Indiana University Department of Chemistry Indiana University Department of Chemistry - Amar Flood Research Group Indiana University Department of Chemistry - Amar Flood Research Group Indiana university Bloomington
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Research

Relevant Disciplines

Physical Organic / Inorganic / Materials

Related Areas

Nanoscience - Spectroscopy and Electrochemistry - Supramolecular Chemistry - Interfacial Science

 

1. Anion Recognition with Triazolophanes

(Relevant Publications)

We have developed a novel shape-persistent macrocycle (see image below) that is easily constructed using click chemistry and displays a high affinity for anions. This is one of the first three examples of the weak CH•••anion hydrogen bond (the weakest among Nature's cohort) to be reported and therefore represents an iconoclastic breakthrough in the design of anion receptors. Consequently, the extreme modularity provided by the click chemistry as well as the high affinity (some approaching Ka values of 1,000,000 M–1) open up a new and uncharted realm of opportunities. Our goals are to sequester toxic anions from the environment, deliver them to safe locations and, by using our knowledge of molecular machines, to release them int captivity using a photo-driven light switch.

Funding:

NSF-CAREER Award (CHE-0844441)

DOE-BES

 

2. Molecular Switches and Non-Innocent Ligands

(Relevent Publications)

We have developed redox-active ligands that can serve as switches to the investigation of mechanical motion at the molecular level. Attention is focused on the Cu(I) as a labile transition metal coupled with non-innocent bridging ligands. The thermodynamics and kinetics of the switching will be quantified. We intend to broaden the diversity of ligand-based switching to other metals and extend the complexity of what can be achieved using catenates and rotaxanes that can perform a range of functions -- such as molecular muscles.

 

3. Active Molecular Plasmonics utilizing Molecular Recognition

(Relevent Publications)

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.

 

 

4. Redox Active Molecular Wires from Mixed-Valency

(Relevent Publications)

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 is funded by the NSF NER program.

 

 

 

Relevant Publications

  1. ANION RECOGNITION:
    •Triazolophanes: A new class of halide-selective ionophores for potentiometric sensors
    Zahran, E.; Hua, Y.; Li, Y.; Flood, A. H.; Bachas , L. G., Anal. Chem. 2009, in press.
    •Strong CH•••halide hydrogen bonds from 1,2,3-triazoles quantified using pre-organized and shape-persistent triazolophanes
    Bandyopadhyay, I.; Raghavachari, K.; Flood, A. H., ChemPhysChem. 2009, 10, 2535-2540. DOI
    • Dipole-Promoted and Size-Dependent Cooperativity between Pyridyl-Containing Triazolophanes and Halides Leads to Persistent Sandwich Complexes with Iodide
    Li, Y.; Pink, M.; Karty, J. A.; Flood, A. H., J. Am. Chem. Soc. 2008, 130, 17293-17295. DOI
    • Strong, size-selective, and electronically-tunable C–H•••halide binding with steric control over aggregation from synthetically modular, shape-persistent [34]triazolophanes
    Li, Y.; Flood, A. H., J. Am. Chem. Soc. 2008, 130, 12111-12122. DOI
    • Pure CH hydrogen bonding to chloride ions: A pre-organized and rigid macrocyclic receptor
    Li, Y.; Flood, A. H., Angew. Chem. Int. Ed. 2008, 47, 2649-2652. DOI
    32 Citations garnered to date (Nov 2009)
    See also the news coverage by: (Chem. & Eng. News, Nature Chemistry World)
  2. MOLECULAR SWITCHES:
    • Pinpointing the extent of electronic delocalization in the Re(I)-to-tetrazine charge-separated excited state using time-resolved infrared spectroscopy
    Li, G.; Parimal, K.; Vyas, S.; Hadad, C. M.; Flood, A. H.; Glusac, K. D., J. Am. Chem. Soc. 2009, 131, 11656-11657. DOI.
    •     Reduction of a redox-active ligand drives switching in a Cu(I) pseudorotaxane by a bimolecular mechanism
    McNitt, K. A.; Parimal, K.; Share, A. I.; Fahrenbach, A. C.; Witlicki, E. H.; Pink, M.; Bediako, D. K.; Plaisier, C. L.; Le, N.; Heeringa, L. P.; Vander Griend, D. A.; Flood, A. H., J. Am. Chem. Soc. 2009, 131, 1305-1313. DOI
    • Can Terdentate 2,6-Bis(1,2,3-Triazol-4-yl)Pyridines form Stable Coordination Compounds?
    Li, Y.; Huffman, J. C.; Flood, A. H. Chem. Commun. 2007, 2692-2694. DOI
    27 Citations garnered to date (Nov 2009)
    • Linear Artificial Molecular Muscles (179 citations)
    Liu, Y., Flood, A. H. Bonvallet, P. A.; Vignon A. S.; Northrup, B.; Tseng. H.-R.; Jeppesen, J. O.; Huang, T. J.; Brough, B.; Baller, M.; Magonov, S.; Solares, S.; Goddard, W. A.; Ho, C.-M.; Stoddart, J. F., J. Am. Chem. Soc. 2005, 127, 9745–9759;
    • Meccano on the Nanoscale - A Blueprint for making Some of the World's Tiniest Machines (133 citations)
    Flood, A. H.; Ramirez, R. J. A.; Deng, W.-Q.; Muller, R. P.; Goddard, W. A.; Stoddart, J. F., Aust. J. Chem. 2004, 57, 301-322.
  3. ACTIVE MOLECULAR PLASMONICS:
    •Determination of binding strengths of a host-guest complex using resonance Raman scattering
    Witlicki, E. H.; Hansen, S.; Christensen, M.; Hansen, T.; Nygaard, S.; Jeppesen, J. O.; Wong, E. W.; Jensen, L.; Flood, A. H., J. Phys. Chem. A 2009, 113, 9450-9457. DOI
    • Active Molecular Plasmonics: Controlling Plasmon Resonances with Molecular Switches
     Zheng, Y. B.; Yang, Y-W.; Jensen, L.; Fang, L.; Juluri, B. K.; Flood, A. H.; Weiss, P. S.; Stoddart, J. F.; Huang, T. J., , Nano Lett. 2009, 9, 819-825. DOI
    • Revealing the Chromophoric Composition of Multichromophoric Polypyridyl Complexes of Re(I) and Os(II): A Resonance Raman Study
    Flood, A.; Girling, R.; Hester, R.; Moore, J.; Gordon, K. C.; Polson, M. I. J., J. Raman Spectrosc. 2002, 33, 434-442.
  4. MOLECULAR ELECTRONICS:
    • Whence Molecular Electronics? (163 citations)
    Flood, A. H.; Stoddart, J. F.; Steuerman, D. W.; Heath, J. R., Science 2004, 306, 2055-2056.