Science

“At the heart of science is an essential balance between two seemingly contradictory attitudes—an openness to new ideas, no matter how bizarre or counterintuitive they may be, and the most ruthless skeptical scrutiny of all ideas, old and new.” -Carl Sagan

My research interests embrace organic chemistry, materials science, energy, and biomedical engineering.

Tattoo Innovation

We engineer intradermal tattoos that give new abilities to humans. By re-inventing the materials that make up tattoo pigments, we can create permanent or semi-permanent tattoos that change color or introduce new functions in skin, endowing it with extra sensing abilities or physical properties. Watch the TEDx talk. Watch the Bufftalk. See this work featured in Chemical & Engineering News, Inked Magazine, CBS News, Colorado Pubic Radio, ACS Central Science, KUNC, Newsy, Daily Mail, and CU Boulder Today. We are also inventing new tattooing devices that are safer, faster, cheaper, and less painful than traditional tattooing methods.

CJ Bruns. The Rise of Smart Tattoos. TEDxMileHigh, 2019.

ARTIFICIAL MOLECULAR MACHINES

We use the tools of organic chemistry to design and build some of the smallest machines known to humankind.

Molecular Muscles: Daisy Chain Rotaxanes. The convergence of sophisticated mechanically bonded molecular architectures with the stimulus-responsive properties of their underlying donor-acceptor recognition motifs has allowed us to prepare macromolec… — **Molecular Muscles: Daisy Chain Rotaxanes.** The convergence of sophisticated mechanically bonded molecular architectures with the stimulus-responsive properties of their underlying donor-acceptor recognition motifs has allowed us to prepare macromolecules that expand and contract (similar to the repeating units of muscle tissue) in response to a variety of energy sources, including electrochemical, thermal, and mechanical stimuli.
***CJ Bruns***, JF Stoddart. Rotaxane-Based Molecular Muscles. *Acc. Chem. Res.* **2014**, 47, 2186–2199
***CJ Bruns***, M Frasconi, J Iehl, KJ Hartlieb, ST Schneebeli, C Cheng, SI Stupp, JF Stoddart. Redox Switchable Daisy Chains Driven by Radical-Radical Interactions. *J. Am. Chem. Soc.* **2014**, *136*, 4714–4723
***CJ Bruns***, J Li, M Frasconi, ST Schneebeli, J Iehl, H-P Jacquot de Rouville, SI Stupp, GA Voth, JF Stoddart. An Electrochemically and Thermally Switchable Donor-Acceptor [c2]Daisy Chain Rotaxane. *Angew. Chem., Int. Ed.* **2014**, 53, 1953–1958
***CJ Bruns***, JF Stoddart. Molecular Machines Muscle Up. *Nature Nanotech.* **2013**, 8, 9–10

Molecular Accordions: Oligorotaxane Foldamers. We have designed a series of oligorotaxanes in which the axle of the dumbbell adopts a well-defined folding pattern as it “snakes” its way through a series of rings. These compounds behave like accordio… — **Molecular Accordions: Oligorotaxane Foldamers.** We have designed a series of oligorotaxanes in which the axle of the dumbbell adopts a well-defined folding pattern as it “snakes” its way through a series of rings. These compounds behave like accordions that can be mechanically unfolded and re-folded at the single-molecule level by the cantilever of an atomic force microscope. The nano-folders exert forces that exceed those of biological molecular machines in both magnitude and speed.
D Sluysmans, S Hubert, CJ ***Bruns***, Z Zhu, JF Stoddart, A-S Duwez. Synthetic Oligorotaxanes Exert High Forces When Folding Under Mechanical Load. *Nature Nanotech.* **2018**, 13, 209–213
D Sluysmans, F Devaux, CJ ***Bruns***, JF Stoddart, A-S Duwez. Dynamic Force Spectroscopy of Synthetic Oligorotaxane Foldamers. *Proc. Natl. Acad. Sci. U.S.A*. **2018**, *115*, 9362–9366
***CJ Bruns***, JF Stoddart. Mechanically Interlaced and Interlocked Donor-Acceptor Foldamers. *Adv. Polym. Sci.* **2013**, *261*, 271–294
Z Zhu, CJ ***Bruns***, H Li, J Lei, C Ke, Z Liu, S Shafaie, HM Colquhoun, JF Stoddart. Synthesis and Solution-State Dynamics of Donor-Acceptor Oligorotaxane Foldamers. *Chem. Sci.* **2013**, 4, 1470–1483

