Molecular platforms as versatile building blocks for multifunctional photoswitchable surfaces.

Controlled attachment of photoswitchable molecules to solid surfaces is a promising route for the realization of complex machine-like molecular functions. A central next step here is the preparation of adlayers with multiple chemical functions that have defined intermolecular spacings and orientations and interact with each other in a controlled way, resulting in novel advanced system properties. We demonstrate that this is possible using molecular platforms with vertical functional units. Employing molecular components with identical triazatriangulenium-based units, we prepared mixed adlayers of platforms carrying a stable photoswitch and bare platforms, platforms with vertical pyridine units, and platforms with metastable switches, respectively. All these mixed layers are highly hexagonally ordered, can be easily varied in composition, and exhibit a stochastic arrangement of the two molecular components.

Heterodiazocines: Synthesis and Photochromic Properties, Trans to Cis Switching within the Bio-optical Window.

Diazocines, bridged azobenzenes, exhibit superior photophysical properties compared to parent azobenzenes such as high switching efficiencies, quantum yields, and particularly switching wavelengths in the visible range. Synthesis, however, proceeds with low yields, and derivatives are difficult to prepare. We now present two heterodiazocines which are easier to synthesize, and the general procedures should also provide facile access to derivatives. Moreover, both compounds can be switched with light in the far-red (650 nm). Accessibility and photophysical properties make them ideal candidates for applications such as photoswitchable drugs and functional materials.

Imine-Functionalized Triazatriangulenium Platforms: Towards an Artificial Ciliated Epithelium.

Triazatriangulenium (TATA) platforms have been used to prepare highly ordered, self-assembled monolayers of free- and vertically standing imines on Au(111) surfaces. Upon irradiation, the imines undergo trans-cis isomerization and a fast thermal reaction (t1/2 =0.58 s at 20 °C) back to the more stable trans form. It is known that the photochemical reaction proceeds through rotation of the C=N bond and the thermochemical reaction through inversion at the N atom. The imine motors, therefore, should be able to induce a net displacement of particles above the surface similar to cilia epithelia in nature.

Laterally Mounted Azobenzenes on Platforms.

Triazatriangulenium ions have previously been used as platforms to prepare self-assembled monolayers of functional molecules such as azobenzenes with vertical orientation and that are free-standing on gold surfaces. We have now prepared azobenzenes that are spanned between two posts which are attached on two platforms. Absorbed on a gold surface, the azobenzene should be laterally oriented at a distance of more than 4 Å above and thus electronically decoupled from the surface, and the system should perform a muscle-type movement upon isomerization.