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.

Red-emitting tetraphenylethylene derivative with aggregation-induced enhanced emission for luminescent solar concentrators:A combined experimental and density functional theory study

This study examines the use of an aggregation-induced enhanced emission fluorophore(TPE-MRh)to prepare red-emitting luminescent solar concentrators(LSCs)based on poly(methyl methacrylate)(PMMA)and poly(cyclohexyl methacrylate)(PCMA).TPE-MRh is a tetraphenylethylene(TPE)derivative bearing two dimethylamino push groups and a 3-methyl-rhodanine pull moiety,with absorption maxima at around 500 nm and fluorescence peak at 700 nm that strongly increases in solid-state.TPE-MRh displays a typical crystallizationinduced enhanced emission that has been rationalized by modeling the compound behavior in solution and solid-state via density functional theory calculations with the inclusion of the environment.TPE-MRh dispersed into 5×5 cm2 polymer films with a thickness of 25±5μm has revealed a partial fluorescence quenching with fluorophore content.Quantum yields(QYs)below 10%for the 2 wt.%of doping have been addressed to the formation of less emissive micro-sized clusters of fluorophores.PMMA slabs with the same surface size but 3 mm of thickness and 200 ppm of TPE-MRh have provided QY of 36.5%thanks to the attenuation of the detrimental effects of fluorophore aggregation.This feature is reflected in the LSCs performance,with devices achieving the largest power collected by the photovoltaic cell.