Single-Crystal-to-Single-Crystal Radical-Ion Chain Reactions under the Electron Microscope: A Chemical Design to Repurpose Electron Beam Damage

Crystals designed to undergo electron beam-induced single-crystal-to-single-crystal (SC–SC) reactions were used for structural elucidation by microelectron diffraction (3D ED) and the results compared with those from crystals where the same reaction was expected to disrupt the crystal lattice. We confirmed that microcrystals of rctt-tetrakis(4-pyridyl)cyclobutane with 2,4-dichlororesorcinol (bpeD·dcr) or 2,4,6-trichlorophenol (bpeD·tcp) formed by supramolecular templating underwent smooth SC–SC cyclobutane splitting reactions to form trans-4,4′-bipyridylethene (bpe) in their corresponding crystalline complexes bpeD·dcr and bpeD·tcp. We also showed that the reactions are initiated by sporadic electron beam ionization events that are propagated by subsequent electron transfer steps. Electron beam damage was greatly mitigated, and the crystal structures could be solved in various steps of the reaction and through completion. By contrast, nontemplated crystals of rctt-tetrakis(4-pyridyl)cyclobutane complexed with iso-coumarin carboxylic acid (bpeD·icCA) and crystals of pure bpe underwent sluggish, non-SC–SC reactions, and displayed diffraction patterns that decayed more rapidly. These results suggest that structural damage caused by ionization-induced chemical changes may play a significant role in crystal decay for samples exposed to the high-energy beam of an electron microscope.