Biosourced Materials

This study introduces a new nanocrystallization method assisted by ultrasounds that produces needles or nanocubes of CMONS, a stilbene dye, with excellent control over polymorphism and narrow size distribution. Owing to the production of radicals from dissolved dioxygen by high-intensity ultrasounds, trans-to-cis isomerization was observed in the absence of nitrogen bubbling, with the formation of two distinct crystalline phases for different diastereomers. The crystallinity of CMONS needles was probed by various techniques, including X-ray and electron diffractions, fluorescence spectroscopy, and dynamic nuclear polarization (DNP)-enhanced solid-state nuclear magnetic resonance. The latter was used to hyperpolarize 1H nuclei and to record 1H-13C and 1H-15N CPMAS NMR spectra at natural isotopic abundance with a very high signal-to-noise ratio. With such sensitivity, one can easily discriminate between cis and trans-I forms of CMONS, detect the presence of multiple polymorphic phases (even with minor contributions), and check the absence of an amorphous phase. Finally, the mechanism involved in the formation of CMONS needles was ascertained after stabilizing intermediate nanocubes against Ostwald ripening and ordered aggregation mechanisms using the CTAB surfactant.