SUPER-RESOLUTION PHOTO “CLICK” CHEMISTRY
SUPER-RESOLUTION PHOTO “CLICK” CHEMISTRY

Summary/Abstract: The accessible resolution has changed significantly as a result of recent advancements in super-resolution microscopy, which have also significantly overcome the diffraction barrier. A reversible molecular switch serves as the fundamental component, enabling light-promoted activation and deactivation in conjunction with a laser focus that has a regular or tailor-shaped point spread function. Reversible Saturable Optically Linear Fluorescence Transitions RESOLFT microscopy is based on optically switching isomerization states and other optically bistable transitions in fluorophores. For this process, very low laser powers are sufficient for the “depletion” beam since optically triggered transitions of the marker molecule between the two isomeric states are orders of magnitude slower than the fluorescence lifetime. As a matter of fact, the diffraction barrier can be surpassed with considerably lower light intensity of the depletion beam in RESOLFT microscopy compared to STED microscopy. Recently, this concept has been carried from microscopy to optical lithography. Here we show a system that reaches such a molecular switch for “click” chemistry reactions such as the thiol-Michael addition. In particular, simultaneous irradiation at 532 nm can reversibly deplete the intermediate reversible photo-isomerization state of spirothiopyran (STP) produced by two photon absorption at 780 nm wavelength. This will suppress the subsequent thiol-Michael addition reaction, which forms the chemical basis of the "click" process of maleimide with the thiol. We demonstrate that this mechanism allows for stimulated emission depletion (STED) inspired reversible photoisomerization of STP in order to permit and prohibit the reaction down to the molecular level. STP itself is tested as a photoinitiator for super-resolution optical lithography. A crucial step of this work is the application of RESOLFT for supper resolution tailored chemical reactions, modifications and functionalization. In principle, SPT compounds also give promise as new photoinitiators in the toolbox of STED/RESOLFT optical lithography. The synthesized compounds were characterized using ¹H Nuclear Magnetic Resonance (¹H NMR), Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (AFM) to confirm their chemical structure, morphology, and surface topography.

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