Self-assembled monolayers of ferrocene-substituted biphenyl ethynyl thiols on gold

Homogeneous and mixed [with biphenylthiol (BPT)] self-assembled monolayers (SAMs) of ferrocene-substituted biphenyl ethynyl thiols (Fc) were prepared on Au(111) substrates and characterized by several complementary spectroscopic techniques. The mixed films were fabricated either by subsequent immersion of the substrates into the BPT and Fc solutions or by immersion of the substrate into a mixed solution of BPT and Fc. The first procedure resulted in the preparation of high-quality mixed SAMs, in which the Fc molecules were stochastically distributed in the BPT matrix and well-separated from each other. The portion of these molecules in such films could be precisely varied from ca. 7 to 42% by selection of the immersion time in the BPT solution. The films prepared from the mixed solution exhibited a phase separation between the Fc and BPT constituents. These films contained mostly the Fc molecules (similar to 80-90%), showing, thus, a significant deviation from the relative content of the target molecules in the primary solution (a 1: 1 ratio). This finding shows that the Fc molecules, when competing with BPT, preferably adsorb onto Au(111) substrate, suggesting a significant impact of the ferrocene groups onto the structure-building interactions responsible for molecular self-assembly.