The electrochemical and optical investigation of the impacts of structural alterations on the conjugated polymers’ backbone and side chain

Date

2024-7-31

Author

Demir Arabacı, Elif

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The donor-acceptor technique is a highly effective strategy for molecular engineering at the molecular level. This method utilizes components with electron-rich and deficient units to produce materials that have both high conductivity and a narrow Eg. In this thesis, alkylenedioxythiophene derivatives and benzo[1,2-b:4,5-b']dithiophene (BDT), were employed as donor units, and fluorene, silafluorene, thieno[3,4-c]pyrrole-4,6-dione (TPD), and benzooxadiazole (BOz) were employed as acceptor units. In the first part of this thesis, the main purpose is to investigate the impact of the bridging C-9 atom (fluorene vs. silafluorene) of the fused ring system and the effect of different donor units. Examining the optoelectronic properties of polymers reveals that silafluorene-based polymers have lower Eox and Eg values compared to their fluorene-based counterparts. The reason for this is the enhanced planarity and conjugation that occur when a less electronegative silicon (Si) atom is included into the fused ring structure. Additionally, it was observed that EDOT-containing analogs have Eg values that are approximately 0.3 eV lower than ProDOT-containing analogs. The second part of this thesis investigates the effect of the side chain (branched-ethylhexyl vs. linear-octyl) on the imide nitrogen of the TPD acceptor unit, as well as the effect of donor strength. Changing alkyl chains at the imide nitrogen of the TPD causes no obvious change in the optoelectronic properties of the polymers, which is ascribed to the loss of conjugation between the TPD-core unit and the alkyl chain. The results also indicate that EDOT-containing polymers have lower Eox and Eg levels than ProDOT-containing analogs. This can be attributed to the twist structure of ProDOT, which reduces the overlap between the oxygen lone pairs and the aromatic thiophene ring. In the third part of the thesis, the main purpose is the investigation of the impact of these bridge units on their optical and electrochemical characteristics, and on the photochemical stability of polymers. All polymers consist of the same donor (BDT) and acceptor (BOz) units but different π-bridges, like thiophene, selenophene, and thiazole. The optoelectronic properties of polymers show that the polymer film with selenophene π-bridge exhibit the lowest Eg, followed by thiophene and thiazole. A reverse correlation was observed between the bandgap and photostability of conjugated polymers. The polymer film with thiazole bridge exhibits the highest Eg value and demonstrates the greatest resistance to photooxidation.

Subject Keywords

Donor-Acceptor Approach, Electrochromism, Photostability, Bridging Atom Effect, Side Chain Effect, π-bridge effect

URI

https://hdl.handle.net/11511/110855

Collections

Graduate School of Natural and Applied Sciences, Thesis