Synthesis of a Hexagonal Nanosized Macrocyclic Fluorophore with Integrated Endotopic Terpyridine Metal-Chelation Sites

A rigid nanosized hexagonal phenylethynyl cyclophane 5 has been prepared, which incorporates two 2,2′:6′,2″‐terpyridines as integral structural units, for the purpose of binding metal ions. Macrocycle 5 was obtained by a 14‐step synthesis in an overall yield of 11 %, and was characterised by spectroscopic techniques. The efficiency and ease of all transformations, and the relatively enhanced yield of the final macrocyclisation suggests that the entire synthetic pathway should be amenable to scale‐up. Cyclophane 5 possesses four bulky triisopropylsilyl(TIPS)‐protected ethyne substituents which serve a dual role. Firstly, they solubilise the structure thereby facilitating purification and subsequent handling. Secondly, they enable post‐synthetic modification in which additional functionality may be attached to the periphery of the ring. Significantly, 5 was found to be a fluorescent chromophore, and may therefore potentially function as a new sensory platform for the detection of metal ions and H‐bond donating biological substrates. The structurally well‐defined nanosized morphology of 5, coupled with its interesting spectroscopic properties, supports the expectation that 5 and related architectures will attain a wealth of future applications within the developing fields of nanochemistry and nanoscience. Sterically encumbered bis(terpyridine) nanophane 1 has been successfully prepared using a synthesis which culminates in a surprisingly efficient macrocyclisation step. The triisopropylsilyl‐protected alkynes that help solubilise the structure should also allow post‐synthetic modification and modulation of its materials properties. Macrocycle 1 is also a strongly fluorescent chromophore, and may thus find many potential applications such as a new class of nanosized fluorescence sensors for biological substrates and metal ions.