The Zuerch Lab at the University of California at Berkeley experimentally explores structural, carrier and spin dynamics in novel quantum materials, heterostructures and at material interfaces to answer current questions in materials science and physical chemistry. For this we pursue a multidisciplinary research program that combines the exquisite possibilities that ultrafast X-ray spectroscopy and nanoimaging offers and closely interface with material synthesis and theory groups. We employ state-of-the-art methods and develop novel nonlinear X-ray spectroscopies in our lab and at large-scale facilities. Specifically, we are interested in experimentally studying and controlling material properties on time scales down to the sub-femtosecond regime and on nanometer length scales to tackle challenging problems in quantum electronics, information storage and solar energy conversion.
Learn more about our research.
Under mild blue-light irradiation, α-acylated saturated heterocycles undergo a photomediated one-atom ring contraction that extrudes a heteroatom from the cyclic core. However, for nitrogenous heterocycles, this powerful skeletal edit has been limited to substrates bearing electron-withdrawing substituents on nitrogen. Moreover, the mechanism and wavelength-dependent efficiency of this transformation have remained unclear. In our most recent joint work between organic chemistry and photochemistry, we increased the electron richness of nitrogen in saturated azacycles to improve light absorption and strengthen critical intramolecular hydrogen bonding while enabling the direct installation of the photoreactive handle. As a result, a broadly expanded substrate scope, including underexplored electron-rich substrates and previously unsuccessful heterocycles, has now been achieved. The significantly improved yields and diastereoselectivities have facilitated reaction rate, kinetic isotope effect (KIE), and quenching studies, in addition to the determination of quantum yields. Guided by these studies, we propose a revised ET/PT mechanism for the ring contraction, which is additionally corroborated by computational characterization of the lowest-energy excited states of α-acylated substrates through time-dependent DFT. The efficiency of the ring contraction at wavelengths longer than those strongly absorbed by the substrates was investigated through wavelength-dependent rate measurements, which revealed a red shift of the photochemical action plot relative to substrate absorbance. The elucidated mechanistic and photophysical details effectively rationalize empirical observations, including additive effects, that were previously poorly understood. Our findings not only demonstrate enhanced synthetic utility of the photomediated ring contraction and shed light on mechanistic details but may also offer valuable guidance for understanding wavelength-dependent reactivity for related photochemical systems.
This research not only advances the synthetic utility of photomediated ring contraction but also sheds light on the mechanistic and photophysical aspects of photochemical systems. This work was jointly done between the Sarpong group, colleagues from Merck and Abbvie, and our group.
Published manuscript in the Journal of the American Chemical Society:
Topological defects play a key role in nonequilibrium phase transitions, ranging from birth of the early universe to quantum critical behavior of ultracold atoms. In solids, transient defects are known to generate a variety of hidden orders not accessible in equilibrium, but how defects are formed at the nanometer length scale and femtosecond timescale remains unknown. In this work, we discovered the sub-picosecond formation of 1D topological defects in a two-dimensional charge density wave using ultrafast electron diffraction. We discovered a dual-stage growth of 1D domain walls which takes place within 1 ps which is mediated by nonthermal lattice vibrations. This work constitutes the first visualization of topological defect formation process in the femtosecond timescale. Our work provides a framework for ultrafast engineering of topological defects based on selective excitation of collective modes, opening new avenues for dynamical control of nonequilibrium phases in correlated materials.
This work was done in collaboration with researchers from Shanghai Jiao Tong University, Brookhaven National Laboratory, ShanghaiTech University, University of Amsterdam and UCLA.
Press release by the College of Chemistry:
The paper is now published at Nature Physics:
An associated News & Views Article has been published by Isabella Gierz:
Open Access pre-print available here:
Today the workshop report of the Basic Research Needs (BRN) Workshop on Laser Technology was released. This workshop was co-organized by DOE, DOD and NSF, and held in Fall 2023. Michael contributed as scientific panel member to the workshop discussing needs for advanced laser technologies in ultrafast science. The full report can be read here: