Liquid crystals, as commonly used in displays, behave between a liquid and a solid, with their molecules being oriented and partially ordered as in a crystal, but are less rigid and more mobile, like a liquid. However, when a current is applied to them, the liquid crystals can switch between different states. Metal clusters, on the other hand, are aggregates of a few metal atoms that are held together by metal bonds and show unusual electronic, magnetic and optical properties due to properties that arise from the metal-metal bonds in the cluster.
The study, published in the journal Angewandte Chemie [Molard et al., Angewandte Chemie (2010) doi: 10.1002/anie.201000325], united the characteristics of both types of material in the form of a new class of materials called clustomesogens, which contain metal clusters in a liquid-crystalline phase.
The wide array of specialisms in the research team, with backgrounds in the solid state synthesis of metallic clusters, nanomaterials, nanoparticles and supramolecular chemistry, all contributed to their development of these nanostructured, cluster-based materials. The clustomesogens take advantage of the cluster’s peculiar properties – high luminescence in the red/infra-red (NIR) area – and the supramolecular chemistry concept of self-assembling.
Liquid crystals that contain bonds between metal atoms are rare and usually limited to compounds in which just two metal atoms are connected in each unit. The study obtained liquid crystals that contain octahedral clusters made of six molybdenum atoms, a technically challenging feat, especially as the coordination behaviour of one nanometer-sized cluster is poorly compatible with the structural requirements of the liquid-crystal phases.
As the compounds are liquid crystal on a wide range of temperatures between nearly 20°C and 100°C, this makes them suitable for the fabrication of working devices, such as in analytical instrumentation and potentially in flexible display technologies. These types of cluster are also often described as a molecular light bulb because of their outstanding photoluminescence properties in the red/near infrared range when excited over a broad range of wavelengths. This type of material may also therefore be useful for the production of red displays and infrared signals.
The team now hope to continue their research by reaching a better understanding of molecular structures and nanostructuration relationships, in order to achieve control over the organisation process and for building devices that illustrate the high potential of such compounds.