Low Band Gap Polymers for Oxygen Sensors: Syntheses and Band Structure Engineering
Date Issued
2012
Date
2012
Author(s)
Chen, Yi-Feng
Abstract
In this thesis, Stille coupling were employed to synthesize low band conjugated copolymers consisting of electron-donating units (3-hexylthiophene,3HT) and electron-accepting units units, 2,3-bis(2-ethylhexyl)thieno-[3,4-b]pyrazine (TP) in different ratios with varied coplanarity in order to adjust the electronic band structure of the copolymers. Each unit was decorates with long alkyl side chains to enchance the solubility. The compositions of the random copolymers were very different from the feed ratios of the comonomers, which could possibly result from the very distinctive reactivities of the comonomers. Alternating copolymers containing 3HT and TP in 1:1 and 1:2 molar ratios were successfully obstained via Stille coupling, and these copolymers showed reasonable solubility in THF . Thermal decomposition temperatures ranged from 282 oC to 357oC and the thermal stability was enchanced with increasing 3HT content.
The wavelengths of the maximum of optical absorption of these copolymers in THF solution were extended to longer wavelengths (557~688nm) comparing to P3HT due to strong intramolecular donor-acceptor interaction, and the optical band gaps were 1.2~1.28 eV. The thin filmsexhibited red shifts in optical absorptions in comparison with the absorptions in solution, and better coplanarity benefited the red shift. HOMO levels (-4.69~-5.39 eV) and LUMO levels (-3.5~3.91eV), obtained from cyclic voltametry, were elevated and lowered respectivity with increasing TP ratio in the copolymer. The copolymers with strong coplanarity would elevated the HOMO. By tuning the composition, the arrangement and the coplanaity of these TP containing low band gap copolymers, they could be potential candicates for oxygen sensors with enhancing sensitivity.
The wavelengths of the maximum of optical absorption of these copolymers in THF solution were extended to longer wavelengths (557~688nm) comparing to P3HT due to strong intramolecular donor-acceptor interaction, and the optical band gaps were 1.2~1.28 eV. The thin filmsexhibited red shifts in optical absorptions in comparison with the absorptions in solution, and better coplanarity benefited the red shift. HOMO levels (-4.69~-5.39 eV) and LUMO levels (-3.5~3.91eV), obtained from cyclic voltametry, were elevated and lowered respectivity with increasing TP ratio in the copolymer. The copolymers with strong coplanarity would elevated the HOMO. By tuning the composition, the arrangement and the coplanaity of these TP containing low band gap copolymers, they could be potential candicates for oxygen sensors with enhancing sensitivity.
Subjects
low band gap polymer
band structure engineering
oxygen sensor
Type
thesis
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