| 摘要: | 利用掃描式電子穿隧顯微鏡和循環伏安法探討併環噻吩衍生物在金(111)電極上的排列結構。 首先，探討 Diphenyl dithieno[2,3-b:3,2-d]thiophene (DP-DTT) 、2-Pentafluorophenyl-6-phenyl dithieno[3,2-b;2',3'-d]thiophene (FPP-DTT) 和 2,6-Bis(pentafluorophenyl)dithieno[3,2-b;2',3'-d]thiophene (DFP-DTT) 於金(111)電極上之吸附行為及結構。對於 DP-DTT ，當電位為0.3 V 時，形成整齊結構（2 × 7√3）。電位區間為0.05 至0.2 V，分子於金電極表面形成規則度佳的整齊吸附層且穩定吸附在電極上。然而，將電位調整較0 V 負，分子緩慢的從電極脫附，再將電位往正電位調整，規則的吸附結構會重新吸附在金電極上，代表電位對分子結構的吸脫附是可逆的。而 FPP-DTT 分子在金電極上的吸附層於室溫下有兩種結構(√21 × 3√19)和(12 × √21)，排列整齊的吸附層中，分子列並非均勻分布，而是成對排列，此一現象來自於 FPP-DTT 分子的結構特徵，特別是苯環和全氟苯官能基，由於兩者電荷密度明顯不同，分子內的偶極距，對分子在電極上的排列具有重要的影響。相較於前面敘述的兩個分子， DFP-DTT 分子嘗試不同的條件， 均無法得到排列整齊的分子結構。接著， 2,6-Diphenylthieno[3,2-b]thieno[2',3':4,5]thieno[2,3-d]thiophene (DP-TTA) 在金電極上的吸附層有兩種結構（2 × √39）和(√21 × √39)，隨著溶液濃度、浸泡時間和浸泡溫度的不同，分子的吸附行為也會有所改變。結果顯示，中心結構由 DTT 改變為 TTA 時，其吸附行為不同。 最後， 探討 2,6-Dibenzoyl dithieno[2,3-b:3’,2’-d]thiophene (DB-DTT) 和 2-Benzoyl-6-perfluorobenzoyl dithieno[3,2-b:2',3'-d]thiophene (FBB-DTT) 於金(111)電極上的吸附行為及整齊結構。排列整齊的 DB-DTT ，分子列之間並非等距離。FBB-DTT 分子在金(111)表面形成規則度很好的整齊結構 - (4 × 4√3)，高解像之STM 圖清楚顯示 FBB-DTT 分子兩側的官能基有明顯的高低差，暗端為全氟苯，亮端為苯環，此一結論和理論計算的結果一致，大致上，氟取代基造成苯環上電荷密度降低，使氟苯較不易有穿隧電流通過，因此它導致較低的STM 高度。 In situ scanning tunneling microscopy (STM) was used to reveal the spatial structures of thienothiophene derivatives deposited onto Au(111) electrode from 50 to 100 μM solutions indichlorobenzene. First, the structures of DP-DTT (C6H5-DTT-C6H5), FPP-DTT(C6F5-DTT-C6H5) and DFP-DTT (C6F5-DTT-C6F5) deposited onto Au(111) electrode were examined. For DP-DTT, a disordered adlayer was seen at E > 0.3 V (vs. reversible hydrogen electrode) and was converted into a highly ordered (2 × 7√3)rect - 2 DP-DTT structure when the potential was shifted to 0.2 V. This ordered structure was stable for hours within this potential range. However, switching the potential further more negative to 0 V resulted in the slow desorption of the molecules. The (2 × 7√3)rect - 2DP-DTT ordered adlattices were restored when the potential was made positive to 0.2 V. On the other hand, FPP-DTT was found to arrange in (√21 × 3√19) and (12 × √21) ordered adlattices. Admolecules in both structures were arranged in pairs resulting from dipole – dipole interactions between the phenyl and pentafluorophenyl substituents at room temperature (25。C). In strong contrast to the first two molecules, no ordered structures were observed for DFP-DTT under all experimental conditions employed in this study. Second, the structures of diphenyl (DP- ) – substituted thieno[3,2-b]thieno[2',3':4,5]thieno[2,3-d]thiophene (TTA) deposited on Au(111) electrode were examined。While DP-TTA arranges in well-ordered (2 × √39) and (?21 × √39) structures. The adsorption of DP-TTA varied with experimental conditions, including sample concentration, dosing time and dosing temperature. Lastly, the structures of dibenzoyl (DB- ) - substituted and pentafluorobenzoyl (FBB- )- substituted dithieno[2,3-b:3,2-d]thiophene (DTT) molecules deposited onto Au(111) electrode were studied. DB-DTT formed protracted molecular rows separated by 19 ~ 27 Å. Such a unique arrangement could be ascribed to unlike intermolecular interactions associated with individual molecules with drastically different molecular symmetry. FBB-DTT formed a (4 × 4√3) structure, whose internal molecules structures were discerned by high-resolution STM.Phenyl groups without fluoro-substitutents are considered more electron-rich than those with fluoro-substituent. This disparity in charge distribution is thought to be responsible for their corrugated STM appearances. The former appeared to be 0.04 nm higher than the latter. |
