Crystal Engineering of Binary Organic Eutectics: Significant Improvement in the Physicochemical Properties of Polycyclic Aromatic Hydrocarbons via the Computational and Mechanochemical Discovery of Composite Materials

Zeinab M Saeed,Sharmarke Mohamed,Hector H Hernandez,Abeer F Shunnar,Wegood M Awad,Bhausaheb Dhokale,Panče Naumov

doi:10.1021/acs.cgd.1c00420

Zeinab M Saeed, Sharmarke Mohamed + Show 5 more

Open Access

https://doi.org/10.1021/acs.cgd.1c00420

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Abstract

Derivatives of polycyclic aromatic hydrocarbons (PAHs) are widely used in optoelectronic materials. However, the poor solubility of unfunctionalized PAHs represents a challenge for the continued application of these compounds in emerging technologies. For organic compounds bearing one or more functional groups capable of engaging in directional hydrogen or halogen-bonding interactions, the crystal engineering toolkit currently offers many routes for optimizing the solid-state properties of these compounds. Such efforts typically lead to the discovery of periodic crystal forms that display strong adhesive intermolecular forces between the molecular fragments. By contrast, the crystal engineering of organic eutectic composites is relatively unexplored and poorly understood. Here, we report the mechanosynthesis and experimental characterization of the properties of three eutectic composites of pyrene (PYR) and anthracene (ANTH) that were discovered using the coformer bisphenol A (BPA) or phenothiazine (PTZ). The resulting eutectic composites (PYR-BPA, PYR-PTZ, and ANTH-PTZ) display significant melting point depressions ranging from 19 to 51 °C relative to the melting point of the PAH. The equilibrium solubilities of the composite materials were also observed to be 2–5 times greater than that of the PAH. The crystal engineering of eutectic solid forms is currently hampered by the lack of reliable empirical or theoretical tools for predicting their formation. A weighted Monte Carlo simulation was used to estimate the mixing energies and binding modes of a limited set of molecular pairs, leading to temperature-dependent interaction parameters that show promise in the selection of coformers with a high likelihood of forming eutectic composites. Complementary dispersion-corrected density functional theory (DFT-D) calculations on a set of PYR and ANTH composite models reveal that organic eutectic composites are not driven to form on the basis of favorable thermodynamics as evidenced by an average interaction energy of 2.60 kJ mol–1 across the series. Synthon incompatibility and molecular shape mismatch appear to be important factors to consider in targeting eutectic solid forms. This work paves the way for the systematic crystal engineering of organic eutectic solid forms with tunable physicochemical properties using a synergistic computational modeling and mechanosynthesis approach.

Highlights

Polycyclic aromatic hydrocarbons (PAHs) are a class of organic compounds that lack heteroatoms and feature two or more aromatic rings
Provided the organic molecule has one or more functional groups that can engage in directional hydrogen- or halogenbonding interactions, the crystallization of periodic multicomponent solid forms such as cocrystals,[14−18] salts,[19−21] ionic cocrystals,[22−26] or solvates[27,28] has been proven to be an effective crystal engineering strategy for optimizing the solubility and optical and mechanical properties of these
In the case of the PYR-bisphenol A (BPA) composite, mechanical grinding is only likely to break down the size of the crystallites without leading to new morphologies for the eutectic crystallites. These results indicate the importance of mechanical grinding as a preparative technique for eutectic discovery as the high shear forces and compressive impacts generated in a ball mill produce the necessary conditions for efficient chemical mixing and surface interactions needed to form the composite

Summary

INTRODUCTION

Polycyclic aromatic hydrocarbons (PAHs) are a class of organic compounds that lack heteroatoms and feature two or more aromatic rings. We demonstrate that both of these fundamental properties of PAHs solubility and melting point can be optimized using a complementary computational modeling and mechanochemical approach[33,34] for the discovery of binary eutectic composites (Scheme 1b). This is achieved using the coformer (Scheme 1a) bisphenol A (BPA) or phenothiazine (PTZ). This work expands the supramolecular toolkit and lays the foundations for the rational crystal engineering of organic eutectic composites using computational methods

RESULTS AND DISCUSSION

CONCLUSIONS

EXPERIMENTAL SECTION

■ ACKNOWLEDGMENTS

■ REFERENCES