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Polarization phenomena in organic nanostructures
This thesis explores the self-assembly and surface interactions of two classes of organic molecules through scanning tunneling microscopy. The primary scientific goal of this thesis is to better understand the electric polarization in surface-supported organic molecules, whether inherent to a molecule or acquired through intermolecular interactions. First, a class of dipolar molecules, the quinonoid zwitterions, are examined on three noble metal surfaces. Two-dimensional islands of hydrogen-bonded molecules, with aligned dipole moments, are formed on Au(111). However, other structures with zero net dipole moment are observed on Ag(111) and Cu(111). Modifying the molecules with longer substituent tails results in the formation of one-dimensional chains irrespective of the surface. Our calculations show that the dipole moment is not the driving factor determining the self-assembly of these molecules. Instead a more complicated picture emerges in which extensive charge transfer with the surface drastically reduces the dipole moment of the molecule by nearly 9 D, so that dipolar energies become small compared to typical chemical bond energies such as hydrogen bonds. Second, the self-assembly of three molecules, croconic acid, rhodizonic acid, and 3-hydroxyphenalenone (3-HPLN) are studied on three noble metal surfaces. These molecules were chosen due to their ferroelectric bulk properties, which arise from switchable hydrogen bonds. On Ag, croconic acid forms two-dimensional hydrogen bonded sheets which are, in theory, capable of proton transfer. While these compounds form hydrogen bonded structures on Ag(111) and Au(111), on the more reactive Cu(111) surface metal-organic frameworks involving surface metal atoms are observed for rhodizonic acid, highlighting the importance of surface chemistry. Additionally, on an insulating buffer layer, CuN, croconic acid forms a densely packed hydrogen bonded structure, which more closely resembles its bulk phase, demonstrating the effect of charge transfer on self-assembly. Additionally, hydrogen bonded co-crystals of 3-HPLN and croconic acid are synthesized on Au(111). Co-crystals of quinonoid zwitterions and croconic acid are also reported. Guided by the surface science studies, related 3D organic co-crystals were grown. Finally, the topic 2D magic organic clusters is presented as a new branch of research. Five new organic magic clusters are described. The research presented in this thesis has relevance to a broad range of applications including data storage devices and molecular electronics.
Organic chemistry|Nanoscience|Molecular physics|Nanotechnology
Kunkel, Donna, "Polarization phenomena in organic nanostructures" (2014). ETD collection for University of Nebraska - Lincoln. AAI3632474.