Research
Relevant Disciplines: Organic / Inorganic / Materials / Supramolecular
1. Anion Recognition
We have four main motifs: triazolophane macrocycles, aryl-triazole cages, aryl-triazole foldamers, and cyanostar macrocycles
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 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 in dichloromethane) open up a new and uncharted realm of opportunities. One of our goals are to sequester toxic anions from aqueous environment, deliver them to safe locations and, by using our knowledge of molecular machines, to release them into captivity using a photo-driven light switch – which is where we were able to highlight our use of aryl-triazole foldamers.
New goals include the chelation, sensing, regulation, and transport of chloride and phosphate in biological mileu.
We have leveraged our understanding of receptor design and CH based hydrogen bonding to create a wholly new class of macrocyclic receptors, called cyanostars. We made a couple of exciting discoveries during our initial studies, as outlined in the Nature Chemistry article. First, the macrocycles can be made in one pot with high yields (>80%) and on 10-g scales. Second, we were able to bind anions like PF6 that were originally thought to be non-coordinating and then, after re-evaluation in the 1970's to be "weakly coordinating" – perhaps that idea needs to be completely reformulated because of the extremely high affinities observed with cyanostars showing logK ~ 12. Third, we created a new class of anion-templated rotaxanes using dialkylphosphates. All of these discoveries represent areas for deeper understanding and further exploration.
158. Parks, F. C.; Sheetz, E. G.; Stutsman, S. R.; Lutolli, A.; Debnath, S.; Raghavachari, K.; Flood, A. H., Revealing the hidden costs of organization in host-guest chemistry using chloride-binding foldamers and their solvent dependence. J. Am. Chem. Soc. 2022, 144, 1274-1287. DOI
157. Lutolli, A.; Flood, A. H., Photoswitchable Ion Receptors, Book Chapter for “Molecular Photoswitches – Synthesis, Properties and Applications,” Ed. Z. Pianowski, Wiley 2022 DOI
156 Sheetz, E. G.; Van Craen, D.; Flood, A. H., Anion recognition and binding constant determination, Book Chapter for “Anion Assisted Catalysis,” Ed. O. Garcia Mancheno, Wiley 2021 DOI
151. Liu, Y.; Parks, F. C.; Sheetz, E. G.; Chen, C.-H.; Flood, A. H. Polarity-Tolerant Chloride Binding in Foldamer Capsules by Programmed Solvent-Exclusion, J. Am. Chem. Soc. 2021, 143, 3191-3204. DOI
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
139. Liu, Y.; Zhao, W.; Chen, C.-H.; Flood, A. H., Chloride capture using a C–H hydrogen bonding cage, Science. 2019, 365, 159-161. (Nominated for Molecule of the Year by Chemical and Engineering News) DOI
135. Parks, F. C.; Liu, Y.; Stutsman, S. R.; Debnath, S.; Raghavachari, K.; Flood, A. H., “Allosteric Control of Photofoldamers for Selecting between Anion Regulation and Double-to-Single Helix Switching, J. Am. Chem. Soc. 2018, 140, 17711-17723. DOI
134. Liu, Y.; Parks, F. C.; Zhao, W.; Flood, A. H., “Sequence-controlled Stimuli-responsive Single-Double Helix Conversion between 1:1 and 2:2 Chloride-Foldamer Complexes” J. Am. Chem. Soc., 2018, 140, 15477-15486. DOI
132. Sengupta, A.; Liu, Y.; Flood, A. H., Raghavachari, Anion-binding Macrocycles Operate Beyond the Electrostatic Regime: Interaction Distances Matter, Chem. Eur. J. 2018, 24, 14409-14417. DOI
127. Dobscha, J. R.; Debnath, S.; Fadler, R. E.; Fatila, E. M.; Pink, M.; Raghavachari, K.; Flood, A. H., Host-host Interactions Control Self-assembly and Switching of Triple and Double Decker Stacks of Tricarbazole Macrocycles Co-assembled with Anti-electrostatic Bisulfate Dimers, Chem. Eur. J. 2018, 24, 9841-9852. 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
120. Liu, Y.; Sengupta, A.; Raghavachari, K.; Flood, A. H., Anion binding in solution: Beyond the electrostatic regime, Chem. 2017, 3, 411-427 DOI
