A team of French chemists have shown how two different polymers can be made to interact to produce a fluorescent hybrid.

Dynamic polymers are different from normal polymers in that the bonds that hold the monomers together can break and re-form. Jean-Marie Lehn and colleagues at the Université Louis Pasteur in Strasbourg, France, have now used this phenomenon to make a layered polymer hybrid that fluoresces when heated.

The principle consists of layering two different dynamic polymers, and then heating them so that bond exchange takes place. This changes the properties of the boundary region, in this case leading to fluorescence, which has potential for implementation in optical materials, said Lehn.

The key to developing these polymers was the nature of the monomers used to make them. The team first made a monomer consisting of a central unit flanked by two polyether chains, each linked to the central unit by a reversible N=C bond. They then made a similar monomer with slightly different central and flanking groups. These monomers were then converted to their respective polymers, both of which were nearly colourless. To show the fluorescence phenomenon in action, Lehn and colleagues overlapped a thin film of each polymer and heated them briefly to about 160 °C. This caused some of the N=C bonds in the overlapped section to break and re-combine with the other polymer, producing a polymer hybrid at the interface.

Under UV light, the hybrid produced a yellow-green fluorescence, caused by the different arrangement of double bonds. This feature, said Lehn, shows how polymers can be controlled by and respond to external stimuli. It also illustrates their potential in molecular sensing and photoactive devices, and gives, he said, 'a sort of Darwinian flavour to chemistry!' 

David Barden