Side-chain functionalized luminescent polymers for organic light-emitting diode applications
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This thesis aims to provide a detailed understanding of side-chain functionalized polymers as emissive materials for OLEDs. The syntheses and photophysical properties of these solution-processable materials as well as the effects of metal types, polymer backbones, chain lengths, spacer types and lengths, host types, and concentrations of the metal complexes on the emission properties and device performance will be dicussed. The polymers were functionalized with host materials along with the metal complexes to enhance the charge transport and to obtain energy transfer from the host to the complex. The physical and photophysical properties of the polymers were tuned by changing the backbone and the metal complex. Poly(norbornene)s, poly(cyclooctene)s, and poly(styrene)s were studied. The differences in the glass transition temperatures and PDIs of the polymers indicated that device performances might be affected by the polymer type due to the differences in the processability of the polymers. In addition to the backbone, it was found that device performance is dependent on various parameters such as molecular weight, metal loading, spacer type, and spacer length. In each case, it was found that the polymer backbone does not interfere with the basic photopysical properties of the metal complexes. The two main classes of metal complexes studied in this thesis are metalloquinolates and iridium complexes. It was shown that the emission properties of poly(cyclooctene)s containing 8-hydroxyquinolines in their side-chains could be altered by simply changing the metal. Green- and near IR-emitting polymers were synthesized by employing aluminum and ytterbium, respectively. On the other hand, for the iridium complexes, changes in color were achieved by varying the ligands. Iridium containing polymers with emission spectra that span the entire visible spectrum were synthesized by employing the appropriate ligands. It was demonstrated that OLEDs with high efficiencies can be fabricated by using these polymers as the emissive layer.