Perylene diimide-based materials for organic electronics and optical limiting applications
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This thesis described the synthesis and characterization of new perylene diimide (PDI)-based photonic and electronic materials. In the first part of this thesis, PDI-based polynorbornenes, including PDI-grafted homopolymers and block-copolymers (BCPs) were synthesized and characterized as alternative acceptors for fullerenes for organic electronics. It was found that the PDIs on the polymer side-chains affect π-π stacking with the neighboring PDIs, which has implications for the use of these materials for organic field-effect transistors (OFETs) and organic photovoltaic devices (OPVs). It should be noted that the performance of solar cell based on these materials was poor, like other similar materials. The major reasons could be the challenge in controlling the molecular alignment of the PDI-based materials, which leads to lower electron mobilities in films compared to devices with fullerene-based acceptors. One PDI-grafted BCP showed better OPV performance compared to the other BCPs and respective homepolymer blends, presumably due to favorable morphology. In the second part of this thesis, photo-induced charge-separation in blends of poly-3-hexyl-thiophene (P3HT) and various PDI derivatives have been studied. Probing of long-lived photo-generated PDI radical anions provided insight on these photo-induced processes and their use for OPVs. In the third part of this thesis, the use of photo-generated PDI radical-anion absorption was shown to be effective for optical limiting of nanosecond laser pulses between 650 - 800 nm. In Chapter 5, an effective approach for two-photon absorption (2PA)-induced optical limiting using donor-PDI dyads through which donors and acceptors can be independently chosen to maximize optical suppression at particular wavelengths has been demonstrated. In Chapter 6, conjugated polymers with PDI pendants and poly(carbazole-alt-2,7-fluorene) main-chains were synthesized for optical limiting using the photo-generated PDI radical anion via PDI aggregate excitation and/or 2PA from the polymer backbones. It was also found that nitro-phenyl group or similar derivatives could be good candidates to incorporate into those donor-conjugated polymers, which have significant overlap between their 2PA band and respective polaron absorptions for 2PA-indced optical limiting.