A straightforward way for the preparation of mechanochromic polymers consists of incorporating a suitable content of a mechanophore in the polymeric matrix either by physical dispersion or via covalent functionalization. Although covalent incorporation may require demanding chemical efforts, this approach can offer significant advantages over physical dispersion. In this work, a common thermoplastic elastomer, styrene-b-(ethylene-co-butylene)-b-styrene triblock copolymer grafted with maleic anhydride (SEBS-MAH), was covalently functionalized with 1-aminomethylpyrene (AMP). MAH functional groups are covalently linked to the ethylene-co-butylene blocks, thus allowing a precise and selective confinement of the chromogenic AMP units in the soft block. Flat, fully conjugated pyrene units undergo the reversible formation of π−π aggregates, readily distinguishable by their red-shifted emission. These aggregates were heavily affected by the application of mechanical stimuli. Despite the low degree of mechanophore functionalization (about 1 wt %), uniaxial deformation of the polymer was reliably monitored via fluorescence and a clear drop in the excimer to monomer emission ratio (I E /I M ) was observed starting from 50% of strain. The marked mechanochromism was confirmed by emission lifetime measurements and also by near-field investigations. In addition, the mechanoresponse showed good reversibility after repeated stress−relaxation cycles. Control experiments performed on formulations comprising a physical dispersion of pyrene in unfunctionalized SEBS showed faint excimer emission and a negligible mechanochromic response up to 5 wt % of doping, in substantial agreement with the scanning near-field optical microscopy analysis. An evident drop of the I E /I M ratio occurred for 10 wt % of pyrene, albeit the excimer emission remained predominant even at the highest deformation, being a smaller fraction of pyrene moieties involved. Overall, the covalent approach appeared as an elegant procedure to confine the chromogenic unit in the soft phase of block copolymers and thus to provide an elastomeric film showing a detectable and reversible mechanochromic response with a modest (i.e., ∼1 wt %) amount of pyrene molecules, i.e., 10 times smaller compared to the dispersed system.

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.

organic compounds made of two or more aromatic rings, fused together in linear, angular, or cluster arrangements. They can be also referred as low-molecular weight PAHs (two or three rings) and high-molecular weight PAHs (four or more rings). [3] These ubiquitous compounds can be generated from both anthropogenic activities, such as industrial, residential, and vehicular emissions, and natural pheno mena, i.e., open burning, volcanic activities, and spills from coal deposits. [2,3,[5][6][7] The occurrence of PAHs has been assessed worldwide in different aquatic systems including influents and effluents from wastewater treatment plants, groundwater, surfaceand sea-water. [3] Currently, over 400 PAHs and derivatives have been identified and classified, but most regulations, analyses, and data are focused on only 14 to 20 PAH compounds. [2,3,7] PAHs are well-known toxic, mutagenic, either carcinogenic or suspected carcinogenic compounds, accumulating in human and animal tissues. [2,3] These compounds are characterized by high hydrophobicity and good lipid solubility due to their aromatic and delocalized structure: when their molecular weight increases, their aqueous solubility diminishes, whereas resistance to oxidation and reduction rises. [2][3][4] PAHs absorption and bioaccumulation in several tissues, as well as their ubiquitous occurrence in the environment, pushed US EPA (United States Environmental Protection Agency) and EEA (European Environment Agency) to identify 24 PAH compounds as priority contaminants, thus introducing strict regulations for their monitoring. [8][9][10][11] The 16 PAHs considered as priority pollutants by US EPA are: naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benz[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, indeno[1,2,3-cd] pyrene, dibenz[a,h]anthracene, and benzo[ghi]perylene (Chart S1, Supporting Information). The European Union has set the maximum limit of 0.1 µg L −1 as sum of benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[ghi]perylene, and indeno [1,2,3-cd] pyrene in water for human consumption, with a particular attention to benzo[a]pyrene limited to 0.01 µg L −1 . [12] The removal of PAHs represents one of the current challenges in environmental chemistry. Methods are based on biodegradation, chemical, and physical removal processes, often combined in order to obtain the highest degree of PAHs removal. [2][3][4]6,7,13] Despite biological treatment methods have been proposed in municipal wastewaterThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/smll.202104946.

The photophysical behaviour of phosphorescent rigidification-induced emission (RIE) dyes is highly affected by their micro- and nanoenvironment. The lifetime measure of RIE dyes dispersed in polymers represents an effective approach...

The increasing interest for stimuli-responsive materials is transversal to a variety of application fields, ranging from medicine to automotive, from packaging to aerospace. Among the several combinations of external stimuli, materials and responses, polymeric mechanochromic materials displaying significant luminescence changes upon mechanical stimulation represent smart technological products offering stability and processability, but also sensitive, non-invasive and versatile diagnosis of mechanical stress. Yet, photophysical characterization of solid polymers – that can be optically dense matrixes, intensely coloured and highly scattering – requires special care to provide reliable and reproducible results. In this contribution we critically discuss the different aspects to consider for a successful quantification of optical properties of luminescent mechanoresponsive polymers, with an overview of the instrumental setup needed. Depending on the nature of their response, materials are classified into (i) intensity and (ii) spectrum-changing systems under mechanical stimuli, and the different approaches to obtain the luminescence variation are presented together with pros and cons of any strategy. The resulting general picture of the field gives a clear taste of the disruptive potential of these materials on a variety of applications.