentioned, while the majority of the review is devoted to capsules (or cavitands) containing substitutents capable of hydrogen bonding, metal coordination and other dynamic bonding, resulting in powerful, self-assembled host-guest interactions. The calix-[4]-resorcinarenes have extra rigidity in their structure, due to methylene bridging between the resorcinol oxygens of neighbouring units, with functional groups at the in-between 2-position.

Functionality introduced includes carboxylic acids, nitriles, halides, boronic acids, aldehdyes, alcohols and even a biypridyl unit. For example, a cavitand, containing phenol groups, not involved with other bonding, can be deprotonated to neatly bind pyrazine, in a hydrogen bound network, resulting in a dimeric self assembled cavitand.

Generic calix[4resorcinarene structures and a host-guest interaction with pyrazine]

Other examples are provided with mixed donors such as phenols and pyrdine groups in the same material. These heterodimeric cavitands can give access to a more advanced level of specificity, in these cases, for a variety of organic guests. Stronger bound capsule systems are described based on metal coordination. A nitrile substituted calix-[4]-resorcinarene and its palladium, platinum and counter-anion host-guest chemistry are briefly described, while examples self-assembled capsules with coordinating bipyridyl and dithiocarbamate units are also included.

The molecular and synthetic variety in this review is impressive. It is an enjoyable read, and should prove valuable to researchers in many disciplines. The application of such designed and potentially specific calix[4]resorcinarenes, and their mode of action in self-assembling and modifying guest reactivity is a  fascinating research area!

Read this Chem. Soc. Rev., Review Article today for free:

Self-assembled capsules based on tetrafunctionalized calix[4]resorcinarene cavitands
Kenji Kobayashi and Masamichi Yamanaka
DOI: 10.1039/C4CS00153B

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Organic polymers with metal-like properties have been an active area of chemical research for nearly seventy years. In this HOT Chem Soc Rev review, Adam Pron, Piotr Bujak, and colleagues from the Warsaw University of Technology and the Joseph Fourier University in Grenoble give an accessible and detailed account of the current state of the art in delocalised polymeric organic materials, focussing on neutral polymers which function as semiconductors. The application of semiconducting organic materials in devices such as FETs, LEDs, photovoltaic cells, photodiodes and magnetic photoswitches is described.

The synthesis, by Grignard reaction, transition metal or boron catalysed coupling reactions, and basic chemical characterisation of the major classes of organic semiconducting polymer are summarised.  This is followed by a detailed review of the chemistry and application of 4 classes of polymer in various electronic devices over the last three years.  The classes described are: polymeric semiconductors with n-type and with p-type conductivity, low-band gap semiconductors and also high-spin macromolecules.

Possible packing patterns in poly-3-hexylthiophene polymers

Methods of delivering highly ordered phases of polymers via solution processing are given, along with relevant electrochemical and magnetic information such as electron affinity, ionization potentials and magnetic moments. High-spin materials are of interest in spintronics, due to their potential for lower power consumption and faster information transfer than classical electronic components.

This is a very detailed review that successfully gives a comprehensive picture of the history, synthesis, characterisation, development and current state of the art of neutral semiconducting and high-spin polymers, and their application in modern electronics.

Read this HOT Chem Soc Rev article today!