Theoretical study of ethynylbenzene adsorption on Au(111) and implications for a new class of self-assembled monolayer.

Density functional calculations of the adsorption of ethynylbenzene on the Au(111) surface show that, after cleavage of the C-H bond, the terminal carbon makes a strong covalent bond to the surface. The bond energy is shown to be about 70 kcal.mol(-1) with the fcc hollow site being most stable and the molecule oriented perpendicular to the surface. Adsorption without elimination of hydrogen is also possible via a hydrogen 1,2 shift to form a vinylidene surface-bound species, or opening of the C-C triple bond and adsorption through the two carbon atoms in a flat conformation. The reaction energy for formation of the surface-bound vinylidene is estimated to be 5 kcal.mol(-1) exothermic relative to the isolated ethynylbenzene and gold substrate.