Lindenthal Sebastian, Fazzi Daniele, Zorn Nicolas F, El Yumin Abdurrahman Ali, Settele Simon, Weidinger Britta, Blasco Eva, Zaumseil Jana
Institute for Physical Chemistry, Heidelberg University, D-69120 Heidelberg, Germany.
Department of Chemistry "Giacomo Ciamician", University of Bologna, 40126 Bologna, Italy.
ACS Nano. 2023 Sep 26;17(18):18240-18252. doi: 10.1021/acsnano.3c05246. Epub 2023 Sep 11.
Graphene nanoribbons are one-dimensional stripes of graphene with width- and edge-structure-dependent electronic properties. They can be synthesized bottom-up in solution to obtain precise ribbon geometries. Here we investigate the optical properties of solution-synthesized 9-armchair graphene nanoribbons (9-aGNRs) that are stabilized as dispersions in organic solvents and further fractionated by liquid cascade centrifugation (LCC). Absorption and photoluminescence spectroscopy reveal two near-infrared absorption and emission peaks whose ratios depend on the LCC fraction. Low-temperature single-nanoribbon photoluminescence spectra suggest the presence of two different nanoribbon species. Based on density functional theory (DFT) and time-dependent DFT calculations, the lowest energy transition can be assigned to pristine 9-aGNRs, while 9-aGNRs with edge-defects, caused by incomplete graphitization, result in more blue-shifted transitions and higher Raman D/G-mode ratios. Hole doping of 9-aGNR dispersions with the electron acceptor FTCNQ leads to concentration dependent bleaching and quenching of the main absorption and emission bands and the appearance of red-shifted, charge-induced absorption features but no additional emission peaks, thus indicating the formation of polarons instead of the predicted trions (charged excitons) in doped 9-aGNRs.
石墨烯纳米带是石墨烯的一维条带，其电子特性取决于宽度和边缘结构。它们可以在溶液中自下而上合成，以获得精确的带状几何结构。在这里，我们研究了溶液合成的9-扶手椅型石墨烯纳米带（9-aGNRs）的光学性质，这些纳米带在有机溶剂中稳定分散，并通过液体级联离心（LCC）进一步分级。吸收光谱和光致发光光谱揭示了两个近红外吸收和发射峰，其比值取决于LCC分级。低温单纳米带光致发光光谱表明存在两种不同的纳米带种类。基于密度泛函理论（DFT）和含时DFT计算，最低能量跃迁可归因于原始的9-aGNRs，而由于石墨化不完全导致边缘缺陷的9-aGNRs会导致更多的蓝移跃迁和更高的拉曼D/G模式比值。用电子受体FTCNQ对9-aGNR分散体进行空穴掺杂会导致主要吸收和发射带的浓度依赖性漂白和猝灭，并出现红移的、电荷诱导的吸收特征，但没有额外的发射峰，因此表明在掺杂的9-aGNRs中形成了极化子而不是预测的三重态（带电激子）。
