Towards the Computational Design of Highly Emissive Organic-Single Crystals

Summary

Light emitting materials find applications in display technologies, optical communication, data storage, biological sensing and solid-state lasing. Organic conjugate molecular systems represent versatile blocks for the development of cheap and flexible functional materials. In particular, their single crystals (OSCs) can exhibit favourable properties with respect to their amorphous counterparts such as better thermal and photochemical stabilities, large refractive indexes, highly polarised emission, and enhanced charge-carrier mobility. However, their emissive properties are severely affected by nonradiative mechanisms facilitating a fast conversion to the ground state. These mechanisms include aggregation-induced quenching, intersystem crossing and internal conversion. New strategies for the design of highly emissive OSCs should provide routes to minimise deactivation through these pathways.

The development of fluorophores with an enhanced emissive response in the solid state has become a very active area of research. Fluorophores displaying excited state intramolecular proton transfer have shown promising properties as solid-state lasers (ESIPT-OCSs). But in order to achieve a rational design of these materials, a fundamental understanding of the underlying phenomena at the molecular and crystal levels is required. Computational modelling can aid materials design proposing candidate structures with tailored properties.

Predictive models for emissive materials should include the effect of nonadiabatic and excitonic effects. Despite their potential applications, there is a lack of general computational tools to study phenomena at the interface between molecular photochemistry and material sciences. The primary goal of this research programme is to develop computational chemistry strategies towards the design of efficient emissive OCSs. We will achieve this by developing a systematic investigation of nonradiative mechanisms in model ESIPT-OCSs materials and producing new software for the exploration of excited states and nonadiabatic phenomena in the crystal environment considering electrostatic embedding techniques. The codes will be made freely available to the community through open access repositories.

Mechanisms for aggregation induced phenomena in the solid-state will be investigated with a focus on establishing structural features enhancing the emissive response. The role of intramolecular (substituents, geometry) and intermolecular (weak interactions and crystal packing) factors affecting the nonradiative deactivation pathways will be considered. Based on this new knowledge and assisted by the computational tools, candidates for highly emissive materials will be proposed and tested by our experimental collaborators, providing feedback to examine our predictions. In the longer term, all these strategies will open up new possibilities in the design of OCSs materials with tailored properties.

Impact Summary

The proposed research develops strategies for the computational design of organic materials with a high emissive response. We will create fundamental knowledge of the phenomena associated with their light response. This research will benefit scientists working in several areas such as computational chemistry, organic chemistry, functional and photonic materials.

Economic Impact

While this programme will create fundamental understanding, computational design of materials with tailored properties can have a major impact on technological applications such as display technologies, optical communication, data storage, biological sensing and solid-state lasing. Our collaborations with two experimental groups will allow testing our computational principles and engaging with industry. A broad strategy of publishing and dissemination will be implemented to enhance the visibility of our research.

It has been recognised by the EPSRC that computational modelling plays an increasingly important role in the development of the Physical sciences. The UK's prosperity depends on not only applying computational techniques but also on the development of new computational methods. Through this research program, we will implement software to investigate complex phenomena in the crystal environment with applications in the computational design of organic materials from first principles. These codes will be freely distributed among the scientific community which will maximise their usability and impact.

Societal Impact

Research and training in the area of computational chemistry can impact in several areas of Physical sciences and Engineering. The immediate social impact of the proposed research is the training of a highly skilled researcher (PRDA), who will benefit from the rich multidisciplinary environment at QMUL and all the available facilities. The PDRA will acquire a unique set of skills that will improve their employability. Programming skills and expertise in the high-performance computing are greatly valued in the work market within and beyond academic professions. The PDRA will also contribute to the supervision of postgraduate and undergraduate students working in the research group. Thus, the PhD and master students will also receive training and contribute to the knowledge creation. The PI, who is an early career researcher, will also take advantages of the leadership opportunities generated from the proposed grant.

We will engage with the general public promoting public discussions on the role of modelling in technology and daily life through forums and seminars facilitated by the Centre for Public Engagement at QMUL. Videos and simplified models will be used to explain the principles underlying material discovery in plain language. Social media platforms will be exploited to broadcast our findings and reach the general public.