Physical Chemistry Seminar: Prof. Tim Zuehlsdorff

About this event

" Modeling optical properties of molecules in complex environments using tensor-network approaches " Assistant Professor Tim Zuehlsdorff - Department of Chemistry, Oregon State University Host: Xiaosong Li

Theoretical spectroscopy plays a crucial role in understanding light-driven properties of materials and molecules. Truly predictive modeling of optical properties of systems in the condensed phase, such as solvated molecules, is however highly challenging, as direct couplings of the electronic states to the complex environment must be accounted for. Additionally, non-Condon effects due to vibrationally induced symmetry-breaking, or nonadiabatic effects due to multiple explicitly coupled electronic excited states influence light-induced energy relaxation dynamics in a wide range of molecular systems and are notoriously difficult to model. In this talk, I discuss a dynamic approach recently developed in our group to address this challenge, that is based on sampling fluctuations of the excitation energies and transition dipole moments of molecules in the condensed phase along ground-state molecular dynamics trajectories. Linear and nonlinear spectra are then computed in the diabatic picture, where the exact finite-temperature quantum dynamics of the system is solved using powerful tensor-network approaches. The method can yield absorption and fluorescence lineshapes, as well as time-resolved non-linear spectroscopy experiments that directly probe excited state relaxation dynamics, such as transient absorption and 2D electronic spectroscopy (2DES). I will highlight the strengths of the developed methodology by modeling absorption and time-resolved fluorescence of the proflavine molecule, establishing that gas-phase dual fluorescence in this system is quenched in solution due to solvent-driven symmetry-breaking. I will also highlight how the method allows us to uncover complex time-resolved relaxation dynamics in solvated systems like indole and DMABN. The results showcase how optical spectra and excited state relaxation dynamics of molecules with strongly interacting excited states can be highly sensitive to coupling to complex condensed phase environments.

Tim Zuehlsdorff is an associate professor in computational/theoretical physical chemistry at Oregon State University. He received his Ph.D. in theoretical physics at Imperial College London in 2015. He completed his postdoctoral training with the Cavendish Laboratory at the University of Cambridge (2014-2016) and the University of California in Merced, before joining Oregon State as a faculty member in 2020. Tim's research focuses on developing the theoretical approaches and computational methods necessary to understand how complex systems like solvated molecules, pigment-protein complexes and nanostructured materials interact with light. Specifically, he aims to understand the influence of nonadiabatic effects due to multiple coupled excited states, which he models using numerically exact tensor network approaches optimized to run on graphics processing units (GPUs). Additionally, he is interested in applying large-scale density-functional theory (DFT) methods to challenging problems in materials science related to sustainability, with examples including the direct air capture (DAC) of carbon dioxide and photochemical reactions in metal-organic frameworks (MOFs). He is a contributor to the linear-scaling electronic structure software package ONETEP, and is the author of the open-source Python package MolSpeckPy, capable of modeling linear and nonlinear optical spectroscopy experiments. His work on theoretical spectroscopy has been recognized by an NSF CAREER award (2025).