Asymmetric Synthesis and Study of Platinum Metallahelicenes in Circularly Polarised Phosphorescent Organic Light Emitting Diodes (CP-PHOLEDs)

Organic light emitting diodes (OLEDs) require an emissive electroluminescent layer of an organic semiconductor material located between two electrodes, where at least one of the electrodes is transparent. Such devices are revolutionising display technologies due to thin dimensions, faster switching and higher contrast ratios. Indeed, currently the market for such devices is valued at >$2.5B. Devices that emit circularly polarised electroluminescence (CPEL) should have vast translational potential in photonic technology, such as improved LCD backlighting, colour-image detection and stereoscopic displays, optical communication, and quantum computing, however to date the problem of directly generating CPEL has not been solved. Successful development of this technology is reliant on the production of light-emitting devices of controllable circular polarisation, tuneable emission wavelength, and high colour purity. While wide-band reflective polarisers may be used as passive components in OLED devices to achieve CPEL, the direct generation of CPEL would be far more elegant, and favourable in terms of energy efficiency and production cost. This research will develop efficient methods to synthesise intrinsically chiral phosphorescent molecules and use these to fabricate CP electroluminescent devices, in an attempt to demonstrate highly efficient CPEL.

The successful direct generation of circularly polarised electroluminescence (CPEL) would have a transformative effect on a range of disciplines including physics and materials science. Such work would have significant impact on current knowledge, which could be exploited in a number of translational areas. The UK is a pioneer of OLED technology and needs new innovation to maintain this position. Indeed, former chief scientific advisor Sir David King has recognised this potential highlighting "in Britain we have a world-leading position in a technology that could wipe out the silicon chip" "I am talking about plastic electronics". Taking alternative LCD backlighting as one example of the exploitation of this work, current technologies rely on polarising filters that effectively cut out 75% of the light used in these displays. Combined with absorption by the colour filters and at device interfaces, only 4% of the light used is transmitted. The use of a polarised light source, coupled with tuneable colour components would remove this need, thus leading to significantly more energy efficient displays. Such displays with a lowered carbon footprint would be of clear environmental impact.

The development of a novel class of intrinsically chiral phosphorescent semiconductors would have international impact in a range of fields, and is likely to promote new research directions. While the chirality of helicenes has been known since the 1950s, only sparse reports have emerged on their use in plastic electronic devices; the metallahelicenes are currently totally unstudied in this regard. The preparation of highly efficient CP emitting devices is also an unsolved problem. This project will tackle these shortcomings using innovative chemistry and materials science.

As outlined in the 'Academic Beneficiaries' section, the science proposed herein would have significant impact on current academic and industrial knowledge in a diverse range of disciplines including chemistry, physics and materials science. It will therefore impact the knowledge economy in such diverse areas. The translational aspect of this proposal - fabricating CP-PHOLEDs - would be of high interest to a number of key industrial companies (Cambridge Display Technologies, Plastic Logic, Merck, BASF, etc) involved in plastic electronics research. Indeed, the approach taken will allow solution processing of the luminescent layer of the resultant CP-PHOLEDs. Panasonic are developing an ink jet printed polymer AMOLED display using PFO polymers, and DuPont Displays are developing solution-processed AMOLED displays using slot-coating and nozzle-printing. Our approach should therefore readily translate to exiting production approaches. Technological advances resulting from this work would have clear ramifications in terms of wealth creation within the UK; the current OLED market is valued at >$2.5B. One key use of CP-PHOLEDs would be as high efficient LCD backlights (see Grell, M.; et al. Adv. Mater. 2001, 13, 577 for example). If this was taken as an example for the exploitation of this work, a novel polarised light source, coupled with tuneable colour components would lead to significantly more energy efficient displays. Such displays with a lowered carbon footprint would be of clear environmental impact, and therefore of benefit to society as a whole. LG have, for example, employed OLED backlights for LCD displays and therefore would likely be interested in our novel technology, once developed. In general terms, CP light emitting devices would have a strong impact in current and future technologies such as tomography and integrated optical quantum computing. Finally, further training of skilled-coworkers and the educational experiences of students involved in this science would also have clear economic and societal impact.