Highly branched organic microcrystals via self-organization and growth kinetics manipulation

Abstract

We demonstrate the first investigation of highly branched small-molecular organic microcrystals via self-organization of crystallites at the nucleation stage and then growth kinetics manipulation at the crystal growth stage. Temperature control was found to be critical in the formation of the branched structures. At higher temperature (25 °C), crystallites follow the conventional growth route to minimize the total surface energy under thermodynamic control, and grow into polyhedral crystals. While at lower temperature (15 °C), crystallites would follow the reversed crystal growth route and preferentially self-aggregate into well-defined cage-like cubes. The branched octapod-shaped microcrystals are formed with nucleation at 15 °C for crystallites to self-organize into cube-within-cube aggregates, and then subsequent anistropic overgrowth from each corner of eight cubes at 25 °C. The higher growth rate along <111> directions induces the formation of the octapod structures. Surfactant was also found to encourage the secondary branching on the octapod-shaped architectures. This work provides a simple approach to synthesize organic microcrystals with a highly branched structure, which are expected to be useful as building blocks in nanoelectronics and nanocircuits.