Characterizing the Structure of Organic Molecules of Intrinsic Microporosity by Molecular Simulations and X-ray Scattering

Abstract

The design of a new class of materials, called organic molecules of intrinsic microporosity (OMIMs), incorporates awkward, concave shapes to prevent efficient packing of molecules, resulting in microporosity. This work presents predictive molecular simulations and experimental wide-angle X-ray scattering (WAXS) for a series of biphenyl-core OMIMs with varying end-group geometries. Development of the utilized simulation protocol was based on comparison of several simulation methods to WAXS patterns. In addition, examination of the simulated structures has facilitated the assignment of WAXS features to specific intra- and intermolecular distances, making this a useful tool for characterizing the packing behavior of this class of materials. Analysis of the simulations suggested that OMIMs had greater microporosity when the molecules were the most shape-persistent, which required rigid structures and bulky end groups. The simulation protocol presented here allows for predictive, presynthesis screening of OMIMs and similar complex molecules to enhance understanding of their structures and aid in future design efforts.

Application of computational methods to the design and characterisation of porous molecular materials

“…63 This molecular simulation methodology has been used to generate the structures for a number of PMMs to predict and understand their pore structure. Abbott et al reported the amorphous structure of 22 organic molecules of intrinsic microporosity 64 (OMIMs) with variations of functionality at the core and periphery (end-groups). 61 The simulations identified a number of structure-property relationships that lead to greater porosity.…”

“…Importantly, the simulations described above show good agreement to empirical data, including gas adsorption. 23,64 Accordingly, simulations can be viewed as an essential tool for atomistic understanding of the properties of amorphous materials, such as the origin of porosity, that are not easily unobtainable by experimental methods alone.…”

Triptycene End-Capped Quinoxalinophenanthrophenazines with Aromatic Substituents – Synthesis, Characterization, and Single-Crystal Structure Analysis

“…13,14 As mentioned already, π-stacking is unfortunately less directional than other supramolecular motifs and therefore ideal arrangements are more difficult to achieve. [9][10][11] During our initial work on organic molecules with intrinsic microporosities, [15][16][17][18][19][20][21][22] we observed a hexagonal packing of D 3h -symmetric triptycene-based large quinoxalinophenanthrophenazines (QPPs) via an unusual strong π-π interaction of the QPP blades with those of adjacent QPP molecules. 23 This packing motif could only be broken by triptycene-end-capping.…”

Shedding Light on Structure–Property Relationships for Conjugated Microporous Polymers: The Importance of Rings and Strain

“…Structural hypotheses and models 14 aside, it is essentially unknown if CMPs, CTFs, and PAFs can be best described as highly branched polymers or as extended networks, or even as small but insoluble oligomers, which might nonetheless exhibit permanent microporosity. 18 This uncertainty over structure mainly stems from the amorphous or poorly crystalline nature of the experimental samples, coupled with their total lack of solubility. However, the need to understand structure–property relationships is highlighted by the recent discovery of new porous materials, such as soluble, hyperbranched CMPs and porous dendrimers, 19 organic molecules of intrinsic microporosity, 18 and other discrete organic molecules 20−24 that can show high levels of microporosity in the amorphous, solid state.…”