Gated Molecular Flasks. We created tiny nano-containers which, when dissolved in solution, regulate the traffic of ring-shaped molecules that bind to sites in their inner cavities. The flasks are “gated” in the sense that they only permit the rings … — **Gated Molecular Flasks.** We created tiny nano-containers which, when dissolved in solution, regulate the traffic of ring-shaped molecules that bind to sites in their inner cavities. The flasks are “gated” in the sense that they only permit the rings entrance in the presence of excessive ions, not unlike many ion channels in the membranes of living cells.
***CJ Bruns***, D Fujita, M Hoshino, S Sato, JF Stoddart, M Fujita. Emergent Ion-Gated Binding of Cationic Host-Guest Complexes Within Cationic M12L24 Molecular Flasks. *J. Am. Chem. Soc.* **2014**, *136*, 12027–12034

Switchable Contrast Agents. We have developed molecular machines that use the energy of a chemical reaction to activate a signal that can be detected by an MRI machine. Specifically, we created rotaxanes that release cucurbit[6]uril, a contrast agen… — **Switchable Contrast Agents.** We have developed molecular machines that use the energy of a chemical reaction to activate a signal that can be detected by an MRI machine. Specifically, we created rotaxanes that release cucurbit[6]uril, a contrast agent for hyperpolarized xenon, in response to chemical and biochemical signals. These little single-use nanomachines enable chemical and biochemical events to be detected with ultra-high sensitivity.
JA Finbloom, CC Slack, CJ ***Bruns***, K Jeong, DE Wemmer, A Pines, MB Francis. Rotaxane-Mediated Suppression and Activation of Cucurbit[6]uril for Molecular Detection by 129Xe HyperCEST NMR. *Chem. Commun.* **2016**, 52, 3119–3122
CC Slack, JA Finbloom, K Jeong, CJ ***Bruns***, DE Wemmer, A Pines, MB Francis. Rotaxane Probes for Protease Detection by 129Xe HyperCEST NMR. *Chem. Commun*. **2017**, 53, 1076–1079

Self-Assembling Energy Materials

We create molecules with built-in interactions that guide their self-assembly into functional structures that can harvest and channel energy.

Self-Assembling Inks for Plastic Solar Cells. We have developed a number of families of small-molecule p-type organic semiconductors for solution-processed photovoltaics, with the aim of understanding the structure-property relationships underpinnin… — **Self-Assembling Inks for Plastic Solar Cells.** We have developed a number of families of small-molecule p-type organic semiconductors for solution-processed photovoltaics, with the aim of understanding the structure-property relationships underpinning the performance of these materials in low-cost, printable solar cells. We have designed the compounds to self-assemble into structures that facilitate photocurrent generation in order to enhance their efficiency.
S Loser, SJ Lou, BM Savoie, CJ **Bruns**, A Timalsina, MJ Leonardi, T Harschneck, R Turrisi, N Zhou, CL Stern, AA Sarjeant, A Facchetti, RPH Chang, SI Stupp, MA Ratner, LX Chen, TJ Marks. Systematic Evaluation of Structure-Property Relationships in Heteroacene-Diketopyrrolopyrrole Molecular Donors for Organic Solar Cells. *J. Mater. Chem. A* **2017***, 5*, 9217–9232
T Aytun, PJ Santos, CJ **Bruns**, D Huang, AR Koltonow, M Olvera de la Cruz, SI Stupp. Self-Assembling Tripodal Small-Molecule Donors for Bulk Heterojunction Solar Cells. *J. Phys. Chem. C* **2016**, *120*, 3602–3611
A Ruiz-Carretero, T Aytun, CJ **Bruns**, CJ Newcomb, W-W Tsai, SI Stupp. Stepwise Self-Assembly to Improve Solar Cell Morphology. *J. Mat. Chem. A* **2013**, 1, 11674–11681
A Guerrero, SC Loser, G Garcia-Belmonte, CJ **Bruns**, J Smith, H Miyauchi, SI Stupp, TJ Marks, J Bisquert. Solution-Processed Small Molecule: Fullerene Bulk-Heterojunction Solar Cells: Impedance Spectroscopy Deduced Bulk and Interfacial Limits to Fill-Factor. *Phys. Chem. Chem. Phys.* **2013**, 15, 16456–16462
S Loser, CJ **Bruns**, H Miyauchi, R Ponce Ortiz, A Facchetti, SI Stupp, TJ Marks. A Naphthodithiophene-Diketopyrrolopyrrole Donor Molecule for Efficient Solution-Processed Solar Cells. *J. Am. Chem. Soc.* **2011**, *133,* 8142–8145

Self-Assembling Inorganic-Organic Hybrid Photoconductors. We systematically studied a series of semiconducting surfactants that can be co-assembled with ZnO into photoconducting inorganic-organic hybrid lamellar nanostructures by electrodeposition. … — **Self-Assembling Inorganic-Organic Hybrid Photoconductors.** We systematically studied a series of semiconducting surfactants that can be co-assembled with ZnO into photoconducting inorganic-organic hybrid lamellar nanostructures by electrodeposition. We unconvered molecular design rules for controlling the long-range orientation of these nanostructures.
**CJ Bruns**, DJ Herman, JB Minuzzo, JA Lehrman, SI Stupp. Rationalizing Molecular Design in Electrodeposition of Anisotropic Lamellar Nanostructures. *Chem. Mater.* **2013**, 25, 4330–4339

