Impact of the Aryl Amphiphile Hydrophobe Size on Controlling the π-Conjugated Microcrystal Growth along the π-Stack Direction

Morphology of organic π-conjugated microcrystals (MCs) controls the direction of light-guided, emission intensity, lasing threshold, and optical losses in the organic π-conjugated MCs. Control over π-stacking interactions during the MC growth provides control over the MC growth morphology, but it is a challenging task, and so far, there are no reported strategies toward this. Recently, we have shown that a binaphthyl aryl amphiphile retards the perylene MC growth along the CH-π stacking direction and results in novel square rod-shaped MCs with a unique waveguiding behavior. To further gain insights into the role of aryl amphiphiles on the growth process, in this work, the impact of four aryl amphiphiles with an increasing aryl amphiphile hydrophobe size on the perylene MC growth and morphology is studied. Depending on the aryl hydrophobe size, morphology directors (MoDs) either selectively retard the perylene CH-π stacking direction or retard both the CH-π stacking and weak edge-to-edge packing directions, resulting in square-rod or pseudo-cube-shaped MCs, respectively. The novel perylene MCs display shape-dependent UV–vis absorption and emission properties. Simulations are performed to calculate the MoD-facet binding energies and to rationalize the growth process. Systematic studies will pave the way to rationally design aryl amphiphile MoDs and predictively synthesize the π-conjugated MCs of diverse morphologies.