(65ar) Infrared Spectroscopic Characterization of Bifunctional Organic Linker Molecules

The overall focus of this project is the self-assembly of three-dimensional ?colloidal? molecules using micrometer and submicrometer-sized particles. The assembly of particles is controlled by (i) the modification of particle surfaces with reactive patches, creating so-called patchy particles, and (ii) the use of organic bifunctional linkers to connect the colloidal building blocks. In the project presented here, we are exploring molecules that may be used as bifunctional linkers between patchy particles. These linker molecules have functional groups that are reactive towards a specific patch material on the particles. In order to determine whether the linker molecules have successfully reacted with the patches, their presence must be detected. The most convenient way to characterize the molecules is infrared (IR) spectroscopy, which is very sensitive towards the functional groups available in the molecules. In order to understand what change the molecules undergo during reaction, a comprehensive analysis of the linker molecules with IR absorption spectroscopy is needed. To this end, we measured the IR spectra of the free molecules in an appropriate IR set up. The molecules characterized with IR in this report are: 1,8-octanedithiol, 1,8-diaminooctane, 1,8-octanediol, and 1,8-octanedioic acid. Using the best spectra collected, peaks are analyzed to determine peak position and interpreted using available literature values. More importantly, peaks that are unique to each linker and functional group are identified. Two of these linker molecules, 1,8-octanedithiol, and 1,8-diaminooctane, are then reacted with gold surfaces, to form self-assembled monolayers. Subsequently, the IR spectra of these surfaces, using Diffuse Reflectance setup, are taken and compared to the spectra of the free molecules in solution. We find that the bifunctional molecules form organized monolayers using the difunctional molecules. For the monofuntional molecules, 1-Octanethiol and 1-Octylamine, the spectra are weak indicating a disorganized monolayer formation.