Determination of Glass Transition Temperatures in Bulk and Micellar Nanoconfined Polymers Using Fluorescent Molecular Rotors as Probes for Changes in Free Volume

Fluorescent molecular rotors embedded in polymer matrices can probe the local changes in the dynamics of the polymer matrix (such as the glass transition of polymers near interfaces/surfaces) that are not accessible from macroscopic measurements. Yet, there is little consensus as to how the fluorescence data should be analyzed, what property the fluorescence intensity actually represents, and what are appropriate/optimal rotors for glass transition measurements. By experimentation with a model fluorescent rotor, farnesyl-(2-carboxy-2-cyanovinyl)-julolidine (FCVJ), and also re-analysis of data available in the literature for other types of molecular rotors, we investigated the correlation between the relaxation processes of photo-excited rotors and free volume changes in matrix polymers. The temperature dependences of the fluorescence intensities from FCVJ-doped polystyrene (PS), poly(vin…