116. Dobscha, J. R.; Liu, Y.; Flood, A. H., Shape-persistent Anion Receptors. In Comprehensive Supramolecular Chemistry II; Elsevier, 2016
110. Flood, A. H., Creating molecular macrocycles for anion recognition, Beilstein J. Org. Chem. 2016, 12, 611-627. DOI
108. Lee, S.; Hirsch, B. E.; Liu, Y.; Dobscha, J. R.; Burke, D. W.; Tait, S. L.; Flood, A. H., Multifunctional Tricarbazolo Triazolophane Macrocycles: One-Pot Preparation, Anion Binding, and Hierarchical Self-Organization of Multilayers, Chem. Eur. J. 2016, 22, 560–569. Cover Art DOI
107. Qiao, B.; Sengupta, A.; Liu, Y.; McDonald, K. P.; Pink, M.; Anderson, J.; Raghavachari, K.; Flood, A. H., Electrostatic and Allosteric Cooperativity in Ion-pair Binding: A Quantitative and Coupled Experiment-Theory Study with Aryl-Triazole-Ether Macrocycles, J. Am. Chem. Soc. 2015, 137, 9746-9757. 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
103. Liu, Y.; Flood, A. H., Ch. 9: Synergistic Effects in Double Helical Foldamers, Synergy in Supramolecular Chemistry, Ed. Tatsuya Nabeshima, CRC Press, 2014. (Link 1)
102. McDonald, K. P.; Qiao, B.; Twum, E. B.; Lee, S.; Gamache, P. J.; Chen, C.-H.; Yi, Y.; Flood, A. H., Chloride-binding poly(methyl methacrylate) copolymers bearing aryl-triazole side chains induce changes in polymer size and enhance salt extraction, Chem. Commun., 69, DOI
101. Lee, S.; Hua, Y.; Flood, A. H., Beta Sheet-Like Hydrogen Bonds Interlock the Helical Turns of a Photoswitchable Foldamer to Enhance the Binding and Release of Chloride, J. Org. Chem. 2014, 79. DOI
99. Chen, T.-H.; Lee, S.; Flood, A. H.; Miljanic, O. S., How to print a crystal structure model in 3D, CrystEngComm 2014, 16, 5488–5493. OPEN ACCESS–DOI Cover Art
97. Ramabhadran, R. O.; Liu, Y.; Hua, Y.; Ciardi, M.; Flood, A. H.; Raghavachari, K., An Overlooked yet Ubiquitous Fluoride Congenitor: Binding Bifluoride in Triazolophanes using Computer-Aided Design, J. Am. Chem. Soc. 2014, 136, 5078–5089. DOI
96. Ramabhadran, R. O.; Hua, Y.; Flood, A. H.; Raghavachari, K., C vs N: Which End of the Cyanide Anion is a Better Hydrogen Bond Acceptor?, J. Phys. Chem. 2014,118, 7418–7423. DOI
93. Hua, Y; Liu, Y; Chen, C.-H.; Flood, A. H., Hydrophobic Collapse of Foldamer Capsules Drives Picomolar-Level Chloride Binding in Aqueous Acetonitrile Solutions, J. Am. Chem. Soc. 2013, 135, 14401–14412. DOI
90. Lee, S.; Flood, A. H., Photoresponsive receptors for binding and releasing anions (Mini Review), J. Phys. Org. Chem. 2013 26, 79-86. Cover Art DOI
83 Lee, S.; Flood, A. H., Binding anions in rigid and reconfigurable triazole receptors, Topics Het. Chem. 2012, 28, 85-107. DOI
82 McDonald, K. P.; Hua, Y.; Lee, S.; Flood, A. H., Shape Persistence Delivers Lock-and-Key Chloride Binding in Triazolophanes, Chem. Commun. 2012, 48, 5065-5075. Cover Art DOI
81 Flood, A. H., Profile: Early Excellence in Physical Organic Chemistry J. Phys. Org. Chem. 2011 DOI
80 McDonald, K. P.; Ramabhadran, R. O.; Lee, S.; Raghavachari, K., Flood, A. H., Polarized Naphthalimide CH Donors Enhance Cl Binding Within an Aryl-Triazole Receptor, Org. Lett. 2011, 13, 6260-6263. DOI
78 Ramabhadran, R. O.; Hua, Y.; Flood, A. H.; Raghavachari, K., From Atomic to Molecular Anions: A Neutral Receptor Captures Cyanide using Strong C–H Hydrogen Bonds, Chem. Eur. J. 2011, 17, 9123-9129. DOI
75 Hua, Y.; Ramabhadran, R. O.; Karty, J. A.; Raghavachari, K.; Flood, A. H., Two levels of conformational pre-organization consolidate strong CH hydrogen bonds in chloride-triazolophane complexes, Chem. Commun. 2011, 47, 5979-5981. DOI
74 Zahran, E. M.; Hua, Y.; Lee, S.; Flood, A. H.; Bachas, L. G., Ion-selective electrodes based on a pyridyl-containing triazolophane: Manipulating halide selectivity by mixing dipole-promoted cooperativity with hydrogen bonding, Anal. Chem. 2011, 83, 3455-3461. DOI
73 Hua, Y.; Ramabhadran, R. O.; Uduehi, E. O.; Karty, J. A.; Raghavachari, K.; Flood, A. H., Aromatic and aliphatic CH hydrogen bonds fight for chloride while competing alongside ion pairing within triazolophanes, Chem. Eur. J. 2011, 17, 312-321. DOI.
