This project focuses on the design and synthesis of molecular-based functional materials. Inclusion compounds based on lamellar guanidinium-organodisulfonate host frameworks, in which organodisulfonate "pillars" connect opposing hydrogen-bonded sheets of guanidinium cations (G) and sulfonate moieties (S) to generate inclusion cavities, exhibit a extraordinary capacity in this regard owing to the structural robustness of the GS sheet, which serves as a "supramolecular building block." The project will emphasize the synthesis of customized GS host frameworks endowed with inclusion cavities designed for specific recognition of select guest molecules and controlled ordering of functional guest molecules. The work will also capitalize on our recent discovery of lamellar GS inclusion compounds based on organomonosulfonates, and our even more surprising discovery of cylindrical inclusion compounds, wherein quasihexagonal guanidinium-organomonosulfonate sheets wrap around templating guest molecules to form hydrogen bonded "nanotubes." Specific objectives of this work include: (i) the synthesis of chiral GS hosts derived from a diverse library of chiral organodisulfonate pillars, with the aim of developing hosts for enantioselective separations of chiral compounds and probing the transmission of chirality in the solid state; (ii) the synthesis of polar host frameworks through assembly guided by asymmetric and banana-shaped pillars and examination of the effect of host structure on guest ordering; (iii) elucidation of the factors responsible for lamellae-cylinder isomerism in guanidinium organomonosulfonates, including the role of packing frustration, a concept often used in surfactant and block copolymer microstructures; (iv) the synthesis of robust hydrogen-bonded cylinders through tessellation with trisulfonates; and (v) completion of work aimed at elucidating the structure and properties of new thermotropic liquid crystal phases derived from guanidinium organomonosulfonates. Several mechanisms exist to ensure broad impact of this project, including (i) through the UMN Materials Research Science and Engineering Center, summer research experiences for undergraduates and teachers, many from minority-serving institutions, and the development of curriculum tools for high school teachers revolving around crystal structure, (ii) mentoring opportunities for graduate students and postdocs, (iii) several collaborations with scientists from other U.S. and international institutions, including visiting graduate students from Korean institutions sponsored by the Brain Korea-21 (BK-21) program, (iv) seminar visits to four-year colleges in the Midwest Association of Chemistry Teachers in Liberal Arts Colleges (MACTLAC), (vi) dissemination of outcomes to the scientific community through publications, conferences, and postings on our group web site, and (vii) anticipated publication of a manuscript (invited) in the Journal of Chemical Education on the topic of "designer crystals," accompanied by electronic media for visualizing self-assembly and crystal structures. %%% One of the foremost challenges in solid state chemistry is the design and synthesis of organic crystals - molecules assembled in lattices - with prescribed architectures, a discipline often referred to as "crystal engineering." This research employs molecules as "tinkertoys" that are designed to form open crystal frameworks that in many ways resemble prefabricated buildings containing empty offices equipped for occupation by functional items, in our case "guest" molecules having some useful property or function. In addition to exploring the fundamental principles underlying the guided assembly of molecules into crystal lattices, particular targets of this research include frameworks able to separate chiral isomers, which constitute a $100 billion component of the U.S. pharmaceutical industry, organic materials capable of doubling the frequency of light that may find potential applications in telecommunication technologies, and new composites of designer crystals and polymers that can provide lightweight but mechanically strong plastics with possible applications in the automotive and food packaging industries. The molecular nature of these materials offers substantial advantages in each of these applications with respect to either more improved properties or reduced processing costs. The achievement of these aims can have substantial impact on public health and key technologies that are vital to the U.S. economy. The research is also designed to equip emerging young scientists and engineers with the skills required to tackle new challenges in materials research while enhancing international interactions, particularly with key institutions and students from notable academic institutions in South Korea. This project is co-funded by the Division of Materials Research and the Chemistry Division.
