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,

One of the main problems with using UV-light in any experiment is the nearly inevitable unpredictable consequences. And it makes sense: blasting a sample with high-intensity light has the potential to affect every bond in a molecule, so it’s best used with care. In photochemistry, the result of irradiating a sample for too long or with too high intensity is a phenomenon called photobleaching. It can take a variety of forms, and isn’t always undesirable, but for our purposes, it damages my nanoparticles beyond repair and makes them unusable in their intended application.

Being mindful of potential photobleaching, I performed all of my irradiation trials with low-intensity light. All of my experiments clearly showed acid release, but the desired reversibility was generally very difficult to achieve. The UV/Vis spectrum showed reversibility, but pH did not corroborate. In fact, pH seemed to continuously decrease even after the light turned off. As previously stated, the azobenzene can take either a cis or a trans form, and those can each be either protonated or unprotonated. The relative abundances of each are unique to the acidity of solution and the solvent, and their interactions are still unknown, so the conflicting UV/Vis and pH readings isn’t very surprising, just annoying.

Further research showed that my compound recovers very slowly in our chosen test solvent (1:1 acetonitrile and water) after irradiation, almost prohibitively slowly. This could also lead to some discrepancies in our data. I will do further investigations into different solvents to find what works best for testing, even though the final product will be in water.