Fifteen Eighty Four

It is rather appropriate that our book on conjugated polymers comes out 30 years to the month since I arrived in Cambridge to start working on them for the first time. When I joined Andy Holmes’s group in April 1994 polymer, OLEDs were a new and exciting field and were still some years away from commercialisation. Now OLED displays (some of which contain polymers) are ubiquitous and other conjugated polymer based organic electronic devices are on the cusp of commercial realisation. So a book covering the design, synthesis, and use of conjugated polymers is surely timely.

Like Andy, I had trained as a natural products chemist, and so found this new area rather different from my previous experience. One thing I started doing early on was mastering the literature on the subject, so I could better understand just what had been done and try to assess what might be promising new structures to make. Back then there was not much old literature, but new papers were coming out at a fast rate and searching regularly for new papers and patents and passing on what I found became one of my jobs within the group. As a result of my efforts to do this I was Andy’s first choice to help write a review article on electroluminescent polymers for Angewandte Chemie, which was the first comprehensive review on the subject. Being its author later helped me gain me jobs at Mainz and here in Singapore. A decade later I was again Andy’s first choice of coauthor when he was invited to write a review for Chemical Reviews on synthesis of electroluminescent polymers. That took a few years to complete, and it is a sign of how the field had expanded since our previous review that we went from around 300 references to over 2500 references, and we covered only the chemistry – there were at least as many physics papers on these polymers and their devices that we omitted. At the time I joked we had effectively written a book on the subject, and now Paul and I have written one.

One thing I had long felt was needed for any new person entering the field of polymers for organic electronics, was an accessible overview, which could tell them about the types of polymers that had been made, how to make them, and about what types of organic electronic devices they might be useful in. To help guide them in designing a new polymer, this would need to discuss structure property relationships, which are essential to developing the materials. It is not enough for a chemist to be able to draw a polymer structure and deduce a plausible synthesis of it, they also need to know if it is likely to have the necessary properties to be useful in a device, which is where they need to consult a physicist. Thus, a close working relationship between chemists and physicists becomes essential to advancing the field. A good example of this is the work done by a combined chemistry and physics collaborating team to identify the sources of the long wavelength emissions seen from polyfluorenes, which prevented them showing stable blue emission in devices. By determining the chemical species responsible for the unwanted emissions and how they were formed during synthesis and/or device operation, it was possible to design synthetic routes to avoid formation of these species and to rationally design molecules which showed more stable emission. I recall how my own first design of a stable blue emitting polyfluorene was successful but then I discovered from these people’s work it was not for the reason I had thought it was. It turned out my design didn’t just suppress aggregation, which had been thought to be the culprit, but prevented formation of the emissive defects that were the real culprits. Knowing the real cause of the unwanted emission did then enable me to design other polymers that gave stable emission. I am sure many other chemists and physicists have benefited from such insights obtained from the two disciplines working together and sharing their different perspectives.

Both my earlier reviews, while not neglecting the device and physics aspects, really concentrated on the chemistry aspects, i.e. on how to make the molecules, and though we did try to critically review the literature there was not much didactic elements in them, and of course they only covered LEDs (and lasers) as applications for the molecules, leaving out transistors, solar cells, and sensors. A review or book covering all classes of conjugated polymers and all applications which could be recommended to a new graduate student or postdoc to get them started in field, just didn’t exist as far as I knew.

As a result, when CUP approached me to write such a book I jumped at the chance. Of course, I couldn’t properly cover all aspects of the topic and so it was good to get Paul onboard to cover those aspects I was a bit lacking in experience or knowledge of, e.g. sensors, and to make sure both the chemistry and physics perspectives were covered. It took us quite while to write it (COVID was only one of the things that slowed us down) which had the converse advantage that it meant we could include the major advances in organic solar cell device efficiencies when state-of-the-art values jumped from around 10% to nearly 20%. Otherwise, I think we’d have had to start writing a second edition almost as soon as the first one was published. Now I think we have produced the sort of book I would have liked to have had access to when I started in the field. I hope we have struck a good balance between in explaining in detail some work which particularly illustrates some important point, and in particular which shows how one designs a new material with good performance, and a broad-brush overview of the field. And while the field of organic electronics continues to develop, e.g. in areas like flexible electronics, this seems at present to be mainly in device design with the active materials being the same ones used in older devices. So I hope our work will remain relevant for some time to come, and that readers find it useful and enjoyable to read.

Title: Conjugated Polymers for Organic Electronics

ISBN: 9781107008168

Author: Andrew Grimsdale and Paul Dastoor