No abstract

Selective C(sp3) −H activation is of fundamental importance in processing alkane feedstocks to produce high-value-added chemical products. By virtue of on-surface synthesis strategy, we report selective cascade dehydrogenation of n-alkane molecules under surface constraints which yields monodispersed all-trans conjugated polyenes with unprecedented length controllability. We are also able to demonstrate the generality of this concept for alkyl-substituted molecules with programmable lengths and diverse functionalities, and more importantly its promising potential in molecular wiring.

The manipulation of spatial parameters of light is at the cutting edge of optics. It is an interesting and important task to explore wavefront modulation approaches with a continuously tunable working band and dynamically switchable functions. Here, we program the alignment of a polymerizable cholesteric liquid crystal by a dynamic photo-patterning technique. After UV curing and a wash-out-refill process, the designed chiral superstructure is well reconstructed. By this means, a Dammann grating encoded q-plate is fabricated and its function as an optical vortex processor is demonstrated. The working band is electrically tuned and covers a broad range of 137 nm. The switching of mode conversion is achieved on a second scale for given wavelengths based on the electric-driven band shift. This strategy offers a platform for multi-dimensional dynamic control of light and may bring more possibilities to optical imaging, informatics, and micromanipulations.

On-surface synthesis is a powerful methodology for the fabrication of low-dimensional functional materials. The precursor molecules usually anchor on different metal surfaces via similar configurations. The activation energies are therefore solely determined by the chemical activity of the respective metal surfaces. Here, we studied the influence of the detailed adsorption configuration on the activation energy on different metal surfaces. We systematically studied the desulfonylation homocoupling for a molecular precursor on Au(111) and Ag(111) and found that the activation energy is lower on inert Au(111) than on Ag(111). Combining scanning tunneling microscopy observations, synchrotron radiation photoemission spectroscopy measurements, and density functional theory calculations, we elucidate that the phenomenon arises from different molecule−substrate interactions. The molecular precursors anchor on Au(111) via Au−S interactions, which lead to weakening of the phenyl−S bonds. On the other hand, the molecular precursors anchor on Ag(111) via Ag−O interactions, resulting in the lifting of the S atoms. As a consequence, the activation barrier of the desulfonylation reactions is higher on Ag(111), although silver is generally more chemically active than gold. Our study not only reports a new type of on-surface chemical reaction but also clarifies the influence of detailed adsorption configurations on specific onsurface chemical reactions.