72 Hua, Y.; Flood, A. H., Flipping the switch on chloride concentrations with a light-active foldamer, J. Am. Chem. Soc. 2010, 132, 12838-12840. DOI.
70 Lee, S.; Hua, Y. Park, H.; Flood, A. H., Intramolecular hydrogen bonds preorganize aryl-triazole receptor into a crescent for chloride binding, Org. Lett. 2010, 12, 2100-2101. DOI
66 Hua, Y.; Flood, A. H., Click chemistry generates priviliged CH hydrogen-bonding triazoles: the latest addition to anion supramolecular chemistry, Chem. Soc. Rev. 2010, 39, 1262-1271. DOI
65 McDonald, K. P.; Hua, Y.; Flood, A. H., 1,2,3-Triazoles and the Expanding Utility of Charge Neutral CH•••Anion Interactions, Anion Receptors Special Issue in Topic in Heterocyclic Chemistry, Springer, 2010. DOI
63 Zahran, E.; Hua, Y.; Li, Y.; Flood, A. H.; Bachas , L. G., Triazolophanes: A new class of halide-selective ionophores for potentiometric sensors, Anal. Chem. 2010, 82, 368-375. DOI
60 Bandyopadhyay, I.; Raghavachari, K.; Flood, A. H., Strong CH•••halide hydrogen bonds from 1,2,3-triazoles quantified using pre-organized and shape-persistent triazolophanes, ChemPhysChem. 2009, 10, 2535-2540. DOI
59 Li, Y.; Vander Griend, D. A.; Flood, A. H., Modelling triazolophane-halide binding equilibria using Sivvu analysis of UV-vis titration data recorded under medium binding conditions, Supramolec. Chem. 2009, 21, 111-117. (Special Issue for the III International Symposium on Macrocyclic and Supramolecular Chemistry, Las Vegas 2008), DOI
55 Li, Y.; Pink, M.; Karty, J. A.; Flood, A. H., Dipole-Promoted and Size-Dependent Cooperativity between Pyridyl-Containing Triazolophanes and Halides Leads to Persistent Sandwich Complexes with Iodide, J. Am. Chem. Soc., 2008, 130, 17293-17295. DOI
53 Li, Y.; Flood, A. H., “Strong, size-selective, and electronically-tunable C–H•••halide binding with steric control over aggregation from synthetically modular, shape-persistent [34]triazolophanes, J. Am. Chem. Soc. 2008, 130, 12111-12122. DOI
52 Li, Y.; Flood, A. H., "Pure CH hydrogen bonding to chloride ions: A pre-organized and rigid macrocyclic receptor," Angew. Chem. Int. Ed. 2008, 47, 2649-2652. DOI
See also the news coverage by: Chem. & Eng. News, • Nature • Chemistry World
166. Dhara, A.; Fadler, R. E.; Chen, Y.; Kottner, L. A.; Van Craen, D.; Carta, V.; Flood, A. H., Orthogonal, modular anion-cation and cation-anion self-assembly using pre-programmed anion binding sites, Chem. Sci. 2023, 14, 2585-2595. DOI
164. Sheetz, E. G., Marogil, A.; Che, M.; Pink, M.; Carta, V.; Raghavachari, K.; Flood, A. H. High-fidelity Recognition of Organotrifluoroborate Anions (R–BF3–) as Designer Guest Molecules. Chem. Eur. J. 2022, 28, e202201584. DOI
162. Li, Y.; Saha, A.; Zhao, W.; Neil, J. F.; Chen, Y.; Flood, A. H.; Allen, H. C., Recognition competes with hydration in anion-triggered monolayer formation of cyanostar supra-amphiphiles at aqueous interfaces. Chem. Sci. 2022, 13, 4283-4294. DOI
161. Fadler, R. E.; Flood, A. H., Rigidity and Flexibility in Rotaxanes and Their Relatives On being Stubborn and Easy Going, Frontiers in Chemistry, Special Issue on Advances in Mechanically Bonded Molecules. Front. Chem. 2022, 10, #856173 DOI
160. Benasco, A. R.; Tropp, J.; Kaphle, V.; Chen, Y.; Zhao, W.; Eedugurala, N.; Ng, T. N.; Flood, A. H.; Azoulay, J. D. Receptor Induced Doping of Conjugated Polymer Transistors: A Strategy for Selective and Ultrasensitive Phosphate Detection in Complex Aqueous Environments, Adv. Elect. Mat. 2022, 8, #2101353. DOI
154. Zeynaloo, E.; Zahran, E. M.; Fatila, E. M.; Flood, A. H.; Bachas, L. G., Anion-selective electrode based on a CH-hydrogen bonding bis-macrocyclic ionophore with a clamshell architecture, Anal. Chem. 2021, 93, 5412. DOI
