Structural and Electrochemical Properties of 4-Methyl-4'-(n-mercaptoalkyl) Biphenyls Self-Assembled on the Au(100)-(1 × 1) Surface.

Scanning Tunneling Microscopy (STM) and electrochemical studies were conducted on a series of 4-methyl-4'-(n-mercaptoalkyl) biphenyls CH3(C6H4)2(CH2)nSH (BPn, where n = 1-6) self-assembled on the unreconstructed Au(100)-(1 × 1) surface. The study investigated the role of substrate crystallography in the electrochemical and surface properties of BPn adlayers. Notably, unlike BPn on Au(111)-(1 × 1), short alkane chain BPn (1 to 4) does not induce gold surface vacancies when adsorbed on the Au(100)-(1 × 1) indicating distinct surface chemistry. The adlayers exhibit two coexisting phases (α and β), the presence of which evolves with the number of methylene units. The electrochemical properties of the BPn adlayers are characterized by higher thermodynamic stability during reductive desorption with charge values alternating with the number of methylene units. The molecule adsorption modifies an important parameter such as the work function of the underlying Au(100)-(1 × 1) metal substrate. The reciprocal capacitance exhibits a linear dependence on the length of the alkane spacer. Its change per CH2 group agrees well with the values of n-alkanethiols on Au(111).