About

Professor Lin X. Chen is the principal investigator of the Chen Group in the Department of Chemistry at Northwestern University, leading a team of postdoctoral researchers and graduate students since 2008. The group operates with facilities at both Northwestern University and Argonne National Laboratory, and its members come from diverse training backgrounds including chemistry, physics, biology, and engineering. Professor Chen's research focuses on fundamental light-matter interactions in a variety of systems such as transition metal complexes, conjugated organic molecules, inorganic/organic nanostructures, and biological molecules in condensed phases, interfaces, and hybrid systems. The group employs advanced techniques including ultrafast nonlinear spectroscopy, x-ray spectroscopy, and scattering to investigate the correlations between structure, energetics, and electron and atomic dynamics in photochemical reactions. Their interdisciplinary collaborations with synthetic chemists and theorists aim to achieve a comprehensive understanding of photochemical, photophysical, and photobiological reactions. Key research themes include electron processes in solar energy conversion materials, effects of coherent electron and nuclear motions in photochemistry, and structural dynamics in biology.

Research topics

• Materials science
• Chemical engineering
• Nanotechnology
• Optoelectronics
• Organic chemistry
• Composite material
• Crystallography
• Chemistry
• Optics
• Chemical physics
• Physical chemistry
• Inorganic chemistry

Selected publications

• Encumbering the Copper(I)-Diimine Coordination Sphere with a Benzyl Group: Impact on the Stability and Photoredox Properties

  The Journal of Physical Chemistry A · 2026-01-16

  articleOpen accessCorresponding

  (where NN represents a diimine such as phenanthroline or bipyridine derivatives), are considered promising photosensitizers for various photochemical applications. However, their effectiveness is subject to several key challenges. In particular, controlling steric strain around the copper(I) center by introducing appropriate substituents (R) at the α-position of the nitrogen atoms is crucial for optimizing the excited-state properties of the complex. In brief, increasing the size of R leads to longer emission lifetimes and higher quantum yields. Additionally, the energy of the singlet excited state rises with increasing steric bulk, enhancing photoinduced reactivity. However, excessive steric strain from bulky substituents can significantly destabilize the coordination sphere. To balance complex stability with increased steric bulk around the metal center, we have developed two novel nonsymmetrical ligands featuring branched alkyl chains and benzyl groups at the α-position of the nitrogen atoms. Our findings demonstrate that intramolecular π-stacking interactions between the benzyl group and the opposing phenanthroline ligand contribute to stabilizing the coordination sphere. Furthermore, the flexibility of the benzyl group reinforces the tetrahedral geometry around copper(I), resulting in an increased singlet excited-state energy compared to benchmark complexes. Notably, we show that this enhancement in excited-state energy translates into greater excited-state reactivity.

  PublisherOA PDFDOI

• Ultrafast Dynamics of Excitonic Complexes in Electrolyte-Gated Monolayer MoS ₂

  Nano Letters · 2026-02-10

  articleSenior authorCorresponding

  Understanding and controlling ultrafast excitons and trion dynamics in monolayer transition metal dichalcogenides (TMDs) is critical for optoelectronic and photonic applications. These dynamics depend strongly on carrier density, but most studies use fluence-dependence to modulate electron–hole populations rather than direct electrostatic gating that is more relevant to optoelectronic devices. We utilize electrolyte gating to tune the ground-state carrier density of monolayer MoS2 and probe excitonic dynamics using transient absorption spectroscopy, thereby modifying absorption through bandgap renormalization, screening, phase-space filling, and exciton-trion crossover. Spectral deconvolution reveals distinct but coupled exciton and trion dynamics. Excitons form independently of voltage but relax faster with increasing carrier density, consistent with Auger-like processes, while trions decay more rapidly through multiple channels. At higher voltages, trion relaxation shifts from a subpicosecond cooling to slower trapping-assisted processes. Our results provide missing insights into the interplay between excitons and trions in monolayer MoS2, relevant for TMD-based optoelectronics.

  PublisherDOI

• Tracking Photoinduced Charge Redistribution in a Cu(I) Diimine Donor–Bridge–Acceptor System with Time-Resolved Infrared Spectroscopy

