A fluorescent and photoresponsive host based on rigid polyphenylene dendrimers (PPDs) has been synthesized. The key building block for the divergent dendrimer buildup is a complex tetracyclone 12 containing azobenzenyl, pyridyl, and ethynyl entities. The rigidity of polyphenylenes is of crucial importance for a site-specific placement of different functions: eight azobenzene (AB) moieties into the rigid scaffold, a fluorescent perylenetetracarboxdiimide (PDI) into the core, and eight pyridin functions into the interior cavities. AB moieties of host-1 undergo reversible cis-trans photoisomerization and are photostable, as confirmed by various techniques: UV-vis, (1)H NMR, size exclusion chromatography, and fluorescence correlation (FCS). In this system, AB moieties act as photoswitchable hinges and enable control over (i) molecular size, (ii) intramolecular energy transfer between AB and PDI, and (iii) encapsulation and release of guest molecules. The presence of PDI allows not only following the effect of cis-trans photoisomerization on molecular size with highly sensitive FCS but also monitoring the efficiency of the intramolecular energy transfer process (from AB to PDI) by time-resolved optical spectroscopy. Pyridyl functions were incorporated to facilitate guest uptake via hydrogen bonds between the host and guests. Also, we have demonstrated that the photoswitchability of the host can be utilized to actively encapsulate guest molecules into its interior cavities. This novel, light-driven encapsulation mechanism could enable the design of new drug delivery systems.

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Auf die Größe kommt es an: Durch die Strategie der divergenten Dendronisierung können beispiellos große, formtreue und sperrige Anionen synthetisiert werden (siehe Bild). Ihre Größe, Dichte und die chemische Beschaffenheit der Oberfläche lassen sich maßschneidern, um hydrophobere, weniger nucleophile und schwächer koordinierende Anionen zu erhalten.

Light switch: a dendronized salt exhibiting photoswitchable conductivity was designed and synthesized. The salt consists of tetrabutylammonium cations and large, rigidly dendronized borate anions, each bearing eight photoresponsive azobenzene moieties. The conductivity of solutions of this salt can be reversibly switched by irradiation, owing to light-induced changes in the overall size of the dendronized anion and the density of its polyphenylene shell.