Acenes are a class polycyclic aromatic hydrocarbons (PAH’s) consisting of linearly fused benzene rings. Their interesting electronic properties have exposed them to intensive studies. By way of example, pentacene is among the best studied organic semiconductors and has been successfully integrated into several types of devices. However, longer acenes have been studied much less, characterized by a lower stability that makes their synthesis in conventional wet chemistry extremely challenging. In fact, an increasing open shell character is predicted as the acenes grow longer. On-surface chemistry stands as an efficient alternative to synthesize and characterize such acenes. In this study, starting from a heptacene derivative (dibromo-tetrahydroheptacene), we use Scanning Tunneling Microscopy-Spectroscopy (STM-STS) to synthesize and characterize heptacene on Ag(100) under ultra-high vacuum. After depositing the molecules onto the substrate, dehalogenation occurs automatically readily at room temperature. Thereafter, the sequential dehydrogenation of the molecules can be achieved either thermally or using the STM tip, whereby different reactions intermediates are obtained (Fig. 1). As the number of fused benzene rings increases the HOMO-LUMO gap decreases, ending up with an anionic heptacene on the Ag(100) surface. A zero-bias anomaly and strong vibronic fingerprints are observed for specific intermediates.

Resumen del póster presentado al International workshop On-Surface Synthesis (OSS), celebrado en Sant Feliu de Guíxol (España) del 23 al 28 de septiembre de 2018.

Peer reviewed