About

Kevin Kohlstedt is a Research Professor in the Department of Chemistry at Northwestern University, based in Evanston, Illinois. His research focuses on charge transport in disordered materials, photovoltaic design using data analytics, plasmonic coupling of self-assembled superstructures, and the self-assembly of anisotropic colloids. As a research associate professor, he contributes to advancing understanding in these areas through experimental and analytical approaches, supporting the development of novel materials and technologies in the field of chemistry.

Research topics

• Organic chemistry
• Chemistry
• Materials science
• Photochemistry
• Crystallography
• Composite material
• Physical chemistry
• Nanotechnology
• Chemical engineering
• Medicinal chemistry
• Engineering
• Electrical engineering
• Physics

Selected publications

• Nanotechnology for catalysis and solar energy conversion

  UNC Libraries · 2025-10-31

  articleOpen access

  This roadmap on Nanotechnology for Catalysis and Solar Energy Conversion focuses on the application of nanotechnology in addressing the current challenges of energy conversion: 'high efficiency, stability, safety, and the potential for low-cost/scalable manufacturing' to quote from the contributed article by Nathan Lewis. This roadmap focuses on solar-to-fuel conversion, solar water splitting, solar photovoltaics and bio-catalysis. It includes dye-sensitized solar cells (DSSCs), perovskite solar cells, and organic photovoltaics. Smart engineering of colloidal quantum materials and nanostructured electrodes will improve solar-to-fuel conversion efficiency, as described in the articles by Waiskopf and Banin and Meyer. Semiconductor nanoparticles will also improve solar energy conversion efficiency, as discussed by Boschloo et al in their article on DSSCs. Perovskite solar cells have advanced rapidly in recent years, including new ideas on 2D and 3D hybrid halide perovskites, as described by Spanopoulos et al 'Next generation' solar cells using multiple exciton generation (MEG) from hot carriers, described in the article by Nozik and Beard, could lead to remarkable improvement in photovoltaic efficiency by using quantization effects in semiconductor nanostructures (quantum dots, wires or wells). These challenges will not be met without simultaneous improvement in nanoscale characterization methods. Terahertz spectroscopy, discussed in the article by Milot et al is one example of a method that is overcoming the difficulties associated with nanoscale materials characterization by avoiding electrical contacts to nanoparticles, allowing characterization during device operation, and enabling characterization of a single nanoparticle. Besides experimental advances, computational science is also meeting the challenges of nanomaterials synthesis. The article by Kohlstedt and Schatz discusses the computational frameworks being used to predict structure-property relationships in materials and devices, including machine learning methods, with an emphasis on organic photovoltaics. The contribution by Megarity and Armstrong presents the 'electrochemical leaf' for improvements in electrochemistry and beyond. In addition, biohybrid approaches can take advantage of efficient and specific enzyme catalysts. These articles present the nanoscience and technology at the forefront of renewable energy development that will have significant benefits to society.

  PublisherDOI

• Unfolding of the Villin Headpiece Domain: Revealing Structural Heterogeneity with Time‐Resolved X‐Ray Solution Scattering and Markov State Modeling

  ChemPhysChem · 2025-04-07 · 1 citations

  articleOpen accessSenior authorCorresponding

  Understanding protein folding pathways is crucial to deciphering the principles of protein structure and function. Here, the unfolding dynamics of the 35-residue villin headpiece (HP35) and a norleucine-substituted variant (2F4K) using a combination of experimental and computational techniques is investigated. Time-resolved X-ray solution scattering coupled with equilibrium molecular dynamics simulations and Markov state modeling reveals distinct unfolding mechanisms between the two variants: HP35 and 2F4K. Specifically, HP35 exhibits a two-state unfolding process, whereas an intermediate state is identified for the 2F4K mutant. A Markov state model constructed from simulations is used to map atomic-level transitions to experimental observations, providing insights into the role of sequence variations in modulating folding pathways. The findings underscore the importance of integrating experimental and computational approaches to unravel protein unfolding mechanisms between heterogenous structural ensembles.