152. Fadler, R. E.; Al Ouahabi, A.; Qiao, B.; Carta, V.; König, N. F.; Gao, X.; Zhao, W.; Zhang, Y.; Lutz, J.-F.; Flood, A. H., Chain Entropy Beats Hydrogen Bonds to Unfold and Thread Dialcohol Phosphates inside Cyanostar Macrocycles to form [3]Pseudorotaxanes. J. Org. Chem. 2021, 86. DOI
148. White, N.; Zhao, W.; Flood, A. H., Recognition and Applications of Anion–Anion Dimers based on Anti-Electrostatic Hydrogen Bonds (AEHBs), Chem. Soc. Rev. 2020, 49, 7893-7906. DOI
147. Dhara, A.; Sadhukhan, T.; Sheetz, E. G.; Raghavachari, K.; Flood A. H., Zero-overlap Fluorophores for Fluorescent Studies at Any Concentration, J. Am. Chem. Soc. 2020 142, 12167-12180. DOI
142. Zhao, W.; Tropp, J.; Qiao, B.; Pink, M.; Azoulay, J. D.; Flood, A. H., Tunable Adhesion from Stoichiometry-controlled and Sequence-defined Supramolecular Polymers Emerges Hierarchically from Cyanostar-stabilized Anion-anion Attractions, J. Am. Chem. Soc., 2020. 142, 2579–2591. DOI
137. Zhao, W.; Qiao, B.; Tropp, J.; Pink, M.; Azoulay, J.; Flood, A. H., Linear Supramolecular Polymers Driven by Anion-Anion Dimerization of Difunctional Phosphonate Monomers inside Cyanostar Macrocycles, J. Am. Chem. Soc. 2019, 141, 4980-4989. DOI
131. Qiao, B.; Leverick, G.; Zhao, W.; Flood, A. H.; Johnson, J; Shao-Horn, Y., Supramolecular Regulation of Anions Enhances Conductivity and Transference Number of Lithium in Liquid Electrolytes, J. Am. Chem. Soc. 2018 140, 10932–10936. DOI
129. Sheetz, E. G.; Qiao, B.; Pink, M.; Flood, A. H., Programmed Negative Allostery with Guest-selected Rotamers Control Anion-anion Complexes of Stackable Macrocycles, J. Am. Chem. Soc., 2018, 7773-7777. DOI
128. Benson, C. R.; Maffeo, C.; Fatila, E. M.; Liu, Y.; Sheetz, E. G.; Aksimentiev, A.; Singharoy, A.; Flood, A. H., “Inchworm movement of two rings switching onto a thread by biased Brownian diffusion: a three-body problem” Proc. Natl. Acad. Sci. USA 2018,38, 9391-9396. DOI
126. Fatila, E. M.; Pink, M.; Twum, E. B.; Karty, J. A.; Flood, A. H., Phosphate-phosphate oligomerization drives higher order co-assemblies with stacks of cyanostar macrocycles, Chem. Sci. 2018, 9, accepted Cover Art. DOI
125. Zahran, E. M.; Fatila, E. M.; Chen, C.-H, Flood, A. H.; Bachas, L. G., Cyanostar: C–H Hydrogen Bonding Neutral Carrier Scaffold for Anion-Selective Sensors, Anal. Chem. 2018, 90, 1925-1933. DOI
121. Zhao, W.; Qiao, B.; Chen, C.-H., Flood, A. H., High Fidelity Multi-state Switching with Anion-Anion and Acid-Anion Dimers of Organophosphates in Cyanostar Complexes, Angew. Chem. Int. Ed. 2017, 56, 13083-13087 DOI
119. Fatila, E. M.; Twum, E. B.; Karty, J. A.; Flood, A. H., Ion-pairing and Co-facial Stacking Drive High-fidelity Bisulfate Assembly with Cyanostar Macrocyclic Hosts, Chem. Eur. J. 2017, 23, Early View 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
116. Dobscha, J. R.; Liu, Y.; Flood, A. H., Shape-persistent Anion Receptors. In Comprehensive Supramolecular Chemistry II; Elsevier, 2016
115. Qiao, B.; Liu, Y.; Lee, S.; Pink, M.; Flood, A. H., High-yield Synthesis and Acid-base Response of Phosphate-templated [3]Rotaxanes, Chem. Commun. 2016, 52, 13675-13678. DOI
114. Benson, C. R.; Fatila, E. M.; Lee, S.; Marzo, M. G.; Pink, M.; Mills, M. B.; Preuss, K. E.; Flood, A. H., Extreme Stabilization and Redox Switching of Organic Anions and Radical Anions by Large-cavity, CH Hydrogen-Bonding Cyanostar Macrocycles, J. Am. Chem. Soc. 2016, 138, 15057-15065. DOI (See highlight in Cutting Edge Chemistry from the ACS)
113. Fatila, E. M.;Twum, E. B.; Sengupta, A.; Pink, M.; Karty, J. A.; Raghavachari, K.; Flood, A. H., Anions Stabilize Each Other inside Macrocyclic Hosts, Angew. Chem. Int. Ed. 2016, 55, 14057-14062. DOI (See highlghts in C&EN, Quartz, Spectroscopy Now, NSF, and IU Press Release, as well as in the popular press).
