Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 637371, Singapore.
ACS Nano. 2012 Oct 23;6(10):8878-86. doi: 10.1021/nn302876w. Epub 2012 Sep 13.
We studied chemical doping of trans- and cis-azobenzene on graphene by Raman spectroscopy. It was found that the molecule induces hole-doping in graphene through charge transfer. Moreover, the doping level in graphene can be reversibly modulated by a photocontrolled molecular conformation change. As trans-azobenzene isomerizes to the cis configuration under UV irradiation, we probe the dynamic molecular structural evolution of azobenzene on graphene by Raman spectroscopy. Raman analysis indicates the precise orientation of cis-azobenzene on the graphene surface, which brings us further comprehension of the effect of conformation change on the electronic properties of graphene. In particular, the substantial decreases of the doping level and chemical enhancement of the molecular signal are attributed to the weakening of hole transfer from molecule to graphene, owing to the lifting of the electron-withdrawing group away from the graphene. Moreover, the calculation results exhibit the favorable configuration of cis-azobenzene, which is in good agreement with Raman spectroscopic analysis. Our results highlight an approach for employing graphene as a promising platform for probing molecular conformation transition at the submolecular level by Raman spectroscopy.
我们通过拉曼光谱研究了反式和顺式偶氮苯在石墨烯上的化学掺杂。结果发现，分子通过电荷转移诱导石墨烯空穴掺杂。此外，通过光控分子构象变化可以可逆地调节石墨烯中的掺杂水平。由于反式偶氮苯在紫外光照射下异构化为顺式构型，我们通过拉曼光谱研究了偶氮苯在石墨烯上的动态分子结构演变。拉曼分析表明顺式偶氮苯在石墨烯表面的精确取向，这使我们进一步了解构象变化对石墨烯电子性质的影响。特别是掺杂水平的显著降低和分子信号的化学增强归因于从分子到石墨烯的空穴转移减弱，这是由于吸电子基团从石墨烯上脱离。此外，计算结果显示了顺式偶氮苯的有利构型，这与拉曼光谱分析结果吻合较好。我们的结果突出了一种通过拉曼光谱在亚分子水平探测分子构象转变的方法，即将石墨烯作为一个很有前途的平台。
