Tetraphenylethylene Foldamers with Double Hairpin‐Turn Linkers, TNT‐Binding Mode and Detection of Highly Diluted TNT Vapor

Tetraphenylethylene (TPE) foldamers with double hairpin‐turn linkers showing an aggregation‐induced emission (AIE) effect have been synthesized for the first time. A crystal structure of a foldamer–TNT complex has been obtained, enabling unprecedented direct observation of the interactions between TNT molecules and the chromophores of the foldamer. Instead of π–π stacking interactions, which have often been considered to be the key mechanism in the binding of TNT by chromophoric receptors, strong n–π interactions between the nitro groups of TNT and the aromatic rings of the foldamer have been found. Exceptionally, by addition of 1 % NaF to a suspension of the foldamer in H2O/THF (95:5), the fluorescence quenching efficiency by TNT vapor significantly increased from about 20 % to more than 90 %. Even after diluting TNT‐saturated air at 25 °C by a factor of 2×104, an obvious quenching response was observed, indicating that ultratrace TNT vapor (down to 3.4 fg per mL of air) could be detected. A good nose: Novel tetraphenylethylene (TPE) foldamers with double hairpin‐turn linkers showing an aggregation‐induced emission (AIE) effect have been synthesized. Such a foldamer can form a complex with a molecule of the explosive TNT (see graphic), and the resulting AIE allows the detection of ultratrace TNT vapor at levels as low as 3.4 fg per mL of air.