Sum-frequency generation (SFG) vibrational spectroscopy is employed to investigate the reversible, photoinduced trans/cis isomerization of an azobenzene-functionalized self-assembled monolayer (SAM) on a gold substrate. A C[triple bond]N marker group at the outer phenyl ring is used as a direct measure of the switching state. The azobenzene unit is connected to the surface by a tripodal linker system with an adamantane core, which results in both a sufficient decoupling of the functional azobenzene unit from the metallic substrate and a free volume to prevent steric hindrance, thus allowing the isomerization process. Optical excitation at 405 nm induces the trans-->cis isomerization, whereas light exposure at 470 nm leads to the back reaction. The effective cross sections for the reactions are sigma(eff)(cis) = 4 +/- 1 x 10(-18) cm(2) at 405 nm (trans-->cis) and sigma(eff)(trans) = 2.5 +/- 0.9 x 10(-19) cm(2) at 470 nm (cis-->trans). We propose that the photoisomerization is driven by a direct (intramolecular) electronic excitation of the azobenzene conjugate, analogous to the free molecules in solution.

The synthesis and aggregation behavior of photo-switchable, nonionic dendritic amphiphiles was investigated with regard to transport and release of guest molecules. The correlation between the critical micelle concentration and the switching ability is shown.

The synthesis, supramolecular complexation, and switching of new bifunctional azobenzene-oligoglycerol conjugates in different environments is reported. Through the formation of host-guest complexes with surface immobilized β-cyclodextrin receptors, the bifunctional switches were coupled to gold surfaces. The isomerization of the amphiphilic azobenzene derivatives was examined in solution, on gold nanoparticles, and on planar gold surfaces. The wettability of functionalized gold surfaces can be reversibly switched under light-illumination with two different wavelengths. Besides the photoisomerization processes and concomitant effects on functionality, the thermal cis to trans isomerization of the conjugates and their complexes was monitored. Thermal half-lives of the cis isomers were calculated for different environments. Surprisingly, the half-lives on gold nanoparticles were significantly smaller compared to planar gold surfaces.

Stimulus responsive surfactants based on dendritic glycerol azobenzene conjugates were used to solubilize and debundle single-walled carbon nanotubes in aqueous media. Their debundling property as well as their reaggregation behavior upon irradiation with light was examined and light triggered reversible bundling and precipitation are shown.

Wir berichten über die Synthese, die Komplexierung und das Schalten in verschiedenen Umgebungen neuer difunktionaler Azobenzol-Oligoglycerin-Konjugate. Zunächst wurden die Schalter durch Wirt-Gast-Chemie an Goldoberflächen gekuppelt, und zwar über b-Cyclodextrin-Rezeptoren, die zuvor auf den entsprechenden Oberflächen immobilisiert worden waren, sowie eine Adamantylgruppe am Azobenzol. Das Isomerisierungsverhalten der amphiphilen Azobenzolderivate wurde in Lçsung, auf Goldnanopartikeln und auf planaren Goldoberflächen untersucht. Durch die Bestrahlung mit Licht zweier Wellenlängen konnte die Benetzbarkeit der supramolekular funktionalisierten Oberflächen reversibel verändert werden. Zusätzlich zu den Photoisomerisierungsprozessen und den damit verbundenen Auswirkungen auf die Oberflächenfunktionalität wurde das thermische Rückschalten der cis-Isomere und ihrer Komplexe zur trans-Konfiguration beobachtet. So konnten thermische Halbwertszeiten der cis-Isomere errechnet werden, um eine Aussage über ihre Stabilität treffen zu kçnnen. Angewandte Chemie 9825