  Photochem · 2025-06-19 · 1 citations

  articleOpen accessSenior authorCorresponding

  Understanding electron density migration along excited-state pathways in photochemical systems is critical for optimizing solar energy conversion processes. In this study, we investigate photoinduced electron transfer (PET) in a covalently linked donor–bridge–acceptor (D-B-A) system, where [Cu(I)-bis(1,10-phenanthroline)]+ acts as an electron donor, and anthraquinone, tethered to one of the phenanthroline ligands via a vibrationally active ethyne bridge, behaves as an electron acceptor. Visible transient absorption spectroscopy revealed the dynamic processes occurring in the excited state, including PET to the acceptor species. This was indicated by the spectral features of the anthraquinone radical anion that appeared on a timescale of 30 ps in polar solvents. Time-resolved infrared (TRIR) spectroscopy of the alkyne vibration (CC stretch) of the ethyne bridge provided insight into electronic structural changes in the metal-to-ligand charge transfer (MLCT) state and along the PET reaction coordinate. The observed spectral shift and enhanced transition dipole moment of the CC stretch demonstrated that there was already partial delocalization to the anthraquinone acceptor following MLCT excitation, verified by DFT calculations. An additional excited-state TRIR signal unrelated to the vibrational mode highlighted delocalization between the phenanthroline ligands in the MLCT state. This signal decayed and the CC stretch narrowed and shifted towards the ground-state frequency following PET, indicating a degree of localization onto the acceptor species. This study experimentally elucidates charge redistribution during PET in a Cu(I) diimine D-B-A system, yielding important information on the ligand design for optimizing PET reactions.

  PublisherOA PDFDOI

• Superadditivity of Convex Roof Coherence Measures in Multipartite System

  ArXiv.org · 2025-05-19

  preprintOpen accessSenior author

  In this paper, we investigate the convex roof measure of quantum coherence, with a focus on their superadditive properties. We propose sufficient conditions and establish a framework for coherence superadditivity in tripartite and multipartite systems. Through theoretical derivation, the relevant theorems are given. These results not only expand our understanding of the superadditivity of pure and mixed states but also characterize the conditions under which the superadditivity relations reach equality. Finally, the proposed methods and conclusions are verified through representative examples, providing new theoretical insights into the distribution of quantum coherence in multi-part systems.

  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 accessSenior author

  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

• Research on the Impact of Algorithm-Mediated Social Media Search on Cognitive Construction

  Communications in Humanities Research · 2025-07-11

  articleOpen access1st authorCorresponding

  With the development of the social media, the character of search-engine gradually becomes more apparent. Nowadays many people tend to search for answers on social media when they meet problems. This paper explores the impact of the behavior of searching information on social media on cognitive constructions with the mediation role of algorithm. This study mainly collected data through questionnaire surveys, and then used if for correlation analysis and mediation analysis. The findings indicate that the behavior of searching information on social media play a positive role in cognitive construction and the algorithm serves as a partial intermediary factor in the relationship between them. In the era of big data, with the development of the information pushed by algorithms, people gradually turn from searching information in traditional search engines (one-way reception) to the social media platforms (two-way interaction), which change peoples cognitive constructions. This study will be helpful and instructive for the development of social media and the AI smart search launched in recent years.

  PublisherOA PDFDOI

• Spin-Vibronic Effect in Photoinduced Electron Transfer

  The Journal of Physical Chemistry Letters · 2025-11-03

  articleSenior authorCorresponding

  The spin-vibronic effect (SVE) accelerates quantum-mechanically forbidden electronic transitions, but experimental manifestations of this phenomenon remain limited. In this contribution, the role of SVE in photoinduced electron transfer (PET) dynamics is probed by coherent vibrational wavepacket (CVWP) motions in Pt(II) dimer-naphthalene diimide donor–acceptor complexes. Metal–metal-to-ligand charge-transfer (MMLCT) excitation of the donor triggers ballistic PET, driving the molecule away from equilibrium. The SVE then directs the PET trajectory from the 1MMLCT excited state to an intermediate ligand-centered triplet state, modulating the CVWP dynamics along the reaction coordinates. Herzberg–Teller type oscillations indicate that the Pt–Pt stretching vibration, arising from the formation of the excited triplet intermediate, serves as the reaction coordinate for charge separation. Our experimental findings advance the understanding of the interplay between electronic, vibrational, and spin degrees of freedom in ultrafast photoactivated processes.

  PublisherDOI

• Ultrafast hydrogen-bonding interactions between a photoexcited Cu–anthraquinone donor–acceptor dyad and protic solvents

  The Journal of Chemical Physics · 2025-06-04 · 1 citations

  articleSenior author

  The rational design of solar energy catalysts requires a mechanistic understanding of the ultrafast interactions with the solvent environment. We have designed a new Cu(I)-anthraquinone framework (CuEthyneAnQ) to serve as a model for studying hydrogen-bonding effects in charge accumulating photocatalysts. Herein, we report the ground and excited-state characterization of CuEthyneAnQ by electrochemical and ultrafast optical transient absorption (OTA) spectroscopy measurements. Significant stabilization of the AnQ-centered reductions due to hydrogen-bonding was observed by electrochemical measurements in protic solvent mixtures. Analysis of the excited-state photophysics with OTA reveals electron transfer occurring in tens of picoseconds after metal-to-ligand charge transfer excitation, resulting in the charge-separated state of Cu(II)EthyneAnQ·-. Charge recombination occurs in 4 ns in aprotic solvent and extends to 19 ns in protic solvent. In order to examine the influence of hydrogen-bonding on the electron-transfer dynamics, we performed OTA measurements on CuEthyneAnQ in varying aprotic:protic solvent mixtures. We observe three effects that depend on the concentration of the protic solvent: (1) after charge separation, a diffusion-limited hydrogen-bond forms with the reduced AnQ·-; (2) the slowdown in charge recombination with protic solvent addition is due to hydrogen-bond stabilization in accordance with Marcus theory; and (3) a spectral shift occurs in the charge-separated state due to an increasing number of hydrogen-bond interactions. Our results are supported by time-dependent density functional theory calculations with explicit solvent hydrogen-bonding interactions. These insights underscore the potential of Cu-based donor-acceptor complexes and mixed-solvent systems to offer valuable guidelines for the design of more efficient photocatalytic systems.

