Molecular co-crystals: Semiconductors, photoactive solids, and catalysts

The unique properties of the organic solid state are derived from the close-packed, uniform arrangement of the molecules. Thus, control of molecular arrangement leads to control of solid-state properties. This thesis focuses on the use of co-crystals as tools to control molecular orientation. The approach utilizes intermolecular hydrogen bonds to enforce the arrangement of molecules within the co-crystal. The organization of molecules within designed arrangements provides structures that are used as organic semiconductors, photoactive solids and catalysts.;The ability to enforce the face-to-face stacking of aromatic molecules is important in the context of organic semiconductor solids. Typically, aromatic molecules pack within a herringbone arrangement, owing to edge-to-face interactions. However, the use of semiconductor co-crystal formers (SCCFs) provides solids with an enforced face-to-face arrangement of the semiconductor building blocks (SBBs). Specifically, the co-crystallization of a ditopic SCCF, based on resorcinol, with a SBB functionalized with pyridine "handle" groups results in the formation of a dimeric face-to-face arrangement of the SBBs. However, SCCFs based on resorcinol do not enforce the extended packing desired for organic semiconductors. The design of SCCFs based on 3-aminophenol, and handle groups based on pyridine-N-oxides provides an increase in extended face-to-face stacking between the SBBs.;The co-crystallization of SBBs with SCCFs leads to dimeric assemblies with handle groups in a parallel orientation. Thus, the synthesis of SBBs functionalized with olefin-based handles can introduce solid-state photoreactivity within the SBB assembly. The irradiation of such assemblies with UV light can result in a [2+2] photodimerization. Achieving photoactive solids with semiconductor groups is important for photopatterning of single-crystals and in the context of molecular targets.;The use of co-crystals to achieve the [2+2] photodimerization of olefins in the solid state provides access to molecules difficult to synthesize through solution phase chemistry. However, previously, [2+2] photodimerization required a stoichiometric amount of the components. We demonstrate that a catalytic amount of the co-crystal former may be used to direct quantitative yields of the photodimerization within the solid state with turnover accomplished through mechanochemistry.