Towards Insulated Molecular Wires to Order: The Active Template Approach to Conjugated Rotaxanes

Plastic electronics, electronic materials that are based on polymers, hold the promise of light weight, low power, cheap, versatile and mechanically flexible electronic devices, applications of which include flexible displays and wearable electronics based on circuits which can be printed using bubblejet printer technology. However, electrically conducting polymers (sometimes called molecular wires, MWs) are often unstable when operated the presence of air or moisture and can deteriorate due to interactions between the polymer chains. These drawbacks currently hinder the development of new commercial plastic electronic devices.

One approach which has been developed to help overcome these problems is to wrap the conjugated polymer in an insulating sheath, much as macroscopic wires are insulated using a rubber or plastic coating to prevent degradation and short circuits. These insulated molecular wires (IMWs) can be made by threading the conjugated polymer through the cavity of ring shaped molecules, to create a threaded structure, reminiscent of a bead on a thread, known as a poly-rotaxane (from rota, meaning wheel, and axel). This method has been shown to be extremely beneficial, dramatically improving the stability and properties of the conjugated polymer.

However, the existing methods for the synthesis of such poly-rotaxanes are currently extremely limited, hindering the development of these exciting materials. Our proposed research will greatly increase the availability of poly-rotaxane IMWs and will in the long term allow any polymer to be insulated with any macrocycle quickly and efficiently.

Ultimately, as a result of the proposed work we will be able to create designer insulated molecular wires to order, potentially revolutionising the use of these novel materials for plastic electronic devices.

We propose to develop new methods for the synthesis of organic semiconductors that are insulated at the molecular level. These materials have been shown to have significantly enhanced properties, compared to their non-insulated equivalents, and the proposed work has the potential to generate a number of types of impact.

1) Academic Impact

The proposed research will have wide academic impact in areas which are typically considered fundamental and applied. At the fundamental level, by providing new methods for the synthesis of complex mechanically interlocked molecules we are developing tools for application not only in the synthesis of insulated molecular wires but also in the realisation of other novel mechanically interlocked materials with application as sensors, prodrugs and molecular machines. At the applied level, our proposed research will lead to increased availability and a deeper understanding of IMWs as materials for applications in display devices, photovoltaic devices and plastic electronics in general.

For more details see the "academic beneficiaries" section.

2) Technological/Commercial Impact

Rotaxane insulated molecular wires have been demonstrated to behave as semiconductors with enhanced photo- and electro-luminescence efficiencies and increased environmental stability as compared to their non-insulated counterparts. These properties make them ideal materials for application in robust plastic electronic devices suggesting they have potential to make a significant technological impact as components in commercial devices such as flexible displays, lighting systems, solar cells and sensors for biological molecules. Rotaxane insulated molecular wires also display improved stimulated emission compared with their non-insulated analogues amplified suggesting they may find application in cost effective, polymer-based continuous wave solid state lasers. These devices are key components of next generation fibre optic devices.

3) Societal Impact

The immediate societal impact of the proposed research will be the training by SMG of a highly skilled researcher (the PDRA) capable of carrying out research at the interface of organic, synthetic supramolecular, materials and plastic electronics. At the end of the project they will be capable of generating new ideas across a broad range of scientific areas and carrying out innovative research in academic or industrial environments. They will also have gained collaborative skills through interaction with researchers in other groups and other areas in order to design, test and evaluate new materials. This individual will be well positioned with the unique skill set gained during the project to make a significant contribution both within the UK and internationally.

In the longer term, the proposed research will accelerate the application of IMWs in real world plastic electronic devices with enhanced properties such as brighter low-energy lighting systems, flexible displays and wearable electronics. This has the potential to enhance UK living standards directly both through the creation of whole new types of devices and through lowering the cost, improving the performance and increasing the energy efficiency of existing products. The UK is also well positioned to take advantage of progress in the field of plastic electronics in terms of job and growth creation given the position of the UK as an acknowledged leader in the field both academically and industrially. Given the relatively low cost of plastic electronic manufacturing facilities (compared to silicon semiconductor technology) this includes the potential to assist in increasing the relative size of the manufacturing sector in the UK.

Finally, the production of cheap and flexible photovoltaic devices, along with the low power consumption of plastic electronic devices, both in the manufacturing phase and in use, means that replacing silicon based-devices, will contribute to combat climate change.