  PublisherOA PDFDOI

• Resolving Structural Dynamics in Biological Macromolecules with Time-resolved X-ray Solution Scattering and Molecular Dynamics Simulation

  Structural Dynamics · 2025-03-01

  articleOpen access

  The functionality of biomacromolecules, such as proteins and nucleic acids, is intricately linked to their three-dimensional (3D) structures, which are dictated by the 1D sequences of amino acids or nucleotides. The process by which a 1D sequence folds into a functional 3D structure has been a longstanding challenge in molecular biology. While significant progress has been made in understanding the intrinsic forces that govern this transformation, our comprehension remains limited regarding how external factors, including pH, temperature, metal ion coordination, and concentration, influence the formation of 3D structures through interactions with the macromolecular environment.

  PublisherDOI

• Hydrogen-Bonded Fibrous Nanotubes Assembled from Trigonal Prismatic Building Blocks

  Journal of the American Chemical Society · 2024-07-29 · 8 citations

  article

  In reticular chemistry, molecular building blocks are designed to create crystalline open frameworks. A key principle of reticular chemistry is that the most symmetrical networks are the likely outcomes of reactions, particularly when highly symmetrical building blocks are involved. The strategy of synthesizing low-dimensional networks aims to reduce explicitly the symmetry of the molecular building blocks. Here we report the spontaneous formation of hydrogen-bonded fibrous structures from trigonal prismatic building blocks, which were designed to form three-dimensional crystalline networks on account of their highly symmetrical structures. Utilizing different microscopic and spectroscopic techniques, we identify the structures at the early stages of the assembly process in order to and understand the growth mechanism. The symmetrical molecular building blocks are incorporated preferentially in the longitudinal direction, giving rise to anisotropic hydrogen-bonded porous organic nanotubes. Entropy-driven anisotropic growth provides micrometer-scale unidirectional nanotubes with high porosity. By combining experimental evidence and theoretical modeling, we have obtained a deep understanding of the nucleation and growth processes. Our findings offer fundamental insight into the molecular design of tubular structures. The nanotubes evolve further in the transverse directions to provide extended higher-order fibrous structures [nano- and microfibers], ultimately leading to large-scale interconnected hydrogen-bonded fiber-like structures with twists and turns. Our work provides fundamental understanding and paves the way for innovative molecular designs in low-dimensional networks.

  PublisherDOI

• Early Folding Dynamics of i-Motif DNA Revealed by pH-Jump Time-Resolved X-ray Solution Scattering

  Journal of the American Chemical Society · 2024-11-28 · 10 citations

  articleOpen accessCorresponding

  The i-motif is a pH-responsive cytosine-rich oligonucleotide sequence that forms, under acidic conditions, a quadruplex structure. This tunable structural switching has made the i-motif a useful platform for designing pH-responsive nanomaterials. Despite the widespread application of i-motif DNA constructs as biomolecular switches, the mechanism of i-motif folding on the atomic scale has yet to be established. We investigate the early folding structural dynamics of i-motif oligonucleotides with laser-pulse-induced pH-jump time-resolved X-ray solution scattering. Following the pH-jump, we observe that the initial random coil ensemble converts into a contracted intermediate state within 113 ns followed by further folding on the 10 ms time scale. We reveal the representative structures of these transient species, hitherto unknown, with molecular dynamics simulations and ensemble fitting. These results pave the way for understanding metastable conformations of i-motif folding and for benchmarking emerging theoretical models for simulating noncanonical nucleic acid structures.

  PublisherOA PDFDOI

• Elucidating performance degradation mechanisms in non-fullerene acceptor solar cells

  Journal of Materials Chemistry A · 2024-01-01 · 7 citations

  articleOpen accessCorresponding

  Degradation of Y6-based organic solar cells involves Y6 vinyl oxidation, with the resulting trap states disrupting cell performance even at very low concentrations.

