A molecule shaped like a bow tie changes colour in the presence of toxic chemicals, which could make it useful for monitoring air

By Alice Klein
Looking smart
Huan Cong, Technical Institute of Physics and Chemistry, China
Chemists have constructed a bow tie-shaped molecule that changes colour under different conditions. It could be used to monitor toxic chemicals in air.
Huan Cong at the Technical Institute of Physics and Chemistry in China and his colleagues assembled the substance, which they call BowtieArene, by connecting two pentagon-shaped molecules called pillararenes. The two pillararenes were joined by a fluorescent molecule called tetraphenylethylene that formed the knot of the bow tie.
When they mixed individual bow tie molecules together, their electron interactions caused them to stack neatly on top of each other in a herringbone-like arrangement. The resulting orderly crystals interacted with light to produce blue fluorescence.
In contrast, when the researchers broke these ordered structures apart, either by mechanically grinding or scratching the crystals or dissolving them in liquid, the separated bow ties emitted green or yellow fluorescence.
Next, the team showed they could make the bow ties blue again by exposing them to the vapour of a chemical called xylene, which pulled the individual molecules back into an orderly arrangement.
This colour-switching property could be used to make sensors that detect toxic chemicals in the air or reveal when mechanical forces are present, says Cong. His team is currently designing different versions of the bow tie molecule to detect a range of different chemicals.
This isn’t the first time that chemists have made molecules with wacky shapes. They have also assembled molecules in the shape of churches, houses, Japanese pagodas, baskets, bird cages, and Olympic rings.
Journal reference: Angewandte Chemie International Edition, DOI: 10.1002/anie.201913340
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