Submicronization of organic compounds is a challenging requirement for applications in the imaging and pharmaceutical fields. A new Supercritical Anti-Solvent process with microreactor (µSAS) was developed for nanoparticle (NP) synthesis. Tetrahydrofuran (THF) was used to solubilize a model organic molecule, tetraphenylethylene, and supercritical carbon dioxide (sc-CO2) was used as antisolvent. The solubility of TPE in the THF/CO2 system was first measured by in situ experiments. Then, NPs of TPE were prepared in various experimental conditions and characterized by transmission electron microscopy (TEM). Chosen experimental conditions led to NPs with a mean size of 9 ± 3 nm. Experimental µSAS results were compared with size distributions obtained by simulation, to obtain surface tension values, which are difficult to access by experiment alone. Simulations coupling Computational Fluid Dynamics (CFD) and Population Balance Equation (PBE) were performed under turbulent conditions in the high pressure microreactors. This coupled experimental and theoretical approaches allowed a deep understanding of the µSAS process and underlined the superior value of this technique for the preparation of NPs.
Three styrylbenzoxazole derivatives with terminal dicyanomethylene group were studied in order to understand how minor modifications brought to the benzoxazole ring influence the photoluminescence properties. The three compounds were weakly fluorescent in organic solution because of molecular motions around the styryl single bonds. The unsubstituted (1) and methoxy (2) derivatives showed clear solid-state luminescence enhancement (SLE) properties. Distinct emission characteristics were attributed to the formation of amorphous and crystalline particles owing to scanning electron microscopy. These two compounds were also strongly luminescent as microcrystalline powders. Compound 1 that crystallized as slip stacks was a better emitter than the methoxy derivative 2, in which intermolecular interactions are more numerous, according to X-ray diffraction analysis. In contrast, compound 3 was virtually not emissive, confirming that in this series of dyes the presence of the hydroxy group is detrimental to PL emission, as rarely observed among SLE-active fluorophores.
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