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            In the first year, Justin Kumpfer worked on the synthesis of pyridone-based esters. It was found that while the substitution chemistry of pyridones was difficult, the species were capable of reacting through nucleophilic acyl substitutions. Metal-based coupling reactions proved problematic, as the pyridine functionality chelated the metal from the catalyst, rendering the reaction inert. These results provided the groundwork for the rest of the project. 

In the second year, David Witte synthesized a series of bis-functionalized pyridone terminated esters. Supramolecular polymers produced flexible, long-lived fibers pulled from the melt, but interestingly produced only a frustrated nematic phase observable only upon crash cooling the isotropic melt in liquid nitrogen. It is believed that the nematic phase could only be captured in this dramatic fashion because the overall structure of the assembled pyridone species would be too irregular to effectively form a mesogenic phase.

Also in the second year, a side project funded by this grant was carried out by Jason Greuel involving the investigation of the liquid crystalline properties of supramolecular networks. We observed the formation of a series of mesogenic networks with increasing netpoint inclusion. The mesogenic portions of these systems arise from a hydrogen bonded interaction between a bisbenzoic acid (tetraethyleneglycoxy-bis-4-benzoic acid, 4EOBBA), a rigid bispyridyl system (1,2-bis(4-pyridyl) ethylene), and a tetrafunctionalized non-mesogenic networking agent (tetrakis-4-pyrixyloxy methane, p-TPPE), which is used to introduce a network and disrupt liquid crystallinity. All the materials uses in this study are outlined in Figure 1. The networking agent was

Figure 2: Netpoint for Tris-network Study

added in increasing concentrations to the system. A smectic phase was observed in concentrations up to 8.5% of networking agent. The nematic phase was observed until concentrations up to 22.5%, which displayed a frustrated nematic phase, barely forming before crystallizing. At 25% and above, only melting and crystallization behavior was observed. It was curious to note that the cut-off for any liquid crystallinity (22.5%) which correspons closely with the tetra-functionalized nature of the crosslinking agent. This phenomenon may arise from a statistical correlation, where at 25%, one of the benzoic acid components would always be hydrogen bonded with one of the networking species, inhibiting the formation of the hydrogen bond with the rigid 2RP species, and therefore inhibiting the formation of the hydrogen bond.

A further study involved annealing these networks in the mesophase and observing a premature onset of crystallization. This onset rose to higher and higher temperatures with increasing netpoint inclusion. This phenomenon was not observed in small molecule covalent or supramolecular liquid crystals. The first study has produced a paper which will soon be submitted to Liquid Crystals, and the second manuscript is in development. Both will have two undergraduate authors.

Figure 3: Netpoints for Tris- and Bis- centered Network Study

As the pyridone project seemed to be at an end, producing systems barely mesogenic in nature, further investigation was carried out on the networked systems. In order to determine if the statistical correlation between the functionalty of the networking agent and the disappearance of the liquid crystalline phase exists, a tris-functionalized networking agent was synthesized as outlined in Figure 2. The networks so created displayed smectic phases until 15% concentration, and a complete destruction of mesogenicity (also a frustrated nematic phase) at 32%.           As a continuation of this work, a series of non-mesogenic bis pyridyl system was synthesized- as detailed in Figure 3. This work, carried out by Jason Greuel, Tim Andrews and Justin Wichman, involved the synthesis of the polymer-forming agent as well as its inclusion in the macromolecular systems. It was found that the this agent displayed liquid crystallinity when mixed with 4EOBBA and 2RP in loadings up to 25% (10% for the presence of smectic phases). This is markedly lower than the expected 50% based off of previously observed statistical correlations. It is believed that the markedly reduced melting point of the 2PD system is the principal contributor to the retardation of the transitions. The results of this work are being compiled into a publication which will have four undergraduate authors and will be submitted to Liquid Crystals.

Figure 4: Small Molecule Liquid Crystalline Materials

In order to determine if similar effects are observed in small-molecule, discrete liquid crystalline systems, similar complexes were made by Michael Zenner and Joshua Tessner utilizing 4-octyloxybenzoic acid as the hydrogen bond donor. The materials used in this portion of the study are outlined below in Figure 4. Complexes made using the C₈ Acid, 2RP and 4PD displayed liquid crystallinity in loadings of 4PD up to 99% that still displayed strong liquid crystalline characteristics. The extremely high loading of the disruptive 4PD into the complexes that retained liquid crystallinity was very surprising- it is surmised that the C₈ acid is forming mesogenic dimers in the presence of excess 4PD and a minimum

Figure 5: Distonic Mesogen Forming Agents

of 2RP. 3PD and 2PD containing systems display similar characteristics, with lower concentrations leading to the disruption of liquid crystallinity. Future work will involve changing the 2RP portion of the systems to a different, more flexible system. This proposed structure, seen in Figure 5, involves the formation of the stilbazole structure and coupling it onto a tri, tetra or pentaethyleneglycoxy chain. The effects of the increased flexibility of the mesogen-forming agents will be studied, as well as the effects of networking these systems into a larger macromolecule.