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Supramolecular Self-Assembly for Functional Multicomponent Structures

Paulo S Costa, University of Nebraska - Lincoln

Abstract

This thesis explores synthesis strategies towards multicomponent organic nanostructures. The primary goal is to study how the physical properties of these structures emerge due to the formation of cocrystals, mixes, and heterojunctions. ^ First, the self-assembly of molecules with bulk ferroelectric properties is studied on three noble metal surfaces. It is found benzimidazole forms one-dimensional hydrogen-bonded polarized chains on Au(111) and Ag(111) substrates. In order to probe the polarization direction of hydrogen-bonded chains, the basic molecule 5,5’-dimethyl-2,2’-dipyridyl is used as an indicator to point out which end of 3-hydroxyphenalenone chains terminate with a hydrogen. ^ The study of the structure formation of proton transfer organic ferroelectrics is expanded upon to include studies of the cocrystal formation from two different molecules. The goal is to manipulate the potential energy surface for proton transfer along the hydrogen bond. It is found that on Au(111), croconic acid forms cocrystals with both 5,5’-dimethyl-2,2’-dipyridyl and benzimidazole. ^ In a related effort, the dipoles of small molecules are exploited to perturb the spin crossover properties of other molecules. Specifically, molecules of the zwitterion family are mixed in with Fe{H2B(pz)2} 2(bipy). It is found that adding p-benzoquinonemonoimine parent zwitterions locks Fe{H2B(pz)2}2(bipy) to a low spin state so that it persists at room temperature. It may subsequently be unlocked through soft X-ray exposure. It is found that when Fe{H2 B(pz)2}2(bipy) is mixed with other polar molecules of the zwitterion family, each has a unique effect on the spin state. ^ Lastly, the concept of self-assembly is found to be useful for the fabrication of heterojunctions of graphene nanoribbons. First, homogenous self-assembly strategies were investigated and later expanded to construct nanoribbon heterojunctions. It is found that a Cu(111) substrate causes chevron-type graphene nanoribbons to grow in specific crystallographic directions. Adding an additional benzene ring to the precursor will result in the synthesis of an extended chevron nanoribbon. The extended precursors are shown to form nanoribbon heterostructures when mixed with the chevron precursors.^

Subject Area

Nanoscience|Molecular physics

Recommended Citation

Costa, Paulo S, "Supramolecular Self-Assembly for Functional Multicomponent Structures" (2018). ETD collection for University of Nebraska - Lincoln. AAI10792992.
http://digitalcommons.unl.edu/dissertations/AAI10792992

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