Seed-Induced Pathway Control of Low-Dispersity Polymorphic Microcrystals of pi-Conjugated Molecules

The precise synthesis of polymorphic π-conjugated micro- and nanocrystals remains challenging due to the existence of competing assembled pathways. Here we realize controlled polymorphic microcrystals of a dicyanodistyrylbenzene derivative (A) via a seed-induced pathway transformation. Small-sized α-A nanocrystals that are thermodynamically stable are prepared via a microspacing physical vapor transport (PVT) method. These vapor-grown nanocrystals function as seeds and tailor the assembled pathway of potentially occurring β-A microcrystals corresponding to kinetically metastable products, leading to the controlled growth of α-A microcrystals. Intriguingly, the length and surface area of the seed-induced α-A microcrystals increase linearly with the molar ratios of the added monomer to seeds. Such a seed-induced transformation strategy resembles living supramolecular polymerization of amphiphilic dyes, which is also applicable to more polymorphic π-conjugated microcrystals even binary alloys. This work provides deeper insights in controlling assembled pathways and polymorphs of π-conjugated systems and producing organic microcrystals of narrow size distributions.