  PublisherOA PDFDOI

• Control over Charge Separation by Imine Structural Isomerization in Covalent Organic Frameworks with Implications on CO₂ Photoreduction

  Journal of the American Chemical Society · 2024-02-08 · 96 citations

  articleOpen access

  Two-dimensional covalent organic frameworks (COFs) are an emerging class of photocatalytic materials for solar energy conversion. In this work, we report a pair of structurally isomeric COFs with reversed imine bond directions, which leads to drastic differences in their physical properties, photophysical behaviors, and photocatalytic CO2 reduction performance after incorporating a Re(bpy)(CO)3Cl molecular catalyst through bipyridyl units on the COF backbone (Re-COF). Using the combination of ultrafast spectroscopy and theory, we attributed these differences to the polarized nature of the imine bond that imparts a preferential direction to intramolecular charge transfer (ICT) upon photoexcitation, where the bipyridyl unit acts as an electron acceptor in the forward imine case (f-COF) and as an electron donor in the reverse imine case (r-COF). These interactions ultimately lead the Re-f-COF isomer to function as an efficient CO2 reduction photocatalyst, while the Re-r-COF isomer shows minimal photocatalytic activity. These findings not only reveal the essential role linker chemistry plays in COF photophysical and photocatalytic properties but also offer a unique opportunity to design photosensitizers that can selectively direct charges.

  PublisherOA PDFDOI

• Unlocking the unfolded structure of ubiquitin: Combining time-resolved x-ray solution scattering and molecular dynamics to generate unfolded ensembles

  The Journal of Chemical Physics · 2024-07-15 · 2 citations

  articleOpen access

  The unfolding dynamics of ubiquitin were studied using a combination of x-ray solution scattering (XSS) and molecular dynamics (MD) simulations. The kinetic analysis of the XSS ubiquitin signals showed that the protein unfolds through a two-state process, independent of the presence of destabilizing salts. In order to characterize the ensemble of unfolded states in atomic detail, the experimental XSS results were used as a constraint in the MD simulations through the incorporation of x-ray scattering derived potential to drive the folded ubiquitin structure toward sampling unfolded states consistent with the XSS signals. We detail how biased MD simulations provide insight into unfolded states that are otherwise difficult to resolve and underscore how experimental XSS data can be combined with MD to efficiently sample structures away from the native state. Our results indicate that ubiquitin samples unfolded in states with a high degree of loss in secondary structure yet without a collapse to a molten globule or fully solvated extended chain. Finally, we propose how using biased-MD can significantly decrease the computational time and resources required to sample experimentally relevant nonequilibrium states.

  PublisherOA PDFDOI

• Wavelength-Dependent Excitonic Properties of Covalent Organic Frameworks Explored by Theory and Experiments

  The Journal of Physical Chemistry C · 2023-06-15 · 4 citations

  articleOpen accessCorresponding

  Many aspects of the correlation between the physical structure, light harvesting, and excitonic properties of covalent organic frameworks (COFs) remain unclear despite being key properties determining their photocatalytic function. One area of COF research that could bring clarity is using both electronic structure theory and time-resolved spectroscopic analysis over a series of systematically varied COFs. Here, we show structure–property relationships between four imine COFs built from a combination of ditopic and tritopic monomers using transient absorption spectroscopy together with time-dependent density functional theory. We find that monomer selection only moderately affects the charge transfer (CT) behavior of the COFs. Instead, we infer that imine chemistry profoundly impacts CT by acting as a CT mediator. Moreover, we discover two distinct valence bands arising from varying degrees of locally excited/CT mixing, which is responsible for energy-dependent exciton dynamics. Finally, we use theory to hypothesize that interlayer interactions can modify excitonic properties that we correlate with tail states commonly observed but rarely investigated in COFs. These results reveal that imine chemistry should be recognized as a very important factor to consider in the development of COF photocatalysts and the correlation of their structural environment with light-harvesting and CT properties that should ultimately determine their photocatalytic function.

  PublisherOA PDFDOI

• CCDC 2181313: Experimental Crystal Structure Determination

  The Cambridge Structural Database · 2023-02-24

  datasetOpen access

  An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

  PublisherDOI

Frequent coauthors

• George C. Schatz

  Northwestern University

  92 shared

• Tobin J. Marks

  Northwestern University

  62 shared

• Antonio Facchetti

  Georgia Institute of Technology

  62 shared

• Leighton O. Jones

  45 shared

• Michael R. Wasielewski

  Northwestern University

  43 shared

• Dean M. DeLongchamp

  Material Measurement Laboratory

  35 shared

• Mark C. Hersam

  Northwestern University

  35 shared

• S. Mukherjee

  33 shared

Labs

• Kohlstedt GroupPI