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

Abstract

Aggregation‐induced emission (AIE) luminogens are attractive dyes to probe polymer 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). Nonetheless, 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 using fluorescence lifetime as an absolute fluorescence parameter, it is demonstrated that this assumption can be invalid in many commonly encountered conditions. To this aim, different polymers are loaded with tetraphenylenethylene (TPE) and characterized during the application of thermal and mechanical stress and physical aging. Under these conditions, polymer matrix transparency variation is observed, possibly due to local changes in refractive index and to the formation of microfractures. By combining 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 photophysical properties of AIE dyes (RIM effect) or to alterations in the matrix optical properties.

Unveiling size‐fluorescence correlation of organic nanoparticles and its use in nanoparticle size determination

“…[14][15][16][17] Nanoparticles of different sizes can be easily obtained by adjusting the bis-UPy concentration in the precursor solution; (ii) aggregation-induced emission (AIE) features of TPE derivatives eliminate the ACQ effect in FNPs, rendering fluorescence signals highly bright. [18][19][20][21][22][23] On this basis, a logarithmic correlation between the fluorescence intensity and nanoparticle size is successfully established for nanoparticles of TPE-UPy, TPEPy-UPy, and TPEDC-UPy with a correlation coefficient higher than 0.96. Theoretical calculations demonstrate that the bis-UPys at the surface and within the interior of the nanoparticles have different molecular pack-ing environments, which greatly influence the nonradiative decay rates of the TPE derivatives.…”

Hybrid Encoding Strategy of Multi-Stimulus Response Aggregation-Induced Emission Hydrogels for Advanced Information Encryption and Safety

“…The photoluminescence properties of the system were also investigated. Obviously, a typical aggregation-induced luminescence can be observed as the system is subjected to UV irradiation (Figure a). , The PTO-1.5 hydrogel was injected into a mold and subsequently subjected to freeze–thawing to form the “FZU” shape. In addition, the as-prepared hydrogel (with a thickness of ∼1 mm) possessed adequate transmissivity (∼80%) in most visible light ranges (Figure b).…”

Effects of Plasticizers on Structural Transitions and Heterogeneity of Poly(vinyl alcohol) Films as Studied via AIE Materials

“…In the PVA film with 20% glycerol loading, the fluorescence gradient along the thickness direction can hardly be observed in the cross section. The recent work by Gualandi et al suggested a probability that light scattering will change the emission intensity of AIE luminogens during some common conditions like heating/cooling, stretching deformation, and physical aging, accompanied by polymer matrix transparency deterioration. However, the volatilizing PVA solutions as well as ultimately obtained films possessed high optical transparency, i.e., the transmittance within the visible-light range 400–800 nm preserved high as 90%.…”

“…In the PVA film with 20% glycerol loading, the fluorescence gradient along the thickness direction can hardly be observed in the cross section. The recent work by Gualandi et al 35 suggested a probability that light scattering will change the emission intensity of AIE During the evaporation of water, the mean concentrations of PVA in solutions (C m ) could be attained by a gravimetric analysis method. The slopes of MFI−thickness curves for both the skin layer and the core layer are plotted against C m , and the results are shown in Figures 2a and S3.…”