Blinking of single dye molecules in a polymer matrix is correlated with free volume in polymers

Blinking of single cyanine (DiI) molecules dispersed in poly(methyl acrylate) and in a series of poly(alkyl methacrylate) matrices is reported. The blinking dynamics is characterized by relaxation times obtained from the decay of autocorrelation function of individual DiI molecules. The mean relaxation times are independent of the polymer composition, molecular weight or the temperature. On the other hand, we observed a systematic increase of the fraction of molecules that show the blinking with increasing temperature difference T − Tg (Tg being the glass transition temperature). The results are discussed in terms of an increase of free volume around DiI molecules with increasing temperature.