112. Qiao, B.; Anderson, J. R.; Pink, P.; Flood, A. H., Size-matched Recognition of Large Anions by Cyanostar Macrocycles is Saved when Solvent-bias is Avoided, Chem. Comm. 2016, 52, accepted. DOI
111. Liu, Y.; Singharoy, A.; Mayne, C. G.; Sengupta, A.; Raghavachari, K.; Shulten, K.; Flood, A. H., Flexibility Coexists with Shape-Persistence in Cyanostar Macrocycles, J. Am. Chem. Soc. 2016, 138, 4843–4851 DOI
106. Singharoy, A.; Venkatakrishnan, B.; Liu, Y.; Mayne, C. G.; Lee, S.; Chen, C-H.; Zlotnick, A.; Shulten, K.; Flood, A. H., Macromolecular Crystallography for Synthetic Abiological Molecules: Combining xMDFF and PHENIX for Structure Determination of Cyanostar Macrocycles, J. Am. Chem. Soc. 2015, 137, 8810-8818. 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
99. Chen, T.-H.; Lee, S.; Flood, A. H.; Miljanic, O. S., How to print a crystal structure model in 3D, CrystEngComm 2014, 16, 5488–5493. OPEN ACCESS–DOI Cover Art
91. Lee, S.; Chen, C.-H.; Flood, A. H., A pentagonal cyanostar macrocycle with cyanostilbene CH donors binds anions and forms dialkylphosphate [3]rotaxanes, Nature Chem. 2013, 5, 704-710. DOI
See also the news coverage by: Chem. & Eng. News, • NSF • Analytical Scientist
2. Molecular Machines and Assemblies
Molecular robots are electromechanical machines that are integrated with feedback control systems to achieve autonomous operation at the nanoscale. This goal is increasingly becoming a reality. While many molecular actuators, in the form of molecular machines, are being realized, the true revolution in control will come once we begin to understand the mechanisms of motion. To this end, we are focused on quantifying the thermodynamics and kinetics of movement. We also contend that the integration with control systems will be facilitated with voltage-gated molecular systems. With that goal in mind, 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. . 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. See also our work on light-driven foldamers for binding and releasing anions.
