共平面性、多元環及側鏈氰基對 Poly(3-hexylthiophene)電子能帶結構的影響

Abstract

IV Abstract In this thesis, factors affecting the electronic energy levels and optical absorptions of poly(3-hexylthiophene) (P3HT) are systematically studied, including the coplanality, the introduction of fused ring on the P3HT main chain and the strong electron withdrawing cyano (-CN) side group. All the polymers are synthesized via Stille coupling to afford reasonably high molecular weight (> 10,000) and good solubility in common organic solvent at room temperature. Considering the effect of coplanality, P3HT with various head-to-tail (HT) percentages in the main chain ranging from 50% to 98% are synthesized with regularly distribution of the twists (head-to-head, HH, configurations). The optical band gap and the electrochemical band gap are in good agreement, increasing with the decrement of the coplanality. The widen bad gaps are attributed to the elevated lowest unoccupied molecular oribital (LUMO) and the lifts are not proportional to the increment in the HH percentages. A small amount of twists in the main chain would significantly elevate the LUMO by 0.2~0.4 eV, along with the suppression of π-π stacking in the spin-coated thin film. Regarding the effect of fused ring in the main chain, cyclopentadithiophene (CPT) is introduced to the P3HT main chain and the resulting copolymers containing CPT and 3HT exhibited energy levels similar to those of regioregular P3HT(rr-P3HT), suggesting the fused ring in the main chain has no effect on the electronic band structure. However, the strong coplanality of CPT enables the formation of aggregations of CPT based copolymers in solution at room temperature. In comparison with rr-P3HT in solid state, the introduction of CPT would not promote the red absorption; in addition, the π-π stacking is inhibited. The employment of strong electron withdrawing CN side groups simultaneous lower both the highest occupied molecular oribital (HOMO) and LUMO by 0.2eV without significantly altering the optical absorption and the molecular packing in thin films.