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Multicoloured ambipolar conducting polymers for single polymer optoelectronic devices

Final Report Summary - AMBIPOD (Multicoloured ambipolar conducting polymers for single polymer optoelectronic devices)

AmbiPOD - a joint international research and staff training programme concentrated on developing new organic materials for electroabsorptive and electroemissive applications, pursued five key objectives:

› Design, develop and synthesise novel conductive organic donor – acceptor materials,
› Characterise these materials to screen them for potential applicability in passive or active optoelectronic devices,
› Fabricate test devices and assess their performance qualities,
› Provide multidisciplinary researcher development opportunities,
› Strengthen multilateral scientific cooperation between European Research Area and key worldwide academic stakeholders,

The centrepiece of research efforts was to develop new ambipolar molecules holding promise of effective application in multi-coloured electrochromic and electro-emissive devices. Capitalising on the project parties’ backgrounds, a number of new different donor and acceptor π-conjugated units have been brought to stage and structures involving different combinations thereof have been proposed. The building blocks encompassed a broad range of heterocyclic structures known to demonstrate a diverse range of electron releasing or withdrawing traits. New donor and acceptor structures have been proposed combining computationally predicted high electron affinity π-conjugated frameworks and aggregation hindering functionalities toward formulating new materials. Combining these units together in different arrangements and sequences, new ambipolar compounds have been proposed and their spectral properties evaluated using state of the art quantum computation tools developed for pi-conjugated systems with substantial charge transfer contribution. Investigation and formulation of reliable and robust design rules for controlling the conformation and therefore properties of donor - acceptor polymers as a function of these non-covalent interactions was made. Synthesised donor – acceptor targets demonstrated diverse redox activity complemented by intriguing electroabsorptive and electroemissive properties, bringing together several of the themes identified during AmbiPOD activities: planarising (or disruptive) non-covalent interactions, intelligent material design and synthesis, and a repetitive donor-acceptor backbone to provide ideal material properties. Compounds demonstrating good propensity towards electro-polymerisation and yielding electrochromic films when electropolymerised from their monomer solutions have been developed. Rich electrochromic performance of resulting polymer films across the visible light spectrum gave promise of developing new electrochromic devices. Flexible rapid-switching electrochromic windows were fabricated and their characteristics tested on reference polymeric electrochromes. Developed methodology will enable to screen other π-conjugated polymers for efficient colour-switching performance in device operating conditions. Efficient potential driven light emission spanning full colour gamut was obtained from thermally evaporated thin films of investigated ambipolar compounds. Observing careful and conscious selection rules of tailoring charge transport layers for maximising radiant output, efficient blue, green, orange and deep red electroemissive demonstrator devices have been fabricated and their performance evaluated. Emission mechanisms responsible for the high light output of fabricated devices were scrutinised and effective electron – hole recombination phenomena like TADF (thermally-activated delayed fluorescence) and exciplex electroluminescence have been identified as principal contributors. Selected compounds featured broadband light emission across visible spectrum, translating to highly sought-for organic white light emitting materials. Structure – property relationships inferred from these studies will help further the knowledge of electron – light interactions aiding design of new electrochromic and electroluminescent polymeric materials.
The project, as a multi-disciplinary research programme conducted across Europe and abroad, focuses on practical training of the next generation of experts, furnishing them with necessary skills to face research and technological challenges in the field of organic electronics. The research needed to provide this training facilitated vertical integration of different knowledge areas in parallel with horizontal application of technologies and skills across different fields of electronic applications. The career development plan consolidated the training objectives, providing an outstanding opportunity for all researchers to foster their knowledge and skills and benefit from excellent career prospects that will profit the whole community. Accomplished training and research objectives deliver important impact and benefits for Europe’s Nanoscience & Nanotechnology sector and for its citizens.