A synthetic pathway is described to construct "in bulk" two-dimensional (2D) polymers shaped as molecular sheets. A chiral oligomeric precursor is used that contains two reactive sites, a polymerizable group at one terminus and a reactive stereogenic center near the middle of the molecule. The bulk reaction yields bilayer 2D polymers of molecular weight in the order of millions and a monodisperse thickness of 50.2 angstroms. The 2D molecular objects form through molecular recognition by the oligomers, which self-organize into layers that place the reactive groups within specific planes. The oligomers become catenated by two different stitching reactions involving the reactive sites. At room temperature, stacks of these molecular objects can organize as single crystals and at higher temperatures melt into smectic liquid crystals. Nonlinear optical experiments reveal that solid films containing the 2D polymers form structures that are thermally and temporally more stable than those containing analogous 1D polymers. This observation suggests that the transformation of common polymers from a 1D to a 2D architecture may produce generations of organic materials with improved properties.

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This manuscript describes the bulk synthesis of shape persistent two-dimensional (2D) polymers using the self-assembly of rigid precursor molecules into bilayers. A precursor was synthesized with a structure that encodes for the necessary molecular recognition events to form bilayers with intemal orientational order. These events include homochiral interactions and confine reactive functions to planes leading to covalent stitching of flat polymers. The resulting molecular objects have a monodisperse thickness of 5 nm and polydisperse planar dimensions on the order of hundreds or thousands of nanometers. One of the stiching reactions, the oligomerization of acrylate groups to form an all-carbon backbone, is catalyzed by the presence of dipolar stereocenters 13 atoms away from the double bond. These enantiomerically enriched stereocenters are substituted by nitrile groups which react to generate the second stitching backbone of the plate-shaped molecules. A computer simulation indicates that 2D polymers of molar mass in the range of millions can be formed with extremely short stitching backbones provided planar confinement of functions is achieved by molecular recognition events. "Bulk" syntheses of shape persistent 2D polymers which do not require extemal boundaries to confine monomers into 2D spaces may lead to many interesting advanced materials.

A diacetylene monomer with a rigid backbone and capable of forming hydrogen bonds was synthesized and found to polymerize forming two-dimensional supramolecular assemblies. The twodimensional structure self-assembles when UV light generates polydiacetylene comb polymers, and hydrogen bonds are established within molecular layers. The two-dimensional assemblies have been characterized by X-ray diffraction and infrared spectroscopy and found to consist of highly ordered bilayers. The material forms blue solid thin films which generate third-order nonlinear optical signals and have remarkable photochemical stability to 1064 nm radiation from a Q-switched Nd:YAG laser. Upon heating to 62 °C, the material turns bright red reversibly while maintaining its two-dimensional structure, and this thermochromic process is accompanied by endothermic and exothermic signatures detected by differential scanning calorimetry. Most importantly, however, variable temperature sum frequency generation experiments show that the third-harmonic generation signals retain much of their original intensity through the thermochromic transitions. These results do not conform in a consistent manner to both the theory of third-order effects and the previously suggested connection between intramolecular conjugation and optical absorption of polydiacetylenes. It is therefore possible that intermolecular interactions in these highly ordered structures play a role in defining optical properties.

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