Breuer Tobias, Klues Michael, Liesfeld Pauline, Viertel Andreas, Conrad Matthias, Hecht Stefan, Witte Gregor
Fachbereich Physik, Universität Marburg, Renthof 7, 35032 Marburg, Germany.
Department of Chemistry, Humboldt-Universität zu Berlin, 12489 Berlin, Germany.
Phys Chem Chem Phys. 2016 Dec 7;18(48):33344-33350. doi: 10.1039/c6cp06126e.
We report on the synthesis and structural characterization of novel, partially fluorinated hexabenzocoronene (HBC) derivatives. The fluorination of polycyclic aromatic hydrocarbons (PAHs) is a well-established method to enhance the stability of organic semiconductors (OSCs) and render them n-type. For HBC it has been observed that fluorination leads to a modification of the molecular packing motif from a herringbone arrangement to a parallel-packed motif. Here, we study whether this transformation of the molecular packing is also found for the partially fluorinated HBCs 2,5-difluoro-hexa-peri-hexabenzocoronene (FHBC) and 2,5,8,11-tetrafluoro-peri-hexabenzocoronene (FHBC). Combining powder diffraction and NEXAFS dichroism measurements, we reveal that indeed all partially fluorinated compounds adopt a parallel molecular packing, hence maximizing their intermolecular contact area. We identify fluorine-hydrogen bonds as the mediating driving force to specifically stabilize this molecular arrangement and direct self-assembly. Furthermore, we show that the relative orientation of the HBCs on the underlying surface can be precisely controlled by varying the substrate materials. Finally, the energetic states of the compounds are analyzed using photoelectron spectroscopy, optical spectroscopy and density functional theory to identify the effects of fluorination on these fundamental electronic characteristics.
我们报道了新型部分氟化六苯并蔻（HBC）衍生物的合成及结构表征。多环芳烃（PAHs）的氟化是一种成熟的方法，可增强有机半导体（OSCs）的稳定性并使其呈n型。对于HBC，已观察到氟化会导致分子堆积模式从人字形排列转变为平行堆积模式。在此，我们研究这种分子堆积的转变是否也存在于部分氟化的HBCs，即2,5 - 二氟 - 六并六苯并蔻（FHBC）和2,5,8,11 - 四氟 - 并六苯并蔻（FHBC）中。结合粉末衍射和近边X射线吸收精细结构（NEXAFS）二色性测量，我们发现所有部分氟化的化合物确实都采用平行分子堆积，从而使其分子间接触面积最大化。我们确定氟氢键是特异性稳定这种分子排列并引导自组装的介导驱动力。此外，我们表明通过改变基底材料可以精确控制HBCs在基底表面的相对取向。最后，使用光电子能谱、光谱学和密度泛函理论分析化合物的能级状态，以确定氟化对这些基本电子特性的影响。
