Ketone defects

L. Romaner, G. Heimel, H. Weisenhofer, P.S. de Freitas, U. Scherf, J.-L. Bredas, E. Zojer, and E.J.W. List, Ketonic defects in ladder-type poly(p-phenylene)s, Chem. Mater., 16 4667-4674, 2004. 

Scheme 15 Mono- and dialkylated polyfluorenes used to test the ketone defect hypothesis...

Scheme 16 Proposed mechanism for formation of ketone defects 39...

Other approaches have involved reduction of interchain interaction either by cross-linking the polymers using vinyl endgroups [ 71 ] or by attaching bulky groups, e.g., dendrimers [72,73] or silsesquioxanes [74,75], as end- or side-groups. There is evidence that reduction of fluorene by calcium cathodes is implicated in the formation of ketone defects during LED operation, and this can be suppressed by introduction of a buffer layer between the polymer and the cathode [76]. 

Ketonic Defects Related to Polymer Synthesis Oxidative Degradation of PF-Type Polymers Spectral Degradation of PPP-Based Light-Emitting Devices... 

Wiesenhofer H, Beljonne D, Scholes GD, Hennebicq E, Bredas JL, Zojer E (2005) Limitations of the Forster destaiption of singlet exciton migration the illustrative example of energy transfer to ketonic defects in ladder-type poly(para-phenylenes). Adv Funct Mater 15 155... 

Fig. 20. Generation of a ketone defect by nus-addition of the growing cluun...

The same kind of ketone defect is also introduced thermally at 150 by an autoxidation proces involving attack at the backbone methylene group. 

---