Strategic Design of Conjugated Polymer Materials for Sensors and Solid-State Lighting

Strategic Design of Conjugated Polymer Materials for Sensors and Solid-State Lighting Niamh Willis Fox A thesis submitted to the University of Dublin, Trinity College for the degree of Doctor of Philosophy. Under the supervision of Dr. Rachel C. Evans School of Chemistry November 2015 Trinity College Dublin Declaration I declare that this thesis has not been submitted as an exercise for a degree at this or any other university and it is entirely my own work, except where otherwise cited, referenced, acknowledged or accredited. I agree to deposit this thesis in the University’s open access institutional repository or allow the library to do so on my behalf, subject to Irish Copyright Legislation and Trinity College Library conditions of use and acknowledgement. …………………………………………… Niamh Willis Fox B.A. Mod. i Light (…) gives colour and brilliance to all works of nature and of art, it multiplies the universe by painting it in the eyes of all that breathe. -Abbé Nollet The trouble with an open mind, of course, is that people will insist on coming along and trying to put things in it. -Terry Pratchett ii Acknowledgements I would almost say writing these acknowledgements was the hardest part of writing this thesis (almost but not quite!!), what if I forgot or offended someone!? However, I have to say, it was the easiest thing in the world to realise that first and foremost I want to thank my supervisor Dr. Rachel Evans. As a shy young undergrad I never could have imagined that I would have ended up with a supervisor so supportive of my love of the musical talents of Taylor Swift or one who would subtly instigate a group uniform by buying the same clothes as everyone else. But in all seriousness, I could also never have dreamed I would be lucky enough to have a supervisor as generous with her guidance and support. I have had an amazing four years both personally and professionally and I couldn’t have done any of it without you, so truly thank you Rachel. I was privileged to spend a small portion of my PhD in Boston. They say never meet your heroes but Tim you proved that wrong. Thank you so much for taking me as essentially a blow in from the street and for treating me with the same care and concern you would one of your own students. Also to all the ‘Swagerites’ that welcomed me with open arms from the very start and made my stay unforgettable; Chris, Myles, Sibo, Yoshi, Greg, Maggie, Joe, Vera and Laura. I couldn’t have done this work left to my own devices; I got endless help from the technical and academic staff. I want to thank John and Manuel for their measurements in the NMR services and particularly to Manuel for help with essentially all of the instruments I set my hands on and for answering my emails even if he was in the pub. Patsy, Helen and Tess thank you for always making me smile, genuinely what would we have done without you. As they saying goes ‘there’s only one Patsy Green’ don’t worry girls, Jude and I will teach you the song on our holiday. To all the members of the Evans group past and present who not only made it a pleasure to come into college everyday but who also put up with all my ridiculous demands like full on costumes for the Keeley cup and other such messing. Special shout out to my lunch buddy Barry, I don’t think I’ve had to clean my tea mug at all in the last two years. It will come as no surprise to anyone that there are two people that I have to single out, Adam and Jude (don’t worry Jude he’s just going first because he is older). You guys have been right beside me for every moment of this PhD, from the ridiculous (going to pick our stuff up from the Law/Lost Society) to the sublime (suited and booted for the Scholars ball). If I get nothing else from this experience I will have gained two of the best friends the world has to offer, who would totally invite me to their wedding. I also managed to pick up some other friends along the way. Dee, Ian and Moylan (who immediately took me under her wing), these last few years would have been a much less sociable and entertaining experience without you. I also have to mention my hockey team who attempted (and failed) to get me out running and who almost made 9 am matches on Saturday mornings bearable. Graham and Christian, thanks for all the holidays and staying up until crazy times watching addictive TV shows. Fergus, I have no idea how we managed to get this far without freaking each other out, but to me you will always be more than a ‘one act cat’. I also have to mention Emily who had no choice in our friendship in undergrad, I just didn’t leave her house. I’m delighted every day to realise the Stockholm syndrome hasn’t worn off and she now even voluntarily makes it to my house to supply a cup of tea and some dry humour. And to my touchstone, Classic Beth, I feel like I don’t have to tell you all my deepest thoughts (most of them aren’t that deep anyway), you seem to know what they are before I have them. I am never immune to your charm, no one has or can make me laugh and smile so much. It has been wonderful to be part of this friendship that we have been (Met)formin. Last but not least my family, aunts and godparents, thank you for all the love and happy days. Most specially to J, Sheila and Orla (who I never realise how much I miss until she is gone on another amazing adventure). I’m sorry you guys had to put up with the brunt of the bad moods and didn’t always get to see the good. Thank you for relentlessly picking me up, dusting me off and setting me in the right direction again. There are no words for how much love and admiration I have for you guys. iii Abstract Conjugated polymers (CPs) have shown extreme promise in a range of applications such as optical sensors and light-emitting devices due to their exceptional optoelectronic properties, low cost and solution processability. CPs are particularly sought after as sensory materials due to their property of amplified quenching, which can facilitate analyte detection at nanomolar concentrations. This work begins by examining the use of a polyfluorene (blue-emitting)- polythiophene (red-emitting) diblock CP with complementary optoelectronic properties attributed to both blocks, which enables fluorimetric and colorimetric detection of biologically important nucleotides. The magnitude of the optical response is sensitive to both nucleotide geometry and charge. The proposed mechanism behind this process involves electron transfer from the nucleobase to the polythiophene block, mediated by the CP triplet state. Although the vast majority of CP-based sensing schemes involve the detection of electron- poor analytes by electron-rich polymers, there are relatively few examples describing the contrary scenario, electron-rich analyte detection by electron-poor polymers. In Chapter 4, the possibility of increasing the discriminatory action of such electron-poor CP sensor systems through the creation of polyrotaxane species is investigated, whereby macrocycles of differing sizes are exploited to control the effective volume in which the CP and analytes interact. This system may be deposited into the solid-state, whilst retaining its sensing properties to gas phase analytes. The lifetime of any solid-state CP-based device is limited by the photo- and thermal instability of the CP. Incorporation of CPs into an inorganic host allows modulation of the optical properties and aggregation state of the CP, whilst simultaneously improving the environmental stability. However, due to the chemical incompatibility of the two components, inhibiting phase separation across all length scales can be challenging. In Chapters 5-7, the potential of di-ureasil hybrids, comprised of an organic polyether grafted onto a siliceous network via urea linkages, as host materials for CPs is investigated. Firstly, blue-emitting polyfluorene-phenylene CPs were physically immobilised into the di-ureasil to form a Class I hybrid. Examination of the optical properties indicated that both the CPs and the di-ureasil host contribute to the photoluminescence properties giving rise to a dramatic enhancement of the photoluminescence quantum yield (PLQY) to ~60%. This is due to effective prevention of CP aggregation by the di-ureasil host and efficient energy transfer between the two components. Subsequent inclusion of the red-emitting CPs, MEH- PPV and P3TMAHT, was carried out in an effort to extend the emission colour from the inherent blue emission of the di-ureasil host across the visible spectrum. The emission colour of these samples was found to be tunable across the blue-white-yellow spectral region due to incomplete Förster resonance energy transfer from the di-ureasil to the CP. Finally, as the properties of such organic-inorganic hybrid materials depend on the interface between the two phases, a polyfluorene was covalently-grafted directly to the siliceous network of a di-ureasil. Energy transfer between the di-ureasil and the CP was observed leading to an improved PLQY when compared to a thin film of the pure CP. On comparison with the physically immobilized samples previously discussed, the magnitude of energy transfer was found to be reduced for the grafted species.

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