Controlling the twist of a polymer backbone has enabled US chemists to tune the polymer's optical and electronic properties. 

John Reynolds and colleagues at the University of Florida, took poly(3,4-propylenedioxythiophene) (ProDOT), and connected its monomers together into small loops. Usually polymers are made of a string of monomers that can rotate freely. Adding extra tethers between monomers holds them in place and reduces their freedom to move, said Reynolds. 

The modified ProDOT polymer is electrically switchable. In its oxidised form it is colourless, but when reduced it turns orange. 

The team reports that the angle between monomers in the modified ProDOT polymer is 30 degrees, compared with 180 degrees in the unaltered polymer. Reynolds said that changing the length of the connecting tether will allow control over the polymer's properties, and he is currently working on making polymers with different lengths of tether. 'We believe that the polymer torsion angle can be 'dialled in' by modifying the length and composition of the tether,' Reynolds said. 

This study provides chemists with another way of controlling the emission and energy levels of polymers so that they can be optimised for use in LEDs and solar cells, said Reynolds. 

The team's goal is to scale up the synthesis so that the polymers can be made in large enough batches for device fabrication.  

Clare E Boothby