The impact of [1,2,5]chalcogenazolo[3,4,f]-benzo[1,2,3]triazole structure on the optoelectronic properties of conjugated polymers.

Aydan Alkan, Ece
[1,2,5]Chalcogenazolo[3,4-f]benzo[1,2,3]triazole units are strong electron-acceptor moieties that narrow the band gap of resulting conjugated polymers due to the electron deficiency on both sides of their structure. In this study, the effect of acceptor strength on optoelectronic properties were aimed and investigated by incorporating these moieties into donor-acceptor type conjugated polymers. Central chalcogen atom of the chalcogenazole linkage differentiated as sulfur and selenium to compare their effects on the optoelectronic properties of the polymers. Therefore, two novel conjugated near-IR (NIR) absorbing donor–acceptor type copolymers comprising [1,2,5]chalcogenazolo[3,4-f]-benzo[1,2,3]triazole derivatives as the acceptors and benzodithiophene as the donor, spaced with thiophene as the π-bridge, were designed and synthesized via Stille polycondensation reaction. Branched alkyl chains (the extended 2-octyl-1-dodecyl alkyl chain; -C8C12) were substituted to 5H-[1,2,3]triazolo[4',5':4,5]benzo[1,2-c][1,2,5]thiadiazole and 5H-[1,2,3]triazolo[4',5':4,5]benzo[1,2-c][1,2,5]selenadiazole for enhanced solubility of polymers which ease the processability hence device constructions. The strong electron-withdrawing units lead to a substantial change on the absorption properties via promoting the intramolecular charge transfer (ICT) band alongside the π–π* transition with a wide range of absorption extended to the NIR region. The resultant soluble polymers were characterized via cyclic voltammetry to determine HOMO and LUMO energy levels as -5.00 eV and -3.92 for PSBT and -4.86 eV and -4.04 eV for PSeBT, respectively. Electronic band gaps of the copolymers were calculated as 1.08 eV for PSBT and 0.82 eV for PSeBT, respectively. Finally, an electrochromic device (ECD) was constructed and characterized using the polymer PSeBT, due to its lower band gap and better switching colors displayed in all RGB than its sulfur analogue.
Citation Formats
E. Aydan Alkan, “The impact of [1,2,5]chalcogenazolo[3,4,f]-benzo[1,2,3]triazole structure on the optoelectronic properties of conjugated polymers.,” Thesis (M.S.) -- Graduate School of Natural and Applied Sciences. Chemistry., Middle East Technical University, 2020.