Complete suppression of fluorescence from a 9,10-bis(phenylethynyl)anthracene-based ring upon [2]catenane formation

Abstract We report the synthesis and characterization of a [2]catenane consisting of one fluorescent ring incorporating a 9,10-bis(phenylethynyl)anthracene and the other ring containing 2 naphthalene diimides as quenchers. The catenane was constructed via a modified Huisgen 1,3-dipolar cycloaddition between terminal alkyne and azide groups, introduced into precursors of the quencher ring in the presence of the fluorescent ring. In chloroform, the absorption spectra of the catenane showed a broad band between 500 and 700 nm, attributed to charge-transfer interactions between the fluorophore and quenchers. Titration experiments using a quencher ring and linear model compounds of the fluorescent ring suggested that the fluorophore in [2]catenane is sandwiched between the 2 quenchers. This configuration led to substantial shifts in the ¹H NMR signals of the fluorophore, compared to the free 9,10-bis(phenylethynyl)anthracene of the ring before catenane formation. While the fluorescent ring exhibited a high fluorescence quantum yield (Φ = 0.91), this was completely quenched upon catenane formation (Φ < 0.01). This pronounced fluorescence quenching makes the system a promising candidate for the development of supramolecular mechanophores capable of on/off fluorescence switching in response to applied force.