128. Benson, C. R.; Maffeo, C.; Fatila, E. M.; Liu, Y.; Sheetz, E. G.; Aksimentiev, A.; Singharoy, A.; Flood, A. H., “Inchworm movement of two rings switching onto a thread by biased Brownian diffusion: a three-body problem” Proc. Natl. Acad. Sci. USA 2018,38, 9391-9396. DOI
115. Qiao, B.; Liu, Y.; Lee, S.; Pink, M.; Flood, A. H., High-yield Synthesis and Acid-base Response of Phosphate-templated [3]Rotaxanes, Chem. Commun. 2016, 52, 13675-13678. DOI
114. Benson, C. R.; Fatila, E. M.; Lee, S.; Marzo, M. G.; Pink, M.; Mills, M. B.; Preuss, K. E.; Flood, A. H., Extreme Stabilization and Redox Switching of Organic Anions and Radical Anions by Large-cavity, CH Hydrogen-Bonding Cyanostar Macrocycles, J. Am. Chem. Soc. 2016, 138, 15057-15065. DOI (See highlight in Cutting Edge Chemistry from the ACS)
109. Benson, C. R.; Share, A. I.; Marzo, M. G.; Flood, A. H., Double switching of two rings in palindromic [3]pseudorotaxanes: Cooperativity and mechanism of motion, Inorg. Chem. 2016, 55, 3767–3776 DOI
95. Benson, C. R.; Hui, A. K.; Parimal, K.; Cook, B. J.; Chen, C.-H.; Lord, R. L.; Flood, A. H.; Caulton, K. C., Amplifying the Redox Activity of a bis-Tetrazine Pincer Ligand, Dalton. 2014, 43, online. DOI
94. Manck, L. E.; Benson, C. R.; Share, A. I.; Park, H.; Vander Griend, D. A.; Flood, A. H., Self-Assembly Snapshots of a 2×2 Copper(I) Grid, Supramol. Chem. 2014, 26, accepted (Special Issue for the ISMSC-8, Arlington, VA, July 7-11, 2013)
88. Book Chapter: Benson, C. R.; Share, A. I., Flood, A. H., Bioinspired Molecular Machines, in Bioinspiration and Biomimicry in Chemistry: Reverse Engineering Nature, Ed. Swiegers, G. F., Wiley, Hoboken, 2012. ebook
85. Book Chapter: Flood, A. H.; Kaifer, A. E., Supramolecular Electrochemistry, (Volume 2: Techniques), in Supramolecular Chemistry: From Molecules to Nanomaterial, Eds. Gale, P. A.; Steed, J. W., John Wiley and Sons, 2012. DOI
78 Parimal, K.; Vyas, S.; Chen, C.-H.; Hadad, C. M.; Flood, A. H., Bond Elongation in the Anion Radical of Coordinated Tetrazine Ligands: A Crystallographic, Spectroscopic and Computational Study of a Reduced {Re(CO)3Cl} Complex, Inorg. Chim. Acta. 2011, 374, 620-626. Special Issue Dedicated to Wolfgang Kaim. DOI
68 Parimal, K.; Witlicki, E. H.; Flood, A. H., Two different classes of architectures can be interconverted by reduction of a self-sorting mixture, Angew. Chem. Int. Ed. 2010, 49, 4628-4632. DOI
67 Share, A. I.; Flood, A. H., Thinking inside and outside the box (News and Views Article), Nature Chem. 2010, 2, 349-350. DOI
66 Share, A. I.; Parimal, K.; Flood, A. H., Bi-lability is defined when one electron is used to switch between concerted and step-wise pathways in Cu(I)-based bi-stable [2/3]pseudorotaxanes, J. Am. Chem. Soc. 2010, 132, 1665-1675. DOI
62 Li, G.; Parimal, K.; Vyas, S.; Hadad, C. M.; Flood, A. H.; Glusac, K. D., Pinpointing the extent of electronic delocalization in the Re(I)-to-tetrazine charge-separated excited state using time-resolved infrared spectroscopy, J. Am. Chem. Soc. 2009, 131, 11656-11657. DOI
57 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., Reduction of a redox-active ligand drives switching in a Cu(I) pseudorotaxane by a bimolecular mechanism, J. Am. Chem. Soc. 2009, 131, 1305-1313. DOI
47 Li, Y.; Huffman, J. C.; Flood, A. H. “Can Terdentate 2,6-Bis(1,2,3-Triazol-4-yl)Pyridines form Stable Coordination Compounds?” Chem. Commun. 2007, 2692-2694. DOI
Book Chapter
* Flood, A. H.; Kaifer, A. E., Supramolecular Electrochemistry, for Supramolecular Chemistry: From Molecules to Nanomaterials, Eds. Steed, J. W.; Gale, P. A. John Wiley and Sons, in press
Collaborations on Molecular Switches
We are extending the capabilities learnt on Cu(I)-based supramolecular switches to redox-active systems of collaborators
Yi Liu
54 Koshkakaryan, G.; Parimal, K.; He, J.; Zhang, X.; Abliz, Z.; Flood, A. H.; Liu, Y., pi-Stacking enhanced dynamic and redox-switchable self-assembly of donor-acceptor metallo-[2]catenanes from diimide derivatives and crown ethers, Chem. Eur. J. 2008, 14, 10211-10218. DOI
Jan O Jeppesen
