Aggregation Induced Emission: new emerging fluorophores for environmental sensing

PMMA films containing tetraphenylethylene (TPE) derivatives as red-emissive AIE fluorophores (AIEgen) were demonstrated to be sensitive to both volatile organic compounds (VOCs) and thermal stress. Notably, a novel AIE fluorophore (TPE_RED) was synthesized and used as the initiator to prepare red-emitting poly(methyl methacrylate) polymers (PMMA_TPE_RED1.5) via atom transfer radical polymerization (ATRP). The sensing performances of the spin-coated films (thickness of 2 μm) demonstrated significant vapochromism when exposed to VOCs characterized by high vapour pressure and favourable interaction with the polymer matrix. It was worth noting that PMMA_TPE_RED1.5 displayed substantial vapochromism already at concentration of CHCl3 vapours of 40 ppm, that is about 4 times smaller than those ever registered in our laboratory with the same apparatus. This threshold was even more decreased in the case of PMMA films containing the TPE_RED physically mixed or another TPE-based derivative already tested in literature, i.e. the barbituric acid-functionalized tetraphenylethene derivative (TPE-HPh-Bar). PMMA films containing TPE_RED AIEgen resulted also sensitive to temperature variations showing an evident thermochromic response close to the glass transition temperature of the polymer matrix.