Past Research Projects
D. Self-assembly of 2D Organic Crystals
In collaboration with Steve Tait, we are investigating the design rules that control the organization of molecules under conditions of dynamic self-assembly when they order on graphite surfaces. We take advantage of molecular design to test how the information encoded into the molecules dictate their packing on the surface. We employ scanning tunneling microscopy (STM) to generate images, e.g., 50 x 50 nm, that often afford sub-molecular resolution to generate 2D crystal structures. Ongoing projects are focussing on the ordering and anion-binding chemistry of aryl-triazole oligomers.
Image courtesy of Kenji Matsuda, University of Kyoto
144. Castillo, H. D.; Yang, J.; Debnath, S.; Dobscha, J. R.; Trainor, C. Q.; Mortensen, R. D.; Raghavachari, K.; Flood, A. H.; Ortoleva, P. J.; Tait, S. L., Solution-Mediated Annealing Pathways are Critical for Supramolecular Ordering of Complex Macrocycles at Surfaces, J. Phys. Chem. C, 2020 124, 6689-6699. DOI
140. Dobscha, J. R.; Castillo, H.; Li, Y.; Fadler, R.; Taylor, R.; Brown, A.; Trainor, C. Q.; Tait, S. L.; Flood, A. H., Sequence-defined Macrocycles for Understanding and Controlling the Build-up of Hierarchical Order in Self-assembled 2D Arrays, J. Am. Chem. Soc. 2019, 141, 17588-17600. DOI
133. Castillo, H., Espinosa-Duran, J. M.; Dobscha, J. R.; Ashley, D. C.; Debnath, S.; Hirsch, B. E.; Schrecke, S. R.; Baik, M.-H.; Ortoleva, P. J.; Raghavachari, K.; Flood, A. H.; Tait, S. L., Amphiphile Self-Assembly Dynamics at the Solution-Solid Interface Reveal Asymmetry in Head/Tail Desorption, Chem. Comm. 2018, 54, 10076-10079. DOI
122. Larsen, K. R.; Bähring, S.; Supur, M.; Nielsen, K. A.; Poulsen, T.; Ohkubo, K.; Marlatt, C. W.; Miyazaki, E.; Takimiya, K.; Flood, A. H.; Fukuzumi, S.; Jeppesen, J. O., Ionic manipulation of charge-transfer and photo-dynamics of [60]fullerene confined in pyrrolo-tetrathiafulvalene cage, Chem. Commun. 2017, 53, 9898-9901. DOI
118. Hirsch, B. E.; McDonald, K. P.; Tait, S. L.; Flood, A. H., Physical and chemical model of ion stability and movement within the dynamic and voltage-gated STM tip-surface tunneling junction. Faraday Trans. 2017, 204, 159-172. DOI
117. Qiao, B.; Hirsch, B. E.; Lee, S.; Pink, M.; Chen, C.-H., Laursen, B. W.; Flood, A. H., Ion-Pair Oligomerization of Chromogenic Triangulenium Cations with Cyanostar-modified Anions That Controls Emission in Hierarchical Materials. J. Am. Chem. Soc. 2017, 139, 6226-6233. DOI
105. Hirsch, B. E.; McDonald, K. P.; Flood, A. H.; Tait, S. L., Living on the Edge: Tuning Supramolecular Interactions to Design Two-dimensional Organic Crystals near the Boundary of Two Stable Structural Phases, J. Chem. Phys. 2015, 142, 101914. DOI
104. Hirsch, B. E.; McDonald, K. P.; Qiao, B.; Tait, S. L.; Flood, A. H., Crystal Switching and Anion Binding in Surface Monolayers Modulated by Electric Fields from Scanning Probes, ACS Nano, 2014, 8, 10858–10869. DOI
100. Hirsch, B. E. Lee, S.; Qiao, B.; Chen, C.-H.; McDonald, K. P.; Tait, S. L.; Flood, A. H., Anion-induced dimerization of 5-fold symmetric cyanostars in 3D crystalline solids and 2D self-assembled crystals, Chem. Commun. 2014, 69, 9827–9830. DOI (From themed collection Scanning Probe Studies of Molecular Systems) Cover Art
C. Phosphate Binding for Clean Water and Food Security
In collaboration Heather Allen to investigate the design rules that control the binding of anions at aqueous interfaces.