  PublisherDOI

• Dependence of Exciton Spin Dynamics on Quantum Confinement Dimensionality in CsPbBr₃ Nanocrystals

  Nano Letters · 2025-04-28 · 5 citations

  article

  nanospheres, cubes, and rods spanning the zero-dimensional (0D) to three-dimensional (3D) transition to investigate the influence of dimensionality and shape on exciton spin decoherence. Using circularly polarized transient absorption spectroscopy, we find that the spin relaxation rate is independent of the surface to volume ratio and instead follows a dependence on the length of the shortest dimension. Additionally, differences in surface quality and termination appear to have no effect on the spin relaxation rate for measured materials, and instead the spin relaxation rate is most clearly correlated with the exciton binding energy. Finally, decreasing the dimensionality of the nanomaterials decreases the influence of multiexciton interactions on the spin relaxation rate.

  PublisherDOI

• Photochemical CO₂ Reduction by a Postsynthetically Modified Zr-MOF

  Inorganic Chemistry · 2025-08-29 · 4 citations

  article

  Metal–organic frameworks are an excellent platform for photochemical CO2 reduction into valuable chemicals. Herein, we report the synthesis and photocatalytic behavior of Ru@MOF-808, a Zr-based MOF, modified with a Ru-polypyridyl complex. The postsynthetic modification was achieved using solvent-assisted incorporation of bipyridine–carboxylate ligands onto the nodes of the MOF-808, followed by the coordination of Ru(II)-terpyridine moiety. A thorough characterization including 1H NMR, diffuse reflectance UV/vis, X-ray absorption spectroscopy and gas adsorption studies, combined with DFT calculations, provides strong support for efficient incorporation of the molecular Ru-complex at the loading of one Ru center per node. In the presence of a strong sacrificial reductant BIH, Ru@MOF-808 was found to catalyze the photochemical reduction of CO2 into a mixture of CO and formate ion. When compared to the homogeneous model catalyst Ru(tpy)(bpy)2+, Ru@MOF-808 was found to exhibit higher formate yields. To explain these formate enhancements, we propose a mechanism that involves CO2 capture at the MOF nodes to form Zr-bicarbonate species, which further react in a hydride transfer reaction with photogenerated Ru–H donor, thereby outperforming molecular catalysts in HCOO– production. Overall, the results presented in this work indicate the potential of Zr-based MOFs in integrating CO2 capture with its photochemical conversion to desired products.

  PublisherDOI

Recent grants

• Capturing Transient Protein and Nucleic Acid Structures During Their Functions on Multiple Spatial and Temporal Scales

  NIH · $3.0M · 2015–2025

• CAS: Collaborative Research: Mapping Excited State Trajectories of Multi-metal Centered Complexes by Two-Dimensional Electronic Spectroscopy

  NSF · $300k · 2023–2026

• SEP Collaborative: Development of Economically Viable, Highly Efficient Organic Photovoltaic Solar Cells

  NSF · $450k · 2012–2016

• Collaborative Research: Electronic Coherence Effects in Multichromophore Systems Probed by Two-Dimensional Electronic Spectroscopy

  NSF · $275k · 2020–2023

• Collaborative Research: Ultrafast Excited State Electron and Nuclear Coherences in Transition Metal Dimer Complexes and Their Roles in Photochemistry

  NSF · $275k · 2017–2020

Frequent coauthors

• Michael W. Mara

  Stanford University

  128 shared

• Tobin J. Marks

  Northwestern University

  109 shared

• Eric F. Manley

  Kennesaw State University

  98 shared

• Richard D. Schaller

  97 shared

• Jodi M. Szarko

  Lafayette College

  94 shared

• Xiaoyi Zhang

  Guangzhou Medical University

  91 shared

• Luping Yu

  Peking University People's Hospital

  82 shared

• Brian S. Rolczynski

  United States Naval Research Laboratory

  81 shared

Labs

• The Chen GroupPI

Education

• Ph.D., Physical Chemistry

  The University of Chicago

  1987

• B.S., Chemistry

  Peking University

  1982