Mechanomolecules

In molecules, the mechanical bond is not shared between atoms—it is a bond that arises when molecular entities become entangled in space. This emergent bond endows matter with a whole suite of novel properties relating to both form and function. They hold unlimited promise for countless applications, ranging from their presence in molecular devices and electronics to their involvement in advanced functional materials. I have investigated the synthesis, structures, properties, and dynamics of molecules with mechanical bonds, or mechanomolecules, for more than a decade.

The Nature of the Mechanical Bond is a comprehensive book reviewing of much of the contemporary literature (>3000 unique references) on the mechanical bond through 2016, accessible to newcomers and veterans alike. Topics covered include: – Supram… — **The Nature of the Mechanical Bond** is a comprehensive book reviewing of much of the contemporary literature (>3000 unique references) on the mechanical bond through 2016, accessible to newcomers and veterans alike. Topics covered include:
– Supramolecular, covalent, and statistical approaches to the formation of entanglements that underpin mechanical bonds in molecules and macromolecules
– Kinetically and thermodynamically controlled strategies for synthesizing mechanomolecules
– Chemical topology, molecular architectures, polymers, crystals, and materials with mechanical bonds
– The stereochemistry of the mechanical bond (mechanostereochemistry), including the novel types of dynamic and static isomerism and chirality that emerge in mechanomolecules
– Artificial molecular switches and machines based on the large-amplitude translational and rotational motions expressed by suitably designed catenanes and rotaxanes.
This contemporary and highly interdisciplinary field is summarized in a visually appealing, image-driven format, with more than 800 illustrations covering both fundamental and applied research. *The Nature of the Mechanical Bond* is a must-read for everyone, from students to experienced researchers, with an interest in chemistry’s latest and most non-canonical bond.
**CJ Bruns**, JF Stoddart, *The Nature of the Mechanical Bond: From Molecules to Machines*. Hoboken: John Wiley & Sons, 2016. 761 pp. ISBN: 9781119044000

Slide-Ring Polymers

We work on a novel class of so-called slide-ring polymers that possess a “beads-on-a-string” architecture, in which the motion of the beads on the polymer strings endow these materials (e.g., gels, glasses) with remarkable mechanical and rheological properties.

CJ Bruns. Exploring and Exploiting the Symmetry-Breaking Effect of Cyclodextrins in Mechanomolecules. Symmetry 2019, 11, 1249–1271
Z Zhu, CJ Bruns, H Li, J Lei, C Ke, Z Liu, S Shafaie, HM Colquhoun, JF Stoddart. Synthesis and Solution-State Dynamics of Donor-Acceptor Oligorotaxane Foldamers. Chem. Sci. 2013, 4, 1470–1483
CM Gothard, CJ Bruns, NA Gothard, BA Grzybowski, JF Stoddart. Modular Synthesis of Bipyridinium Oligomers and Corresponding Donor-Acceptor Oligorotaxanes with Crown Ethers. Org. Lett. 2012, 14, 5066–5069

Mechanically Bonded Protein Bioconjugates. We have developed near-quantitative synthetic protocols for the aqueous synthesis of rotaxanes and protein-mounted rotaxanes by employing efficient bioconjugation reactions. These molecules represent the fi… — **Mechanically Bonded Protein Bioconjugates.** We have developed near-quantitative synthetic protocols for the aqueous synthesis of rotaxanes and protein-mounted rotaxanes by employing efficient bioconjugation reactions. These molecules represent the first protein-rotaxane hybrid molecules and set the stage for artificial molecular machines that work together with biological molecular machines. I don’t understand why my intellectual contribution wasn’t acknowledged by my collaborators in the second paper listed below, but hey, it happens.
**CJ Bruns**, H Liu, MB Francis. Near-Quantitative Aqueous Synthesis of Rotaxanes via Bioconjugation to Oligopeptides and Proteins. *J. Am. Chem. Soc.* **2016**, *138*, 15307–15310
JA Finbloom, K Han, CC Slack, AL Furst, MB Francis. Cucurbit[6]uril-Promoted Click Chemistry for Protein Modification. *J. Am. Chem. Soc.* **2017**, *139*, 9691–9697.

Robochemistry

Our interdisciplinary team is working on robots that can automate many procedures in the chemistry lab. These robots will provide many benefits: making organic synthesis safer for humans, enabling chemistry to be done remotely in the post-COVID age, and saving lots of time, money, resources, and energy in the lab.