136. Andersen, S.; Saad, A. W.; Kristensen. R.; Pedersen T. S.; O’Driscoll, L. J.; Flood, A. H.; Jeppesen, J. O., Salts accelerate the switching kinetics of a cyclobis(paraquat-p-phenylene) [2]rotaxane, Org. Biol. Chem. 2019, 17, 2432-2441. DOI
98. Andersen, S. S.; Share, A. I.; Poulsen, B. L. C.; Korner, M.; Duedal, T.; Benson, C. R.; Hansen, S. W.; Jeppesen, J. O.; Flood, A. H., Mechanistic Evaluation of Motion in Redox-Driven Rotaxanes Reveal Longer Linkers Hasten Forward Escapes and Hinder Backward Translations, J. Am. Chem. Soc. 2014, 136, 6373–6384. DOI
90. Sorensen, A.; Andersen S. S.; Flood, A. H.; Jeppesen, J. O., Pressure effects in the synthesis of isomeric rotaxanes, Chem. Commun. 2013, 49, 5936–5938. DOI
87. Andersen, S. S.; Jensen, M.; Sorensen, A.; Miyazaki, E.; Takimiya, K.; Laursen, B. W.; Flood, A. H.; Jeppesen, J. O., Anion effects on the cyclobis(paraquat-p-phenyelen) host, Chem. Commun. 2012, 48, 5157-5159. DOI
82 Hansen, S. W.; Stein, P. C.; Sorensen, A.; Share, A. I.; Witlicki, E. H.; Kongsted, J.; Flood, A. H.; Jeppesen, J. O., Quantification of the pi-pi Interactions that Govern Tertiary Structure in Donor-Acceptor [2]Pseudorotaxanes, J. Am. Chem. Soc. 2012, asap. DOI
49 Nygaard, S.; Laursen, B. W.; Hansen, T. S.; Bond, A. D.; Flood, A. H.; Jeppesen, J. O., “Preparation of cyclobis(paraquat-p-phenylene)-based [2]rotaxanes without flexible glycol chains”, Angew. Chem. Int. Ed. 2007, 46, 6093-6097. DOI
48 Nygaard, S.; Hansen, S. W.; Huffman, J. C.; Jensen, F.; Flood, A. H.; Jeppesen, J. O. “Two Classes of Alongside Charge-Transfer Interactions Defined in One [2]Catenane,” J. Am. Chem. Soc. 2007, 129, 7354-7363. DOI
46 Nygaard, S.; Liu, Y.; Stein, P. C.; Flood, A. H.; Jeppesen, J. O. “Using Molecular Force to Overcome Steric Barriers in a Spring-Like Molecular Ouroborous,” Adv. Funct. Mat. 2007, 17, 751-762.
42 Nygaard, S.; Flood, A. H.; Jeppesen, J. O.; Bond, A. D. “Cis- and Trans-Bis(2-cyanoethylsulfanyl)(decane-1,10-diyldithio)Tetrathiafulvalene,” Acta. Cryst. C 2006, 62, 677-680.
3. Fluorescent Small-Molecule Ionic, Isolation Lattices (SMILES)
We discovered the brightest fluorescent materials and are exploring the underlying design rules to make optical and photonic materials. These materials are called small-molecule, ionic isolations lattices or SMILES for short. Some of our goals are to address scientific challenges around the hierarchical assembly of different molecular fluorophores into photonic materials and how the resulting packing and doping in nanoparticles and crystals can be used to understand and control the flow of excitons to productive sites for light emission and photon upconversion in solids. This approach lays the foundation for versatile, ‘plug-and-play’ photonic materials for communications, solar, display, and new quantum technologies. The start-up stemming from these materials, Halophore, stands ready to assist with commercialization.
These materials are being explored in collaboration Krishnan Raghavachari (Indiana University), Bo Laursen (University of Copenhagen, Denmark), Jerome Lacour (University of Geneva, Switzerland), Bo Albinsson (Chalmers University, Sweden), Grace Han (UC Santa Barbara), Vinod Menon (CUNY), Matt Sfeir (GaTech), Keisuje Goda (Tokyo University, Japan) and Junsheng Chen (University of Copenhagen, Denmark).
194. Chen, J.; Juhl, K.; Zhang, F.; He, Y.; Flood, A. H.; Kjaer, A.; Laursen B. W., NIR: Near-Infrared Emitting Organic Nanoparticles Based on Small-Molecule Ionic Isolation Lattices for in-vivo Imaging of Human Brain Cancer, ACS Appl. Nano Mater. 2025, XX, xxxx
192. Olsson, A. H.; Tripathy, V.; Yamamoto, N.; Usuba, J.; Leavitt, J. S.; Kambas, E. A.; VanDenburgh, K. L.; Raghavachari, K.; Laursen, B. W.; Han, G. G. D.; Flood, A. H. Bambusuril Small-Molecule Ionic Isolation Lattices using Crystal Engineering, J. Am. Chem. Soc., 2025 accepted
185. Loveless, M. K.; Che, M.; Sanchez, A. J.; Tripathy, V.; Laursen, B. W.; Pamidighantam, S.; Raghavachari, K.; Flood, A. H., Extracting Recalcitrant Redox Data on Fluorophores to Pair with Optical Data for Predicting Small-Molecule, Ionic Isolation Lattices, Digital Discovery, 2024, 3, 2105-2117.
