Emission or scattering?Discriminating the origin of responsiveness in AIEgen-doped smart polymers using the TPE dye

Aggregation-induced emission(AIE)luminogens are attractive dyes to probe poly-mer properties that depend on changes in chain mobility and free volume.When embedded in polymers the restriction of intramolecular motion(RIM)can lead to their photoluminescence quantum yield(PLQY)strong enhancement if local microviscosity increases(lowering of chain mobility and free volume).Nonethe-less,measuring PLQY during stimuli,i.e.heat or mechanical stress,is technically challenging;thus,emission intensity is commonly used instead,assuming its direct correlation with the PLQY.Here,by usingfluorescence lifetime as an absolutefluorescence parameter,it is demonstrated that this assumption can be invalid in many commonly encountered conditions.To this aim,different poly-mers are loaded with tetraphenylenethylene(TPE)and characterized during the application of thermal and mechanical stress and physical aging.Under these con-ditions,polymer matrix transparency variation is observed,possibly due to local changes in refractive index and to the formation of microfractures.By combin-ing different characterization techniques,it is proved that scattering can affect the apparent emission intensity,while lifetime measurements can be used to ascertain whether the observed phenomenon is due to modifications of the photophysi-cal properties of AIE dyes(RIM effect)or to alterations in the matrix optical properties.