AVS 65th International Symposium & Exhibition
    Processing and Characterization of Air-Liquid, Solid-Liquid and Air-Solid Interfaces Focus Topic Tuesday Sessions
       Session PC+AS+BI+EM+NS+PB+SS-TuA

Paper PC+AS+BI+EM+NS+PB+SS-TuA12
Polymorphism of Hydrogen-Bonded Clusters at the Vacuum-Solid Interface

Tuesday, October 23, 2018, 6:00 pm, Room 202A

Session: Progress in Industrial Processes and Characterization of Interfaces and Gas-Solid Interfacial Processes and Characterization
Presenter: Angela Silski, University of Notre Dame
Authors: A. Silski, University of Notre Dame
J. Petersen, University of Notre Dame
R.D. Brown, Clarkson University
S. Corcelli, University of Notre Dame
S.A. Kandel, University of Notre Dame
Correspondent: Click to Email
Molecular self-assembly is an attractive bottom-up approach to nanostructure fabrication. Using molecules as building blocks and carefully tuning the non-covalent intermolecular interactions, unique nanostructured architectures can be designed. Given the structure/function relationship on the nano- and meso-scale, this bottom-up approach to designing new architectures is critical in the careful design of novel materials with desired chemical properties. In this study, the role of hydrogen bond donor/acceptor position in metastable cluster formation is explored using scanning tunneling microscopy (STM) with complementary density functional theory (DFT) calculations. We observe a metastable cyclic pentamer for isatin (1H-indole-2,3-dione) with DFT providing support for a cyclic structure stabilized by both NH...O and CH...O hydrogen bonds between neighboring molecules. The CH...O hydrogen bond is made between the 7-position proton acting as the hydrogen bond donor and the 3-position carbonyl as the hydrogen bond acceptor, and calculations indicate that the isatin pentamer structure is 12 kJ/mol more stable than the dimer on the per molecule basis. To probe the importance of the CH...O hydrogen bond in stabilizing the isatin pentamer, we compare to isatin derivatives: we replace the 3-position carbonyl with a methyl group (3-methyl 2-oxindole), the 7-position proton with a fluorine (7-fluoroisatin), systematically move the location of the hydrogen bond donor/acceptor by one position, (phthalimide), and remove of the primary hydrogen bond donor (1,2-indandione and 1,3-indandione). We show that cyclic pentamer formation is either altered or precluded as a result of these substitutions. Additionally, the importance of CH...O bonding in forming isatin pentamers is supported by electrospray ionization mass spectrometry (ESI-MS) measurements, which include a magic-number isatin pentamer peak, whereas the derivative molecules show little clustering under the same conditions. This work is significant in understanding the role that the position of the hydrogen bond donor/acceptor groups has on the resulting 2D supramolecular assemblies.