Most Recent Publications
From Beam Damage to Massive Reaction Amplification under the Electron Microscope: An Ionization-Induced Chain Reaction in Crystals of a Dewar Benzene
Electron microscopy in its various forms is one of the most powerful imaging and structural elucidation methods in nanotechnology where sample information is generally limited by random chemical and structural damage. Here we show how a well-selected chemical probe can be used to transform indiscriminate chemical damage into clean chemical processes that can be used to characterize some aspects of the interactions between high-energy electron beams and soft organic matter. Crystals of a Dewar benzene exposed to a 300 keV electron beam facilitate a clean valence-bond isomerization radical-cation chain reaction where the number of chemical events per incident electron is amplified by a factor of up to ca. 90,000
Cascade Photoreaction in Crystals: A Phase Change Caused by a Dewar Benzene Quantum Chain Triggers a Topochemical [2 + 2] Photodimerization
Crystals undergoing tandem reactions where the first transformation enables the second one are rare. Using photoreactive Dewar benzene 3,4,5,6-tetramethyl-1,2-dicarboxylic diacid (DB) as a hydrogen-bonding template for the [2π+2π] photodimerization of trans-4,4′-bipyridyl-ethenes (BPE), we obtained crystals DB-BPE-NT with a DB:BPE = 2:1 stoichiometry with double bonds at a nonreactive distance of 5.957 Å. Exposure to UV light resulted in valence bond isomerization to Hückel benzene 3,4,5,6-tetramethyl-1,2-dicarboxylic acid (HB) by a quantum chain reaction that triggered the sought-after topochemical [2π+2π] photodimerization reaction. Notably, crystals HB:BPE-T with the Hückel benzene isomer and BPE adopted a 2:2 stoichiometry and displayed an efficient topochemically templated photodimerization reaction
Photoswitching Molecules Functionalized with Optical Cycling Centers Provide a Novel Platform for Studying Chemical Transformations in Ultracold Molecules
A novel molecular structure that bridges the fields of molecular optical cycling and molecular photoswitching is presented. It is based on a photoswitching molecule azobenzene functionalized with one and two CaO- groups, which can act as optical cycling centers (OCCs). This paper characterizes the electronic structure of the resulting model systems, focusing on three questions: (1) how the electronic states of the photoswitch are impacted by a functionalization with an OCC; (2) how the states of the OCC are impacted by the scaffold of the photoswitch; and (3) whether the OCC can serve as a spectroscopic probe of isomerization. The experimental feasibility of the proposed design and the advantages that organic synthesis can offer in the further functionalization of this molecular scaffold are also discussed. This work brings into the field of molecular optical cycling a new dimension of chemical complexity intrinsic to only polyatomic molecules
