Date of Award

2013

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Chemistry and Biochemistry

First Advisor

T. Carmichael

Keywords

Pure sciences, Applied sciences, Chelation, Dithiophosphinic acids, Interfacial properties, Self-assembled monolayers, Surface chemistry, van der Waals interactions

Rights

CC BY-NC-ND 4.0

Abstract

This dissertation reports the synthesis of derivatives of dithiophosphinic acids (R 1 R 2 DTPAs), and the formation and characterization of DTPA SAMs on gold to build a knowledge base on their nature of binding, organization of the alkyl chains and electrochemical barrier properties. The binding of DTPA molecules on gold depends on the morphology of the gold film: They bind in a mixed monodentate and bidentate modes on standard as-deposited (As-Dep) gold, while they fully chelate on smoother template-stripped (TS) gold. Chapter 2 focuses on van der Waals interactions of various alkyl chain lengths of symmetrical R 2 DTPA SAMs, which increase with increasing chain lengths similar to those of the analogous n -alkanethiol SAMs, but with alkyl chains that are generally less dense than those of n -alkanethiol SAMs. Chapter 3 addresses why the DTPA compounds do not chelate on the standard As-Dep gold by comparing (C 16 ) 2 DTPA SAM to (C 16 ) 2 DDP SAM. Here, side chain crystallinity stabilizes DTPA SAM structure at the expense of chelation of the DTPA molecules, which leads to a mixture of bidentate and monodentate DTPA molecules, whereas the increased flexibility of the chains in DDP due to the oxygen atoms retains chelation of the DDP molecules. Chapter 4 focuses on the SAMs formed from Rl ong R short DTPAs, which shows that the length of the short chain spacer affects SAM packing density and thickness. The SAMs of these molecules also show homogeneous mixing of R long and R short chains. Chapter 5 investigates PhRDTPA SAMs in preparation for molecular junction studies. The chelation of PhRDTPA molecules on TS gold allows the PhRDTPAs to act as molecular alligator clips. The length of the alkyl chains controls the density of the phenyl group and they fill in the voids between adsorbates to prevent electrical shorting. Finally, Chapter 6 incorporates OH tail group(s) to control the wettability of DTPA SAMs. The presence of OH groups in DTPAs forms hydrophilic SAMs. The symmetrical OH-terminated DTPA forms a SAM with similar packing density to that of an analogous CH 3 -terminated DTPA SAM, while the OH/CH 3 -terminated DTPA forms a thin SAM with low molecular packing, however, the chains of this SAM are homogeneously mixed.

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