Redox Switchable Photonic Materials Based on Organoimido-Polyoxometalate/Cyclodextrin Host-Guest Complexes

Lead Research Organisation: University of East Anglia
Department Name: Chemistry

Abstract

Photonic materials interact with light in useful and interesting ways. They enable its manipulation, and conversion into other forms of energy. One important class of photonic materials are non-linear optical (NLO) materials, which can be used to manipulate and adjust the properties of laser light beams. For example, they are used to make green lasers by second harmonic generation (SHG) from an infra-red source, and in electro-optic (EO) modulators that transfer digital electronic signals into fibre-optic telecommunications.

At present, most commercial NLO materials are simple inorganic salts. These are inexpensive, durable and ideal for simple SHG applications. However, in telecommunications and computing they suffer from slow speed, as their responses originate from displacement of (relatively heavy) ions in response to the electric field of light. Molecular organic and metal-organic materials promise faster responses, because they arise from displacement of lighter, faster electrons, and also rational property tuning and the possibility of rapid property switching (i.e. on/off for optical or electrooptical transistors). But it is difficult to obtain molecules combining high NLO activity with adequate transparency and photostability, and adding the ability to reversibly switch between on/off states is a still greater challenge. Recently, we discovered a promising new class of molecular NLO materials based on polyoxometalates (POMs) - a type of molecular metal oxide cluster - connected to organic groups. These POM-based chromophores (POMophores) obtain high NLO coefficients from materials with small, stable organic groups and excellent transparency, and show redox properties that could be used to switch the NLO response.

The next stage, addressed in this project, is to assemble POMophores into bulk materials that can be used in devices - specifically EO modulators and transistors. To do this, we must find a way to align all of the POMophores so that they point in the same direction and give a net NLO effect. This is challenging, as methods for controlled assembly of POM-based materials are currently very limited, and to achieve the goal we will develop a new approach where we first trap the POMophore in a molecular container. The molecular containers are designed in such a way that they form a film where the desired molecular orientation is forced on the POMophore. In addition to organising the POMophores to give bulk NLO properties, the containers will also protect them from degradation when we investigate redox-switching of the NLO response.

POMs offer many other properties beyond non-linear optics - for example many POM clusters are excellent catalysts or photocatalysts due to their ability to rapidly accept and transfer electrons, some have magnetic and/or luminescence properties introduced by incorporating suitable heterometals into the POM framework, and POMs have also demonstrated anti-viral activity. Therefore, we expect that other areas of chemistry and materials science will benefit from methods enabling their encapsulation and control over their positioning on the nanoscale. Possibilities could include selective catalysis, solar energy conversion, memory devices, and even targeting of biologically/medicinally active POM species for therapeutic interventions. This project will lay the groundwork necessary for such developments, as well as potentially producing the new, high performance bulk NLO materials needed for future telecommunications and computing.

Planned Impact

I anticipate impact in three main areas:

1. Economic and Social Impact: This project is in the general area of photonic materials. The UK photonics industry is one of the success stories of our economy post-2008: it is in the global top 5, now worth >£12.9 bn, is growing at 5.3% p.a., and employs 65,000 people who have 3x the UK average productivity per worker. Continuing this trajectory requires development of new and innovative materials, as we will do in this proposal focused on new non-linear optical materials. The goal is to produce a basis for high performance electroptic (EO) modulators, used to convert digital electronic signals into optical signals, and eventually, electroptic transistors that could be a basis for optical data processing.
These could facilitate a move from electronic to electro-optical and all optical data transmission and processing, increasing the speed, and lowering the power consumption of ICT. As our demand for computing power and telecommunications speed is seemingly insatiable, and ca. 10% of global electricity consumption is now attributed to ICT, the potential economic benefit of improved technology is clear. The materials we study are also potentially relevant to optical power limiters and imaging agents, another source of economic impact. The project also supports the UK economy by training highly skilled workers - the PDRA will gain skills in synthesis and measurement that are widely marketable in academia and beyond. Moreover, forming individuals with high level problem solving and other transferable skills benefits society in numerous ways, beyond specific scientific knowledge.

2. Environmental Impact: Significant, positive environmental impact will emerge from this project if it can contribute to development of materials for optical telecommunications and computing. This is because the current rate of increase of ICT use is not sustainable without technological change: while the power consumption of our devices (computers, phones, smart TVs) may seem small compared to household heating, lighting and transport, the power consumption of networks and data centres is massive. The global energy footprint of ICT comfortably exceeds that of aviation, and it has been suggested that watching one hour of streamed video consumes more electricity in remote networks than two refrigerators do in a year. As optical telecommunications and computing promise inherently higher bandwidth and lower energy consumption, they can facilitate a continued and sustainable ICT revolution.

3. Social and Cultural Impact - through fundamental science: This project involves development of new methods, new materials and measurement of their properties, so it clearly impacts on fundamental science. The POM nanostructure assembly methods I propose will be completely new, and thus could influence science for some time - they (encapsulation by a molecular container), and their proposed application, are also attractive to lay audiences of all ages and potentially an excellent vehicle for outreach.

