Unveiling the potential of solid-state chemistry: breakthroughs in organic synthesis and supramolecular chemistry

Chemical reactions can be carried out either in solvent (e.g., water, alcohols, benzene, etc.) or in the absence of solvents (i.e., solid state). A solvent-free medium is a powerful and environmentally friendly means to perform important chemical transformations. Advantages of solvent-free chemistry include increased efficiency, decreased cost, and minimization of toxic waste generation. Properties, such as reactivity of molecules in solids depend on how molecules are arranged in three-dimensional (3D) space on the molecular level, also referred to as crystal packing arrangements. Previous research from our group has concluded that if a crystal packing arrangement is inappropriate for an intended solid-state reaction, then addition of suitable complementary molecules (i.e. guest molecules) can alter the crystal packing in favor of that reaction. In this sense, specific non-covalent interactions between host and guest molecules can favor reactive crystal packing.

The research described in this thesis focuses on the design and synthesis of different molecules that participate in suitable non-covalent interactions between host and targeted complementary reactant molecules.

Mechanochemistry (i.e. chemistry by means of mechanical force) is a rapidly emerging area in the field of chemistry that is used for synthesis of nanomaterials, polymers, and pharmaceutical compounds. The first solid-state project focuses on demonstrating the versatility of mechanochemical energy (i.e. mechanical grinding) in achieving multi-step reactivity in a crystalline powder in just one reaction pot, thus furnishing easy access and improved yields in targeted organic reactions. This research will open new perspectives in mechanochemistry including improved efficiency of environmentally friendly industrial-scale reactions.

In line with investigating the physical properties of solids generated from a crystal engineering approach, a second project focuses on modifying the fluorescent properties of IsoH by introducing different guest molecules into the crystal lattice. Isocoumarin is a natural substance found in many plants and is associated with pharmacological properties. Additionally, isocoumarin has fluorescent properties suitable for dye applications. However, isocoumarin fluorescence is not as bright as other dyes available on the market. By introducing guest molecules into the crystal packing of an IsoH, the fluorescent properties of resulting solids exhibit enhanced optical properties. These results demonstrate one of the first crystal engineering approaches to systematically change the fluorescence properties of isocoumarin-containing solids.

In the context of designing functional solids, properties of materials depend on how molecules are arranged at an atomic level. In this sense, reactivity of solids can be extended to solid-state click reactions. Click reactions encompass a class of biocompatible reactions often used to join a substrate of choice with specific biomolecule (e.g. DNA or proteins to a fluorescent probe A click reaction involves addition of two functionalities, specifically an azide and alkyne. Thus, project focuses on design of azide and alkyne containing molecules which will arrange into a solid that enables reactivity between the two groups and thus, shining UV light on the resulting crystals enable targeted synthesis. With this project, we are trying to develop new reactions in solid-state mediam.