Issue 9, 2007

Control of luminescence in conjugated polymers through control of chain microstructure

Abstract

The development of semiconducting polymers with high solid-state luminescence efficiencies has enabled the fabrication of efficient polymer light-emitting diodes. Luminescence is often quenched in well-ordered molecular solids, as a result of inter-molecular dipolar coupling, and the general observation of efficient luminescence in semiconducting polymers is unexpected. We report here the synthesis and characterisation of a series of model ‘glassy’ poly(arylenevinylene)s where we control the cis to trans ratio about the vinylene linkage and also the phenylene linkage geometry. Photoluminescence efficiency is enhanced for more disordered materials, with highest values for 50 : 50 cis : trans ratios, when it exceeds 50%. We also find that the free volume associated with these glassy disordered polymers allows conformational relaxation of the excitonic state, via ring rotation at the vinylene linkage, causing a large Stokes' shift of the emission. We propose that high luminescence efficiency in these glassy polymers is due to emission from the more disordered regions, and that two effects due to disorder are simultaneously required: firstly that these regions are luminescent (prevention of aggregation by disorder), and, secondly, that the electronic excited state (exciton) can lower its energy below its value in more ordered regions by means of the ring-rotational coupling.

Graphical abstract: Control of luminescence in conjugated polymers through control of chain microstructure

Article information

Article type
Paper
Submitted
23 Oct 2006
Accepted
27 Nov 2006
First published
12 Dec 2006

J. Mater. Chem., 2007,17, 907-912

Control of luminescence in conjugated polymers through control of chain microstructure

W. J. Feast, F. Cacialli, A. T. H. Koch, R. Daik, C. Lartigau, R. H. Friend, D. Beljonne and J. Brédas, J. Mater. Chem., 2007, 17, 907 DOI: 10.1039/B615408P

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