Publications

10 25 50
 
Description The host guest chemistry is working more or less as planned however I do not wish to say more until it is published. Fully understanding this key, underpinning aspect has taken more time than expected and I am continuing to work on data interpretation even though the grant is now finished.

The development of more stable, redox switched materials worked very well. We have increased optical non-linearities by up to 50% on our previously published materials, have one excellent candidate for switching and several others that show interesting behaviour in this regard. We are exploring whether we have IP worth protecting while we work up a publication to be submitted this year. However, truly valuable IP in this domain would be a fully developed material and we are still some distance from that (see below).

With regard to materials, translation onto surfaces has proved to be a challenge - it is hard to obtain sufficient loading and unexpectedly, crystalline materials are forming instead of the desired oriented mono-layers. This part of the project would need a complete re-design to deliver the project objectives. I need to think about this and look for fresh funding.
Exploitation Route I do not wish to elaborate at this stage. We need to decide if IP protection is relevant and publish
Sectors Digital/Communication/Information Technologies (including Software),Energy,Other

 
Description Leverhulme Trust Research Project Grant: Redox-Switchable Polyoxotungstate Charge Transfer Chromophores
Amount £193,677 (GBP)
Funding ID RPG-2020-365 
Organisation The Leverhulme Trust 
Sector Charity/Non Profit
Country United Kingdom
Start 04/2021 
End 05/2024
 
Title New cell design for electrochemically-switched NLO measurements 
Description We built a new electrochemical cell with optical glass on three sides and a small volume to facilitate electrochemically switched hyper-Rayleigh scattering measurements 
Type Of Material Improvements to research infrastructure 
Year Produced 2021 
Provided To Others? No  
Impact Design will be made available when research is published 
 
Description Collaboration with Prof Koen Clays (KU Leuven) on NLO measurement and redox switched NLO 
Organisation University of Leuven
Country Belgium 
Sector Academic/University 
PI Contribution We provided materials, a pair of hands for measurements (done by PhD student Bethany Hood on secondment), and expertise in electrochemistry
Collaborator Contribution They provided knowledge and facilities for hyper-Rayleigh scattering (measurement of second harmonic scattered light).
Impact Several outputs - research papers - associated with 2014-16 EPSRC award. Disciplines - inorganic chemistry, molecular photonics, photophysical measurement. These are: https://doi.org/10.1039/C6DT00115G https://doi.org/10.1021/acs.inorgchem.7b00708 https://doi.org/10.1039/C8DT01491D
Start Year 2014
 
Description Small Angle X-ray Scattering with Materials Science, Cambridge 
Organisation University of Cambridge
Department Department of Materials Science & Metallurgy
Country United Kingdom 
Sector Academic/University 
PI Contribution Materials, pair of hands
Collaborator Contribution Help with interpretation We pay for instrument access
Impact We have data that will support an application for synchrotron time.
Start Year 2019
 
Description Attendance at IRN Polyoxometalate meeting in Paris, July 2019 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Meeting of international polyoxometalate chemists to discuss set up of new network aimed at stimulating research and interface with business, media, public etc.
Year(s) Of Engagement Activity 2019
URL http://www.irn-pom.uvsq.fr/about
 
Description Invited talk at RWTH Aachen, Germany 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact Talk given to faculty ("professional practioners"), post-doctoral researchers and postgraduate students at RWTH Aachen University
Year(s) Of Engagement Activity 2018
 
Description Invited talk at the University of Sussex 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Postgraduate students
Results and Impact Visited University of Sussex and gave a talk containing research from this award.
The audience were a mix of postgraduates, post-docs and academic staff. I received some engaged questions afterwards.
The main outcome is potential future collaboration and use of Sussex mass spectroscopy facility by me and other UEA faculty.
Year(s) Of Engagement Activity 2018
 
Description Poster Presentation at the RSC Southern Dalton Meeting, Oxford 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Postgraduate students
Results and Impact Poster presentation by PDRA Kevin Vincent, and PhD student Bethany Hood made at the RSC Southern Dalton meeting in Oxford, September 2019.
The main impact was communicating our work to peers plus other groups (sponsors, publishers) present at the meeting and gaining new ideas from interaction iwth them.
Year(s) Of Engagement Activity 2019
 
Description Poster at RSC Dalton Joint Interest Group Meeting 2021 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact Poster presentation by my post-doc Kevin Vincent describing our findings on interactions between polyoxometalate anions and cyclodextrins (Objective 2 and 4 of grant)
Year(s) Of Engagement Activity 2021
URL https://www.rsc.org/events/detail/46627/dalton-2021-joint-interest-group-meeting-and-dyme
 
Description Talk at the RSC Dalton Joint Interest Group Meeting 2021 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact Talk given by my PhD student Bethany Hood on synthesis and properties of new polyoxometalate based NLO chromophores, synthesised as part of objective 1 of the grant.
Year(s) Of Engagement Activity 2021
URL https://www.rsc.org/events/detail/46627/dalton-2021-joint-interest-group-meeting-and-dyme