(321b) Graphoepitaxy-Directed Crystallization of Small-Molecule Organic Semiconductors into 3D Structures

In this work, we apply the principle of graphoepitaxy to guide the solution-phase crystallization of model semiconducting perylene within nanopillar silicon grids. Graphoepitaxy-directed oriented growth of molecular crystals has previously been demonstrated through the matching of angles presented by surface relief structures to specific angles between crystallographic planes of molecular crystals. In contrast, our method relies on registry between the underlying grid periodicity and the overall shape of perylene crystals, which grow as flat plates. When nucleated within the nanopillar grids, perylene crystals adopted two distinct in-plane orientations in which the plates align either with the unconfined rows or columns between nanopillars. Ostwald ripening at the air/liquid/grid interface to dissolve smaller, misoriented crystals while enlarging crystals aligned with the grid structure resulted in the formation of three-dimensional trellises of single crystals meeting at 90^o angles. Building on our previous discovery of nanoporous scaffold-directed assembly of needlelike triisopropylsilylethynyl pyranthrene crystals into vertical crystal arrays[1], our findings point to the possibility of assembling single crystals into complex structures through judicious grid design for different crystal morphologies across materials classes. Critically, the high-energy p-planes of perylene crystals are exposed at the grid surface, which will have important implications for controlling material properties, from reactivity to dissolution rates.

[1] K. Zong,Y. Ma, K. Shayan, J. Ly, E. Renjilian, C. Hu, S. Strauf, A. Briseño, and S.S. Lee. “Directing Solution-Phase Nucleation to Form Organic Semiconductor Vertical Crystal Arrays.” Crystal Growth & Design 19, (2019): 3461–3468.