Energy–Structure–Function Maps: Cartography for Materials Discovery

Abstract

bonding motif that dominates the lattice energy of the framework: that is, directional coordination bonds in the case of PCPs and MOFs, or covalent bonds for COFs. The dominance of a particular arrangement of interactions allows families of structurally related or "isoreticular" [4] frameworks to be prepared because the same bonding pattern can be assumed for multiple linkers. Hence, MOFs and COFs have become enormously popular platforms for a wide variety of materials applications, enabled by the relative ease with which one can explore the available "structure-function space." The importance of this transcends specific materials functions, such as porosity: isoreticular assembly is a powerful, generalizable tool to assemble molecular subunits in the solid state. [5] The situation is different for molecular crystals, which lack extended networks of coordination or covalent bonds. Despite much progress in the field of crystal engineering, [6] it is still rather challenging to program the assembly of molecules in crystalline solids. This is because the intermolecular forces that define molecular crystals-van der Waals and electrostatic interactions-are typically weaker and span a smaller energy range. Consequently, the lattice energies of molecular crystals are more evenly composed of various weak interactions and so the structure-directing forces are a more subtle balance than for PCPs, MOFs, and COFs. Strategies to make molecules crystallize more systematically, such as introducing strong hydrogen-bond donors and acceptors, can succeed but this may also introduce synthetic complexity. Moreover, the addition of such groups to create directional molecular building blocks, or "tectons," [7] can profoundly change the nature of the moleculefor example, by affecting its solubility or polarity-in ways that might not be aligned with the intended function. This can also be true for extended frameworks: in some PCPs and MOFs, the metal serves a specific chemical function, for example, as a catalyst, while in others, the metal is mostly there to hold the framework together-it serves no explicit chemical role.The introduction of directional functional groups such as carboxylic acids into organic tectons exemplifies the strategy of purposeful crystal engineering, whether this be in a hydrogenbonded molecular organic framework or in the organic linker of a MOF. Arguably, such intuitive design strategies will be defeated by complexity for molecular crystals, and even "wellbehaved" isoreticular extended frameworks might carry an unacknowledged overhead in terms of incorporating directing Some of the most successful approaches to structural design in materials chemistry have exploited strong directional bonds, whose geometric reliability lends predictability to solid-state assembly. For example, metal-organic frameworks are an important design platform in materials chemistry. By contrast, the structure of molecular crystals is defined by a balance of weaker intermolecular forces, and small changes to the molecular building b...

Evolutionary chemical space exploration for functional materials: computational organic semiconductor discovery

“…The result is an energy-structure-function (ESF) map for each molecule, describing the likely crystal structures, their energetic stability and properties. 5 As an example of their utility, ESF maps have guided the discovery of a set of unprecedentedly low density molecular crystals with high methane storage capacity. 6 In the eld of organic semiconductors, ESF maps have been used to investigate the effect of crystal packing types on calculated carrier mobility within families of azapentacene and pyrrolebased azaphenacene molecules.…”

Large-Scale Computational Screening of Molecular Organic Semiconductors Using Crystal Structure Prediction

“…12 A recent advance in the use of computational methods to guide the discovery of functional materials is the mapping of simulated properties onto the crystal energy landscape produced by CSP methods. [13][14][15] The result, which we refer to as the energy-structure-function (ESF) map of a molecule, 13 describes the possible crystal structures, their relative stabilities and expected properties. The assessment of ESF maps of candidate molecules for a targeted function can help rule out molecules with no (or only high energy) predicted structures with the required properties and prioritize the synthesis of molecules with promising predicted structures.…”

“…To our knowledge, this is the largest set of molecules that has been subjected to CSP and prop- Figure 1: The known (1) and hypothetical (2-28) molecules studied. Symmetrical (C 2v ) isomers (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16) are colored in orange, to contrast with the asymmetric (C s ) isomers (17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28).…”

The influence of nitrogen position on charge carrier mobility in enantiopure aza[6]helicene crystals

“…24 CSP has been combined with the prediction of optoelectronic properties to develop energystructure-function (ESF) maps. [25][26][27] These maps have been applied, for instance, to understand the impact of different packing on the charge mobility of unknown azapentacene derivatives. 26 The data confirmed that packings which maximized the π-π stacking interactions (sheet-like arrangements) also improved the charge transport and that these packings can be induced by C-H•••N bonding.…”