Tetra-TTF Calix[4]pyrrole: A Rationally Designed Receptor for Electron-Deficient Neutral Guests

A calix[4]pyrrole incorporating four appended tetrathiafulvalene (TTF) units has been synthesized, and its receptor abilities toward neutral electron-deficient guests, such as 1,3,5-trinitrobenzene, tetrafluoro-p-benzoquinone, and tetrachloro-p-benzoquinone, have been studied in solution by UV−vis and 1H NMR spectroscopies as well as in the solid-state by X-ray crystallography. In its 1,3-alternate conformation a 1:2 sandwich-like complexstabilized by charge transfer and hydrogen bonding interactionsis formed between the tetra-TTF calix[4]pyrrole and the guest molecules. However, upon addition of chloride ions to the complex the 1,3-alternate conformation is changed in favor of a cone conformation which serves to effect a release of the guests from the tetra-TTF calix[4]pyrrole.