182. Stenspil, S. G.; Olsson, A. H.; Mucci, R.; Pink, M.; Besnard, C.; Lacour, J.; Flood, A. H.; Laursen, B. W., Supramolecular Control of Helicene CPL Emitters in Molecular Solids and Bright Nanoparticles, Angew. Chem. Int. Ed. 2024, 63, e202412320
179. Tripathy, V.; Flood, A. H.; Raghavachari, K., Accelerated computer-aided screening of optical materials: Investigating the potential of ∆-SCF Methods to predict emission maxima of large dye molecules, J. Phys. Chem. A., 2024, 128, 8333-8345
178. Yadav, R. K.; Satapathy, S.; Deshmukh, P.; Datta, B.; Sharma, A.; Olsson, A. H.; Chen, J.; Laursen, B. W.; Flood, A. H.; Sfeir, M. Y.; Menon V. M., Direct Writing of Room Temperature Polariton Condensate Lattice Nano Letters, 2024, 24, 4945-4950.
176. Stenspil, S. G.; Chen, J.; Liisberg, M. B.; Flood, A. H.; Laursen, B. W., Control of the fluorescence lifetime in dye based nanoparticles, Chem. Sci. 2024, 15, 5531-5538.
175. Deshmukh, P.; Satapathy, S.; Michail, E.; Olsson, A. H.; Bushati, R.; Yadav, R. K.; Khatonair, M.; Chen, J.; John, G.; Laursen, B. W.; Flood, A. H.; Sfeir, M. Y.; Menon, V. M., A plug-and-play molecular approach for room temperature polariton condensation, ACS Photonics, 2024, 11, 348-355
170. Nishiyama,R. Furuya, K.; McCann, P.; Kacenauskaite, L.; Laursen, B. W.; Flood, A. H.; Hiramatsu, K.; Goda, K. Boosting the Brightness of Raman Tags Using Cyanostar Macrocycles, Anal. Chem. 2023, 95, 12835–12841. https://doi.org/10.1021/acs.analchem.3c01958
168. Edhborg, F.; Olesund, A.; Tripathy, V.; Wang, Y.; Sadhukhan, T.; Olsson, A. H.; Bisballe, N.; Raghavachari, K.; Laursen, B. W.; Albinsson, B.; Flood, A. H., Triplet States of Cyanostar and its Anion Complexes, J. Phys. Chem. A, 2023, 127, 5841-5850. https://doi.org/10.1021/acs.jpca.3c02701
165. Kacenauskaite, L.; Olsson, A. H.; Flood, A. H.; Laursen, B. W., Universal Concept for Bright, Organic, Solid-State Emitters-Doping of Small-Molecule Ionic Isolation Lattices with FRET, J. Am. Chem Soc. 2022, 144, 19981-19989. https://doi.org/10.1021/jacs.2c08540
163. Chen, J.; Stenspil, S. G.; Kaziannis, S.; Kacenauskaite, L.; Lenngren, N.; Kloz, M.; Flood, A. H.; Laursen, B. W., Quantitative Energy Transfer in Organic Nanoparticles Based on Small-Molecule Ionic Isolation Lattices for UV Light Harvesting, ACS Appl. Nano Mater. 2022, 5, 13887-13893. https://doi.org/10.1021/acsanm.2c01899
153. Chen, J.; Ali Fateminia, S. M.; Kacenauskaite, L.; Bærentsen, N.; Stenspil, S. G.; Bredehoeft, J.; Martinez, K. L.; Flood, A. H.; Laursen, B. W., Ultra-Bright Fluorescent Organic Nanoparticles Based on Small-Molecule Ionic Isolation Lattices, Angew. Chem. Int. Ed., 2021, 60, 9450. Hot Paper
143. Benson, C. R.; Kacenauskaite, L.; VanDenburgh, K. L.; Zhao, W.; Qiao, B.; Sadhukhan, T.; Pink, M.; Chen, J.; Borgi, S.; Chen, C.; Davis, B. J.; Simon, Y. C.; Raghavachari, K.; Laursen, B. W.; Flood, A. H., Plug-and-play Optical Materials from Fluorescent Dyes and Macrocycles, Chem, 2020. 6, 1978-1997. 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