Spectroscopic investigations of dendritic polymers as molecular containers

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Previous research has shown the fluorescent probe phenol blue will associate with the dendritic polymers polypropyleneimine (PPI) and polyamidoamine (PAMAM). The phenol blue will associate with the core of the dendrimer molecules. This association revealed previously unknown information about the microenvironment of the dendrimer interior, including accessibility, size, and polarity. The association was also found to be very stable over time. When additional solvent was added to the solution to try and pull the dye molecule out of the dendrimer, the dye remained entrapped in the dendrimer interior. The current research investigated the strength of the phenol blue-dendrimer association to determine if the dye molecule would remain entrapped through the process of solvent replacement with methanol, a solvent in which phenol blue is very soluble. Using UV-vis absorption and fluorescence techniques, it was found that the phenol blue is retained by the dendrimers. Even though the associated complex is in methanol only, the interaction with the solvent is not enough to pull the phenol blue out of the dendrimer and the dye remains entrapped. Once it was determined that the dye was retained by the dendrimer, further research examined the accessibility of the entrapped dye. The samples were flushed with nitrogen to remove any dissolved oxygen in the solution, as oxygen is known to quench fluorescence signals. There was a change in the fluorescence intensity in both water and methanol, indicating that the nitrogen was able to interact with the dye and remove oxygen from the system. Triethylamine was also added to the samples to determine if a larger molecule could travel to the core and interact with the entrapped phenol blue molecules. The results showed changes in the fluorescence intensity in response to the addition of the triethylamine to the system. Although the results were inconsistent, they show that the dye is accessible to larger molecules in both water and methanol. This research shows that the entrapped phenol blue remains in the dendrimer core through solvent replacement. The dye molecule also remains accessible to other molecules, such as oxygen and triethylamine, in both solvents. This opens the door to many possible applications where entrapped dye molecules could be used as sensors in systems where the dye and surrounding solvent could have negative interactions.