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    Photoinduced step-growth polymerizations of thiophene-carbazole based covalent organic polymer
    (Elsevier Sci Ltd, 2023) Celiker, Tugba; Altinisik, Sinem; Yagci, Yusuf; Koyuncu, Sermet
    A novel metal-free photochemical method for the synthesis of porous conjugated polymers was used to inves-tigate the effects of introducing thiophene co-monomer to the carbazole-based polymer, 4,4 '-bis(3,6-di(thiophen-2-yl)-9H-carbazol-9-yl)-1,1 '-biphenyl (CBP-Th), in terms of its structural, optical, electrochemical and morphological properties. Irradiation of a CBP-Th monomer solution led to the formation of a dark-colored polymer, PCBP-Th, and the role of thiophene on polymerization was investigated, involving electron transfer between CBP-Th and the iodonium ion in the exciplex produced by proton release and radical coupling reactions. The UV-Vis spectra broadened and redshifted due to the elongation of conjugation and solid-state pi-pi in-teractions by extra thiophene additive after the polymerization process. The addition of thiophene co-monomer also resulted in decreasing the onset potentials and thus slightly raised HOMO positions determined by the DPV technique. In theoretical calculations, it has been observed that the charge distribution of PCBP-Th at HOMO is over the entire conjugated structure and it has localization in thiophene-thiophene bridges at LUMO. Since the thiophene co-monomer changes the intermolecular distance, the thermal stability of PCBP-Th polymers de-creases and accordingly increases the amorphous characters. According to AFM, TEM and SEM images, intro-ducing the thiophene co-monomer led to the formation of larger clusters, resulting in a more pronounced surface texture on both the powders and thin films.
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    Polypyrenes by Photoinduced Step-Growth Polymerization
    (Amer Chemical Soc, 2020) Celiker, Tugba; Kaya, Kerem; Koyuncu, Sermet; Yagci, Yusuf
    Photoinduced processes have been widely utilized in macromolecular synthesis through radical, cationic, anionic, and controlled/living polymerizations and ligation processes. 'While widely utilized, their application in step-growth polymerization has been scarcely investigated. In the present work, we report a new facile photochemical approach for the synthesis of polypyrene (PPy) by step-growth polymerization. Inspired by our previous studies on photoinduced electron-transfer reactions occurring between electron-rich monomers such as thiophene and carbazole derivatives and iodonium salt, we show that pyrene (Py) readily polymerizes under 350 nm irradiation at room temperature in the presence of iodonium salt by consecutive excitation, electron transfer within the exciplex, proton release, and coupling reactions. A detailed investigation on the structural, morphological, electrochemical, and molecular weight characteristics of the polymers revealed that the ratio of iodonium salt/Py plays a crucial role in the chain length and properties. The approach developed here is broadly adaptable to functional pyrenes and other conjugated monomers.
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    Öğe
    Sequential and Simultaneous Photoinduced Radical and Step- Growth Polymerizations of Carbazole Functional Styrene
    (Amer Chemical Soc, 2022) Celiker, Tugba; Altinisik, Sinem; Vaitusionak, Aliaksei; Kostjuk, Sergei V.; Koyuncu, Sermet; Yagci, Yusuf
    Photoinduced radical and step-growth polymerizations of carbazole functional styrene (vinyl phenyl carbazole, VPC) by sequential and one-pot strategies have been investigated. The obtained polymers were characterized by FTIR, H-1-NMR, GPC, UV-Vis, PL, CV, and BET analyses. The theoretical charge distribution and HOMO-LUMO calculation by DFT were well-matched with those obtained from optical and electrochemical measurements. In the sequential approach, visible light-induced free-radical photopolymerization of VPC by using bisacyl phosphineoxide results in the formation of linear polymers with side-chain carbazole moieties. The resulting polymers exhibit a smooth surface as a consequence of decreasing crystallinity. As evidenced by TEM analysis, the subsequent photoiniated step-growth polymerization of the carbazole groups by using diphenyliodonium hexafluorophosphate (DPI) yields hyperbranched and cross-linked polymers with the microspheres on the surface. In the one-pot approach, concomitant photoinitiated free-radical and step-growth polymerizations by using DPI results in the formation of cross-linked polymers with dispersed distribution. The total nitrogen uptake of VPC-based polymers by using Brunauer-Emmett-Teller (BET) surface area was found to be between about 150 and 190 m(2)/g at 77 K.