Single Molecule Experiments on Small Molecule Glass Formers

We are using single molecule fluorescence microscopy to investigate dynamics near the glass transition in molecular fluids. Dynamics in this temperature regime are characterized by heterogeneities that are presumably only a few nanometers in size -- much too small to probe directly using traditional techniques. By tracking the movement of single embedded fluorophores, however, we can interrogate the system on a length scale comparable to the heterogeneities themselves.

We embed low concentrations of guest fluorophores in samples of molecular glass formers (such as glycerol and o-terphenyl). By monitoring the polarization of the emitted fluorescence from each guest molecule we can determine its orientation as a function of time, giving us a measure of local dynamics. However, we must remain cognizant of the fact that the probe we are using may induce some changes in the system behavior that we are trying to measure. To understand the importance of this effect, we endeavor to study a series of fluorophores embedded within a single glass former and a single fluorophore embedded in a series of glass formers.

Experimental setup and image of fluorescence from rubrene molecules embedded in glycerol at 204 K (Tg+14). The ratio of the intensities from the s- and p- polarization images can be used to calculate the orientation of each molecule

Would you like to learn more? If so, contact Stephan Mackowiak.