應用於氧偵測器的低能隙高分子：合成與電子能帶結構調控

Abstract

本論文主要是利用stille coupling合成含不同予體-受體比例及共平面性的低能隙共軛高分子，以調整共軛高分子的電子能階結構與光物理特性。高分子的電子予體為3-hexylthiophene(3HT)，而電子受體為2,3-bis(2-ethylhexyl)thieno-[3,4-b]pyrazine (TP)，每一單元皆具有長碳鏈烷基做側鏈的修飾，以提升共聚高分子的溶解度。所得的隨機共聚高分子(random copolymer)的組成與進料比有相當程度的差距，可能是因為用於共聚反應的單體的反應性不同，交替共聚高分子(Alternating copolymer)的組成及單體排列方式則可。所得的共聚高分子皆可溶於THF中，熱裂解溫度(Td)在282~357oC間，隨著3HT含量的上升而上升。 各共聚高分子在溶液中的紫外光/可見光的最大吸收(λsol .max)位於557~688nm， 光學能隙(Eg,opt)在1.2~1.28eV。由於主鏈上顯著的電子予體-受體效應，交替共聚高分子相較於P3HT有明顯的紅移，而隨機共聚高分子則因電子予體-受體效應較差，使其在長波長的光學吸收明顯較弱。而共聚物的固態吸收則較溶液吸收有不同程度的紅移，共平面性較好的共聚物有較為明顯的紅移。由循環伏安法(CV)測得的各共聚物電子最高填滿分子軌域(Highest occupied molecular orbital, HOMO)在-4.69~-5.39 eV、電子最低未填滿分子軌域(Lowest unoccupied molecular orbitals, LUMO)位於-3.5~3.91eV，隨著TP比例上升，而HOMO會隨之上升與下降。在組成一樣的高分子中，分子具平面構造者HOMO會較高，而縮小其能隙。希望藉由調控這些低能隙的共聚高分子的組成、單體排列方式及共平面性，我們能得到適合應用在氧偵測器上以提升靈敏度的共軛高分子。

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.