Abstract: Photocontrol of pH via Doped Conjugated Polymer Nanoparticles

Hello hello!

My name is Aaron Bayles, and I’m a junior at the College. Since the Fall semester of 2014, I have worked in Dr. Harbron’s chemistry lab, investigating a particular set of fluorescent polymer nanoparticles that can release acid into a solution upon irradiation by UV light, and track the amount of acid released by monitoring the change in the nanoparticles’ inherent fluorescence.

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Final Week-Best Results

Given some fears about my the properties of my particular azobenzene compound, we ordered a particular reagent to synthesize another azobenzene that will conserve all of the helpful properties of my current one, and allow it to recover faster. This should make my experiment much faster to run and overall more easily-applicable in the future.

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Initial Results with Photo-Acid Generator

I began retesting the remainder of my azobenzene sample to ensure that it has not decomposed over time. NMR and UV/Vis absorbance spectra confirmed that it was still good! With that settled, I could pick up where my project took a break in the Fall and hopefully overcome some of our hurdles,

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Back to Photo-Acid Generation!

As a result of the problems associated with working with my photo-base generator and the lack of options in choosing a new one (photo-base generating compounds are not very heavily studied), I decided to return to photo-acid generators, a type of compounds I worked with last Fall. The most promising was an azobenzene compound that released acid via a photo-isomerization process. It also matched very well with my nanoparticle polymer, PPE, to undergo FRET (Fluorescence Resonance Energy Transfer), the phenomenon that I am studying.

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Stubbornly Committed to PBG

So, I finally had my Photobase Generator, but lots of questions.

First, why did it seem to release acid upon irradiation? Upon reviewing the paper in which this molecule was synthesized, I discovered that they had published no actual pH data, only that the product had decomposed upon irradiation into two products, one of which was cyclohexylamine, the basic compound. Because cyclohexylamine was released, it had been classified as a photobase generating solution, which made sense. However, 6-nitrocoumarin was another product, and I couldn’t find any record of it’s acidic properties. My assumption was that perhaps the nitrocoumarin was actually more acidic than the cylclohexylamine was basic. Perhaps that would account for the drop of pH. However, quick tests proved that the nitrocoumarin was relatively basic, so that couldn’t be the solution.

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