608534-54-9Relevant articles and documents
From branched polyphenylenes to graphite ribbons
Wu, Jishan,Gherghel, Lileta,Watson, Mark D.,Li, Jixue,Wang, Zhaohui,Simpson, Christopher D.,Kolb, Ute,Muellen, Klaus
, p. 7082 - 7089 (2003)
This article presents the synthesis of graphitic nanoribbons (～1 nm wide), containing extended conjugated all-benzenoid segments. These were obtained by intramolecular oxidative cyclodehydrogenation of soluble branched polyphenylenes 6, which were prepared by repetitive Diels-Alder cycloaddition of 1,4-bis(2,4,5-triphenylcyclopentadienone-3-yl)benzene (1) and diethynylterphenyl (5) in good yield. While insolubility of the obtained graphite ribbons 7 precluded standard spectroscopic structure elucidation, the electronic and vibrational properties were probed by solid-state UV-vis, Raman, and infrared spectroscopy. A wide and unstructured absorption band covering the visible range of the electronic spectrum (λmax ～ 800 nm) is observed, confirming the highly extended conjugated framework. The structure proof of the ribbon-type polymer is supported by the inclusion of appropriate model compounds. The profile of the visible Raman spectrum of the material is similar to that of a discrete polycyclic aromatic hydrocarbon (PAH) C222H42, characterized by two strong bands (at 1603 and 1322 cm-1), corresponding to the G and D bands of graphite. The obtained graphite ribbons are not linear but rather contain kinks due to the structural design of the polyphenylene precursor. High-resolution transmission electron microscopy (HRTEM) images of the graphite ribbons 7 disclose two different domains: one is an ordered graphite layer structure with a layer distance of ca. 3.8 A, and one is disordered due to the existence of kinks in the obtained polymers and/or random stacking of graphite ribbons. Attempts to make linear analogues are so far unsuccessful, emphasizing the critical importance of the geometry of the polyphenylene scaffold to successful oxidative cyclodehydrogenation.
