Tailoring ultrasound-induced growth of perylene diimide nanowire crystals from solution by modification with poly(3-hexyl thiophene).

Tailoring nanocrystalline morphologies of organic semiconductors holds importance for organic electronics due to the influence of crystal characteristics on optoelectronic properties. Soluble additives that control crystal growth are commonly found in a variety of contexts such as biomineralization, pharmaceutical processing, and food science, while the use of ultrasound to modify crystal nucleation and growth has been routinely employed in producing crystals of food ingredients, biomolecules, pharmaceuticals, and inorganic materials. However, both methods have been applied to the growth of organic semiconductor crystals only in limited fashion. Here, we combine these two approaches to show that colloidally stable nanowire suspensions of a n-type small molecule, perylene diimide (PDI), can be prepared with well-controlled structures by sonocrystallization in the presence of a p-type polymer, poly(3-hexyl thiophene) (P3HT), as a soluble additive. By preferentially adsorbing on lateral crystal faces, P3HT dramatically reduces PDI crystal growth rate in the lateral directions relative to that along the nanowire axis, yielding nanocrystals with widths below 20 nm and narrow width distributions. With the use of uniform short PDI nanowires as seeds and extension with metastable solutions, controlled growth of PDI nanowires by "living crystallization" is demonstrated, providing access to narrowed length distributions and tailored branched crystal morphologies.