Sensitive and reliable detection of glass transition of polymers by fluorescent probes based on AIE luminogens

The glass transition of polymers is an immensely-used yet less-understood phenomenon concerning the dynamics of polymer chains in bulk or in confined surroundings, which dictates directly their performances in engineering sectors. Monitoring of the glass transitions or dynamics of polymers is hampered by the lack of facile yet robust methodologies. Herein, we developed a sensitive, reliable and straightforward approach for the detection of glass transitions of polymers using fluorescent probes based on aggregation induced emission (AIE) luminogens. Fluorescence emission of polymers doped with AIE luminogens, including tetraphenylethene (TPE) or its derivatives, showed a sensitive response to the glass transitions of polymers. The sensitivity of fluorescence to glass transition could be optimized by increasing TPE loading. Fluorescence intensity of TPE-doped polymers dropped as much as 25 fold with increasing temperature in the investigated range. The temperature dependence of the fluorescence intensity gave rise to the straightforward determination of the glass transitions of the polymers. Moreover, it is worth mentioning that simply mixing AIE luminogens with polymers, rather than covalently labeling, is possible due to the AIE characteristics of the probes. This significantly facilitated measurements. Given the significant advantages of AIE luminogens as probes, including high and tunable sensitivity, immunity to aggregation, facile operation and simple data processing, fluorescence techniques based on AIE luminogens offer new access for the investigation of the glass dynamics of polymer chains in confined spaces.