Design and Synthesis of Novel Photoswitches for the Platform Concept
Within this thesis three different photoswitchable units were designed and investigated to achieve a unidirectional movement on the surface. Both the lateral movement of the adsorbed molecules about the surface and the transport of nanoparticles was the goal of this work. Thus, particularly suited photoswitchable molecules were designed towards this end. To achieve a lateral movement of the molecules on the surface an azobenzene moiety was spanned between two TATA platforms parallel to the surface. Two different molecules were synthesized which could both be switched to high percentage (>95 %) to the corresponding cis configuration and several switching cycles show no fatigue or decay. For the realization of an artificial ciliated epithelium an imine-functionalized monolayer on a Au(111) surface was developed. Therefore, six imine-functionalized TATA platforms were synthesized and their photochemical properties were investigated in solution. The cis isomers could be accumulated upon irradiation with 365 nm up to 50 %, which was verified by low temperature 1H NMR and UV/vis spectroscopy (215-233 K). Rate constants for the back isomerization were determined for several temperatures and hence, the half-life at room temperature could be extrapolated as t1/2= 0.58 s. The formation of highly ordered monolayers was confirmed by scanning tunneling microscopy and UV/vis measurements of these surfaces showed the integrity of the photoswitchable unit. Futhermore, the synthesis of a new class of photoswitches was realized. These heterodiazocines exhibit outstanding photochemical properties whereas the synthesis is simplified with respect to the parent diazocines. Hence, a new approach for the synthesis of unsymmetric diazocines was developed. Moreover, these diazocines can be efficiently switched with light in the near infrared region which opens up applications as in vivo photoswitchable drugs and functional materials.
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