Lelaidier Tony, Lünskens Tobias, von Weber Alexander, Leoni Thomas, Ranguis Alain, D'Aléo Anthony, Fages Frédéric, Kartouzian Aras, Becker Conrad, Heiz Ulrich
Technische Universität München, Department of Physical Chemistry, Catalysis Research Center, Lichtenbergstr. 4, 85748 Garching, Germany and Aix-Marseille Université, CNRS, CINaM UMR 7325, 13288 Marseille, France.
Technische Universität München, Department of Physical Chemistry, Catalysis Research Center, Lichtenbergstr. 4, 85748 Garching, Germany.
Phys Chem Chem Phys. 2016 Feb 21;18(7):5299-305. doi: 10.1039/c5cp06011g.
1,4-Di-n-octyloxy-2,5-bis(pyren-1-ylethenyl)benzene (bis-pyrene) has been studied by the means of surface cavity ring-down (s-CRD) spectroscopy on an amorphous BK7 glass substrate and scanning tunnelling microscopy (STM) on Au(111). Absorption spectra show a modification of the optical properties as a function of coverage, i.e. appearance of a shoulder around 505 nm followed by a saturation of the intensity of this signal observed at higher coverages. We attribute this shoulder to the change of the molecular orientation between the first and the second monolayer and thus to an interfacial effect. These results are confirmed by scanning tunnelling microscopy (STM) measurements where the bis-pyrene molecules have been deposited on Au(111) at room temperature (RT) and onto a cold substrate. Independently of the temperature in the range from 210 K to RT, the first monolayer is always highly organized. At low temperature bis-pyrene molecules constituting the second monolayer are randomly distributed, suggesting that self-organisation is kinetically hindered. Deposited at room temperature, the molecular diffusion is enhanced and the formation of an organized second layer takes place after storing the sample for 150 minutes at room temperature. A HOMO-LUMO gap of 2.85 eV has been determined by scanning tunnelling spectroscopy, which is in very good agreement with the observed optical transition at 434 nm (2.86 eV) in s-CRD spectroscopy.
通过在非晶态BK7玻璃衬底上进行表面腔衰荡（s-CRD）光谱以及在Au(111)上进行扫描隧道显微镜（STM）研究了1,4-二正辛氧基-2,5-双（芘-1-基乙烯基）苯（双芘）。吸收光谱表明光学性质随覆盖度而变化，即在505 nm左右出现一个肩峰，随后在更高覆盖度下观察到该信号强度饱和。我们将这个肩峰归因于第一和第二单分子层之间分子取向的变化，进而归因于界面效应。通过扫描隧道显微镜（STM）测量证实了这些结果，其中双芘分子已在室温（RT）下沉积在Au(111)上以及冷衬底上。在210 K至RT范围内，与温度无关，第一单分子层总是高度有序的。在低温下，构成第二单分子层的双芘分子随机分布，这表明自组装在动力学上受到阻碍。在室温下沉积时，分子扩散增强，在室温下将样品储存150分钟后形成有序的第二层。通过扫描隧道光谱确定了2.85 eV的HOMO-LUMO能隙，这与在s-CRD光谱中观察到的434 nm（2.86 eV）处的光学跃迁非常吻合。
