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This thesis presents evidence of preferential adsorption and the associated dipole-dipole interactions that can occur at molecule to molecule interfaces. The results are discussed in the context of the possibility of interactions caused by strong intrinsic dipoles when adsorbed on electrostatically biased substrates. Key is the discovery of lock and key adsorption chemistry by comparing the reversible absorption of the three isomers of di-iodobenzene (1,2-di-iodobenzene, 1,3-di-iodobenzene, and 1,4-di-iodobenzene) on molecular films of a quinonoid zwitterion. There is unequivocal evidence that the molecular adsorption and absorption of 1, 3-diiodobenzene is strongly favored at 150 K over the other isomers of di-iodobenzene. Our experiments also demonstrate that reversible isomer-selective adsorption chemistry of small molecules is indeed possible, with a preferential adsorption mechanism illustrating that symmetry does matter.
Evidence of selective adsorption on specific ferroelectric domains of the molecular ferroelectric, copolymers of polyvinylidene fluoride with trifluoroethylene (PVDF-TrFE) is presented. The adsorption of di-iodobenzene depends not only on the dipole orientation of the PVDF-TrFE ferroelectric domains, but also the di-iodobenzene isomer.
Foundational to this work is the investigation of the interaction and orientation of a strongly dipolar zwitterionic p-benzoquinonemonoimine-type molecule, with a large intrinsic dipole of 10 Debye, on both conducting (gold) and on polar insulating substrates (lithium niobate). I have studied surface electronic spectroscopic properties and the preferential absorption pattern of these unusual zwitterionic molecules C6H2(···NHR)2(···O)2, where R = H, n-C4H9, C3H6-S-CH3, C3H6-O-CH3, CH2-C6H5 on gold and demonstrated the selective deposition of molecules onto specific ferroelectric domains for a spatially periodically poled ferroelectric surface (lithium niobate).
Advisor: Peter A. Dowben