Control of Fullerene Crystallization from 2D to 3D through Combined Solvent and Template Effects

Abstract

Achieving precise control of molecular self-assembly to form designed three-dimensional (3D) structures is a major goal in nanoscale science and technology. Using scanning tunnelling microscopy and density functional theory calculations, we show that a 2D covalent organic framework (COF-1) can template solution-processed C guest molecules to form several solvent-dependent structural arrangements and morphologies via a 2D to 3D growth process. When 1,2,4-tricholorobenzene is used as solvent, C molecules form a template-defined close-packed structure. When heptanoic acid is used as solvent, a range of lower density architectures that deviate from the template-defined close packing are observed. We attribute this difference to the co-adsorption of the heptanoic acid solvent molecules, which is only achieved in the presence of the template. This work demonstrates the possibility to precisely control 3D molecular self-assembly through the synergistic combination of template and solvent effects.

Planar Anchoring of C70 Liquid Crystals Using a Covalent Organic Framework Template

“…Figure a shows an image where a small defect region was identified in a lattice of C 70 /COF‐1. This allows us to use geometric considerations to identify this lattice as a parallel‐shifted R‐layer (Figure c) . A similar shift geometry was observed for C 60 and explained by a template‐induced solvent co‐adsorption effect within the T‐layer.…”

“…In previous work, we have shown that the R1 layer C 60 molecule can shift with respect to the given T‐layer C 60 , which exists in threefold symmetry, forming a less‐dense molecular packing. The shifted positions were found to be stable states explained by a template‐induced solvent coadsorption effect . The same argument can also be applied for C 70 , where the co‐adsorbed solvent molecules are correspondingly observed (Figure S5, Supporting Information).…”

“…After introducing the C 70 solution, molecules can be observed in a number of adsorption sites: the top‐site (T), defined as adsorbed over boroxine ring; the pore‐site (P), defined as adsorbed in pore, and the pore‐top bilayer (P‐T), defined as co‐adsorption of P‐site and T‐site. The observed architectures are similar to those of C 60 in COF‐1, but with additional distinction of polymorphs based on the molecular anisotropy . The formation of different architectures of C 70 can be rationalized as arising from kinetic effect.…”

“…In addition, at domain edges, a T‐layer domain with a different orientation (β−2 phase) is visible, as shown in the magnified image (Figure d,e). This observation is enabled by the removal of two T‐site C 70 molecules (black ellipsoids in Figure a) by the STM tip, which suggests that the stability of the adsorbed molecules is compromised where the lattice is incomplete . A proposed T‐layer model is shown in Figure b.…”

“…Using a template to control guest molecular deposition and layer structure is a well‐established approach in surface science . However, this kind of template‐guided growth is rare in 2D or 3D crystalline engineering . In particular, the introduction of anchoring conditions by a monolayer host template has not yet been explored in LC growth.…”