| dc.description.abstract | A class of materials known as conjugated polymers (CPs) has been shown to integrate the physical properties of organic plastics such as low-weight, flexibility, and synthetic modularity with electronic semiconducting properties typically found in inorganic materials. While a variety of parameters determine the resultant material’s conductivity, a crucial factor is the bandgap (Eg). Specifically, thieno[3,4-b]pyrazine (TP) has found success in generating low Eg CPs (i.e. Eg < 1.5 eV), largely in part due to its ambipolar identity. Two strategies to achieve Eg values < 1 eV include extending the conjugation of TP through ring fusion and pairing TP with strong electron accepting moieties. The investigation into extended ring TPs as low bandgap homopolymers was initially pursued with the synthesis of poly(acenaphtho[1,2-b]thieno[3,4-e]pyrazine), a record setting low Eg homopolymer. Upon this realization of driving Eg¬ values down through ring fusion on the pyrazine portion of TP, additional analogues were considered with 2λ4δ2-dithieno[3,4-b:3’,4’-e]pyrazine as one of the most promising candidates due to its predicted Eg of 0.14 eV. Efforts into this research have produced a variety of precursors and analogues, adding to the family of TPs for further study.
A second strategy for Eg reduction is through the pairing of electronically mismatched units known as donors and acceptors. While this does reduce Eg, the underlying principles of the cause is disputed. Thus, to further understand the interactions in these types of copolymer systems, a small molecule study was designed with a strong donor, a strong acceptor, and the ambipolar unit TP in which six possible dimer configurations were synthesized and analyzed to determine the extent of donor-acceptor interactions. Lastly, an investigation into TP-acceptor alternating copolymers was carried out by pairing TP with two acceptors of varying accepting strength and contributions to polymer solubility. Because of the atypical design of these copolymers, a relatively new cross-coupling method known as direct arylation polymerization was used in their synthesis. The optimization of which produced a CP with an Eg of 0.93 eV. These results thus provide evidence for a new design motif for low bandgap CPs that further refines our understanding of donor-acceptor relationships. | en_US |
