Date

2021-11-26

Author

Çakal, Deniz

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Conjugated organic materials comprise a major field of material chemistry focused on the improvement of new building blocks for the synthesis of novel semiconducting materials with advanced functional properties. Such semiconducting systems have the advantage of low cost, solution processability and flexibility and find many applications in the field of plastic photovoltaics, electrochromics and display technologies. The electronic and optical features of these semiconducting organic materials can be tailored via molecular engineering. One of the most effective strategy for engineering at molecular level is utilizing donor-acceptor approach. This approach uses electron rich and electron deficient units to provide highly conductive and low band gap materials. Thiophene and its alkylenedioxythiophene derivatives are popular electron rich building blocks to construct donor units for conjugated semiconducting materials. Phthalimide (PI) and thieno[3,4-c]pyrrole-4,6-dione (TPD) compounds comprise two different classes of acceptor units having electron-withdrawing carbonyl groups. The pairing of thiophene based donors with PI and TPD acceptor units in donor-acceptor-donor configuration generates a series of conjugated monomers with a reduced energy gap to be investigated in this thesis from different perspectives. The first part of the thesis is dedicated to the modification of the electron deficient PI acceptor unit with two different side groups including polyhedral oligomeric silsesquioxane (POSS) and propyl functions and then the coupling of these novel PI acceptors with thiophene and 3,4-ethylenedioxythiophene (EDOT) donor units to obtain donor-acceptor-donor type monomers and their corresponding polymers. The final effort is dedicated to the investigation of the monomers and polymer within the donor-acceptor-donor configuration to provide an improved understanding of substituent and donor effect on optical and electronic properties of these conjugated materials. The second part of the thesis focused on the modification of TPD unit through functionalization with four different side groups involving ethylhexyl, POSS, azobenzene and fluoerene. Three of these side groups were appended into TPD acceptor unit for the first time. These functionalized TPD acceptor units were combined with thiophene, EDOT and highly soluble didecyl-substituted 3,4-propylenedioxythiophene (ProDOT) donor units to construct donor-acceptor-donor type conjugated organic frameworks. The investigation of these conjugated systems in donor-acceptor-donor configuration has provided a deep insight on evaluating the role of different types of functional side groups on the acceptor unit. Furthermore, optoelectronic features of these systems were investigated to elucidate the effect of aforementioned functional side groups as well as donor units. Lastly, these TPD-based donor-acceptor-donor architectures were compared with the previously synthesized PI-based analogs to unveil the effect of the acceptor group on optoelectronic properties. In the third and last part of the thesis, the formation of a new core unit was achieved by modifying PI acceptor unit within donor-acceptor-donor configuration. This modification is achieved by converting imide functional group of the acceptor moiety into diimide. The obtained novel system was further investigated to shed light on the structural effects of both diimide functional group and benzene ring structure on the acceptor units. The chemiluminescence characteristics of the newly synthesized system was also investigated as well as its optoelectronic properties. The optoelectronic data obtained for the trimeric system with the modified core unit was reported together with the unmodified ones for comparision sake and all the results were also supported by computational calculations. In this dissertation, it was found that donor and acceptor units play key roles on the electrochemical and optical behaviors such as band gap, neutral state color, and electrochromic performance while the substituent does not significantly change optoelectronic properties of polymers. Also, the effect of donor units on the electrochemical and optical band gap values of polymers were investigated, it was found that each series follow the same trend depending on the strength of donor unit (i.e. Eg,Thiophene > Eg,ProDOT > Eg,EDOT ). A similar trend was also detected for the oxidation potentials of the monomers. When the effect of acceptor units on the optoelectronic properties were investigated, it was found that more improved results were observed for TPD-based polymers as compared to PI-based polymer. This study also shows that the acceptor such as PI and TPD can be modified by any functional group to impart new functionalities without altering their optoelectronic properties.

Subject Keywords

Donor-Acceptor-Donor Type Monomers, Phthalimide and Thieno[3,4-c]pyrrole-4,6-dione Acceptors, New Substituents on Acceptors (POSS, Azobenzene, Fluorene), Chemiluminescence

URI

https://hdl.handle.net/11511/95109

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Graduate School of Natural and Applied Sciences, Thesis