150. Neal, J. F.; Saha, A.; Zerkle, M.; Zhao, W.; Rogers, M.; Flood, A. H.; Allen, H. C., Molecular recognition and hydration energy mismatch combine to inform ion binding selectivity at aqueous interfaces, J. Phys. Chem. A 2020, 124, 10171-10180. DOI
146. Grooms, A. J.; Neal, J. F.; Ng, K. C.; Zhao, Z.; Flood, A. H., Allen, H. C., Thermodynamic Signatures of the Origin of Anti-Hofmeister Selectivity for Phosphate at Aqueous Interfaces, J. Phys. Chem. A 2020 124, 5621-5630. DOI
145. Van Craen, D.; Flynn, I. G.; Carta, V.; Flood, A. H., Bimetallic Bis-anion Cascade Complexes of Magnesium in Non-Aqueous Solution, Inorg. Chem. 2020, 59, 5939-5948. DOI
138. Neal, J. F.; Zhao, W.; Grooms, A. J.; Smeltzer, M. A.; Shook, B. M.; Flood, A. H.; Allen H. C., Interfacial Supramolecular Structures of Amphiphilic Receptors Drive Aqueous Phosphate Recognition, J. Am. Chem. Soc. 2019, 141, 7876–7886. DOI
130. Neal, J.; Zhao, W.; Grooms, A.; Flood, A. H.; Allen, H., Arginine-Phosphate Recognition Enhanced in Phospholipid Monolayers at Aqueous Interfaces, J. Phys. Chem. C 2018 122, 26362-26371. DOI
124. Gibb, B. C.; Flood, A. H.; Cremer P. S.; Mobley, D. L., “Collaborative Routes to Clarifying the Murky Waters of Aqueous Supramolecular Chemistry” Nat. Chem. 2018, 10, 8-16. DOI
B. Active Plasmonics
Active molecular plasmonics involves the manipulation of light at the nanoscale using functional chromophores. Presently, large progress has been made in generating reproducible nanopatterns with tunable plasmons. The opportunity now emerges to interface functional molecules to these surfaces that have the potential information processing and sensing. However, fundamental questions remain such as how to tune molecular chromophores to couple the plasmons of patterned surfaces. This research program harnesses synthesis, spectroscopy and theory to address this question using colored host-guest complexes as the functional units. Here at IU, we make use of surface-enhanced resonance Raman scattering (SERRS) spectroscopy to quantify the coupling between plasmon and chromophore. Insight gained from these studies will also allow for quantitative studies of the numbers and identities of molecules on surfaces – laying the foundation for sensing.
123. Witlicki, E. H. Bähring, S.; Johnson, C.; Solano, M. V.; Nielsen, K. A.; Silverstein, D. W.; Marlatt, C. W.; Jensen, L.; Jeppesen, J. O.; Flood, A. H.; Enhanced detection of explosives by turn-on resonance Raman upon host-guest complexation in solution and solid state, Chem. Commun. 2017, 53, 10918-10921. DOI
75 Witlicki, E. H.; Johnsen, C.; Hansen, S. W.; Silverstein, D. W.; Bottomley, V. J.; Jeppesen, J. O.; Wong, E. W.; Jensen, L.; Flood, A. H.* Molecular Logic Gates Using Surface-Enhanced Raman-Scattered Light, J. Am. Chem. Soc.. 2011, 133, 7288–7291. DOI
70 Witlicki, E. H.; Andersen, S. S.; Hansen, S. W.; Jeppesen, J. O.; Wong, E. W.; Jensen, L. Flood, A. H., Turning on resonant SERRS using the chromophore-plasmon coupling created by host-guest complexation at a plasmonic nanoarray, J. Am. Chem. Soc. 2010, 132, 6099-6107. DOI
61 Witlicki, E. H.; Hansen, S.; Christensen, M.; Hansen, T.; Nygaard, S.; Jeppesen, J. O.; Wong, E. W.; Jensen, L.; Flood, A. H., Determination of binding strengths of a host-guest complex using resonance Raman scattering, J. Phys. Chem. A 2009, 113, 9450-9457. DOI
A. Redox Active Molecular Wires from Mixed-Valency (2005–2007)
This research addresses the needs of the microelectronics community to extend Moore's Law.
Mixed-valent (MV) coordination compounds (Figure 1) that have delocalized systems will be targeted. Such molecules are attractive systems to transfer from solution to devices in a systematic manner based on (1) structure-property relationships and (2) structurally-sensitive spectroscopy. One component of this research relies upon the development of synthetic methods to functionalize ligands with thiol-based "alligator clips". Secondly, solution-phase Raman spectra will be used to show how the molecular wires behave under bias (+/–) employing self-assembled monolayers (SAMs) as stepping-stones to devices. Their electronic and spectroscopic behavior will be characterized in half devices.
This project was funded by the NSF NER program.
• Whence Molecular Electronics? (178 citations)
Flood, A. H.; Stoddart, J. F.; Steuerman, D. W.; Heath, J. R., Science 2004, 306, 2055-2056.