Light emitting properties of fluorine-substituted poly(1,4-phenylene vinylenes)

Three fluorine-containing polymers, poly(2-fluoro-1,4-phenylene vinylene), poly(2,5-difluoro-1,4-phenylene vinylene), and poly(2[5]-(n-hexyloxy)-5[2]-fluoro-1,4-phenylene vinylene) (1-3, respectively) have been synthesized by the soluble precursor method and were used to fabricate light emitting diode (LED) devices. Monosubstituted 1 yielded an electroluminescent emission peaking at 560 nm (green-yellow; polymers 2 and 3 emitted in the 600-610 nm region (red). The result for 1 represents a blue shift in emission relative to emission from hompolymeric unsubstituted poly(1,4-phenylene vinylene) (PPV) LEDs fabricated by similar techniques, while the results for 2 and 3 represent a substantial red shift. These results may be compared to those obtained from LEDs fabricated from copolymers of PPV and poly(2,3,5,6-tetrafluoro-1,4-phenylene vinylene), which show a slightly blue shifted emission relative to homopolymeric PPV (Benjamin, I.; Faraggi, E. Z.; Avny, Y. Davidov, D.; Neumann, R. Chem. Mater. 1996, 8, 352). The qualitative difference in EL emission for this work compared to that of Benjamin ct al. is attributed to the fact that EL emission from 1-3 reflects the electronic effects of fluorine substitution upon the EL spectra, whereas the work of Benjamin ed al. demonstrated the effects of changes in the average chain length of EL emitting homo-PPV blocks in PPV-co-PPVF4 copolymers.