3 years ago

Forbidden Chemistry: Two-Photon Pathway in [2+2] Cycloaddition of Maleimides

Forbidden Chemistry: Two-Photon Pathway in [2+2] Cycloaddition of Maleimides
Carsten Werner, Christiane Jungnickel, Michael Schlierf, Mikhail V. Tsurkan
Two-photon excitation provides high spatial resolution in three dimensions of the corresponding chemical or physical processes, allowing submicrometer structuring in stereolithography and three-dimensional (3D) microfabrication. While studying two-photon structuring applications, we observed an undescribed phenomenon in photochemistry that dictates reactivity of maleimide groups in two-photon mode. A low-absorbance transition formerly ignored in classical photochemistry has been found for maleimides. This transition was assigned to symmetry-breaking donor–acceptor complex formation, which revealed a formally forbidden pathway in [2+2] cycloaddition reactions of maleimide moieties. This synthetic pathway allowed for the creation of hydrogel materials under physiological conditions at low laser excitation energy (0.1 J/cm2 at 800 nm) without the use of photoinitiators, which makes it truly two-photon click chemistry.

Publisher URL: http://dx.doi.org/10.1021/jacs.7b04484

DOI: 10.1021/jacs.7b04484

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