Interactions With and Among the Azobenzene Scaffold in Photoswitches

Abstract

Azobenzenes, with their ability to undergo a reversible change from the (E)- to the (Z)-isomer by irradiation with light, have a wide range of possibilities in various fields of research, including host-guest chemistry, information- or energy storage. To successfully incorporate azobenzenes in the previously mentioned applications it is essential to have a thorough understanding of the effects of the interactions with or among the azobenzene scaffold. Apart from the interactions of azobenzenes with sensitizers, catalysts or solvent molecules, intramolecular interactions also significantly influence their isomerization behavior. For the latter, the role of substituents and their pattern is crucial, as they can influence the electronics and thermodynamics of those systems. In this context, the stabilizing effects of London dispersion forces on different non-symmetric azobenzenes were examined. The strategic introduction of meta-alkyl substituents on one phenyl ring and electron rich or poor meta-aryl moieties on the other phenyl unit revealed the decisive factor for the observed stabilization among the azobenzene scaffold. The addition of one or more photoswitchable units to the azobenzene scaffold as substituent(s), provides multiphotochromic systems with expected increased information and storage density. Nonetheless, complex mixtures can arise, wherein their interplay is still not fully understood. Therefore, the interaction of different photochromic systems with the azobenzene scaffold, including the interaction of combined azobenzenes in close proximity, was investigated in this work. Lastly, the synthesis of azobenzenes was improved by applying the prominent Baeyer-Mills coupling reaction to a continuous flow system. This led to an efficient, reproducible and large scale approach which is essential for future applications of this fascinating compound class.