| Summary: | 碩士 === 國立臺灣大學 === 高分子科學與工程學研究所 === 102 === We employed all-atom molecular dynamics (AAMD) simulation and the quantum mechanical (QM) methods to explore the correlation between the molecular conformation and the UV absorption behaviors of terthiophene-based conjugated polymers. The four model systems examined here are PBTTTV-v, PBTTTV-h, H-PBTTTV-v and H-PBTTTV-h. We focus on the effects of side-chain architecture on the two-dimensional extended conjugation properties of the UV absorption spectra of polythiophenes. First, we observe the molecular conformation displaying disordered state of polymer chains within dilute solution via AAMD. In the PBTTTV-v, PBTTTV-h, H-PBTTTV-v and H-PBTTTV-h molecules, due to a large steric hindrance from the linkage between main chain and side chain, they have broader torsional angle distribution of main chain (τMain chain_A) and side chain (τSide chain_B). Because of the free motion of single bonds, the single bond linkages between main chain and side chain don’t intend to preserve a coplanar conformation as the H-PBTTTV-v and H-PBTTTV-h molecules. In contrast, as for the PBTTTV-v and PBTTTV-h polymers with vinyl linkage tend to keep a coplanar conformation. Then, we explore the UV absorption spectra of PBTTTV-v and PBTTTV-h molecules via QM. We notice that PBTTTV-v and PBTTTV-h have the two-dimensional extended conjugation properties in the UV absorption spectra, which make the UV absorption spectra more complicated. On the other hand, we observe the molecular orbital and discover the electron cloud may scatter along the main chain to side chain. As a result, we constitute several segments from the molecular orbitals by adjusting each segment’s fraction. The resultant UV absorption spectra of PBTTTV-v and PBTTTV-h show good match to the experimental results. When the single bonds are substituted for the vinyl linkages, the UV absorption spectra of H-PBTTTV-v and H-PBTTTV-h dimer show two peaks in the same range. The two absorption peaks are from either the main chain or the side chain. In the future, we will modify the torsional angle of molecular conformation within AAMD. We will systematically explore the correlation between molecular conformation and optoelectronic properties of PBTTTV-v, PBTTTV-h, H-PBTTTV-v and H-PBTTTV-h.
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