Researchers have discovered families of stable blue-light emitting materials that could overcome a longstanding drawback of polymer light-emitting diodes (PLEDs). 

The problem is that in full-colour PLED displays (consisting of red, green and blue-emitting pixels), the blue pixels have a relatively limited lifespan.   

Two independent teams - one based at the University of Cambridge, UK; the other a collaboration between Donetsk University, Ukraine, and the University of Durham, UK - have produced stable variants of the blue-light emitting industry standard - poly(9,9-di-octyl)fluorene (PF). 

Essentially, the carbon atom at the PF monomer's 9-position is replaced with a substituted second-row element. The Cambridge team made 2,7-dibenzosilole and then polymerised it ( A );¹ the Durham-Donetsk team replaced the carbon at PF's 9-position with SO₂ to prepare dibenzothiophene-S,S-dioxide, which was then formed into co-oligomers with 9,9-dihexylfluorene.  ( B )² 

'Our approach is similar to the Cambridge group's in that we both needed to lower the energy of the semiconductor-like bands in the polymer,' said Martin Bryce at the University of Durham, who coordinated the Durham-Donetsk group. 'This would improve PF's electron transporting properties and stop it degrading. Both our approaches achieve this: the Cambridge group's enhanced colour stability of their new polymer over PF is impressive'. 

Andrew Holmes, who led the Cambridge group, agrees: 'Our approach completely avoids this problem of ketone formation by being a better electron acceptor than PF.   

'Our new polymer is also thermally stable and shows good blue-light emission in a PLED device. I am delighted by the excellent work of Martin Bryce's Durham-Donetsk collaboration, which achieves the same goal with its co-oligomers - a stable blue-light emitting polymer,' he said. 
Lionel Milgrom