Nanomaterials made by the self-assembly of organic molecules are interesting due to their low processing costs and tunable electronic and optical properties. Since the size and shape of the nanomaterials strongly affect these properties, the ability to control the particles’ morphology would be useful.

Raquel Giménez, Teresa Sierra, University of Zaragoza, Spain, Enrique Ortí, University of Valencia, Spain, and colleagues have developed a method to control the morphology and emission properties of aggregates formed by star-shaped fluorescent compounds based on the 2,4,6‐tris(1,2,3‐triazol‐4‐yl)‐1,3,5‐triazine (TTT) moiety. The compounds used are the T3C₄ and TB3C₄ (pictured) TTT derivatives, which differ in the chains attached to the central triazole ring. They behave differently in their self‐assembly and their fluorescent properties.

T3C₄ and TB3C₄ were prepared by a reprecipitation method. Simple variations in some preparation parameters, such as the selection of the solvent/non‐solvent pair or the relative amount of both solvents, lead to a variety of aggregate shapes, such as spherical particles, one-hole hollow spheres, toroids, twisted fibers, and helical nanotubes in a controlled way (examples pictured). The various morphologies have a significant impact on the optical behavior.

The two derivatives allowed the study of the effect of the chemical structure on the aggregation and the optical properties. Compared to T3C₄, the introduction of an additional benzoyloxy moiety with the ability to rotate in TB3C₄ completely changed the emissive behavior. Interestingly, aggregation has opposite effects on the fluorescent properties of the two compounds: T3C₄ acts as a conventional fluorescent molecule, showing an aggregation-caused quenching effect, while TB3C₄ shows aggregation-induced emission (AIE).

• Self-assembly of Clicked Star-Shaped Triazines into Functional Nanostructures,
  Martín Castillo-Vallés, Eduardo Beltrán, Jesús Cerdá, Juan Aragó, Pilar Romero, José Luis Serrano, Enrique Ortí, Raquel Giménez, Teresa Sierra,
  ChemNanoMat 2018.
  https://doi.org/10.1002/cnma.201800484