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

Synthesis, Electrochemical Behavior, and Self‐Assembly of Metallocene‐Functionalized Thiofluorenes

“…[31] This tendency is also noticeable in the corresponding fluorenyl compounds 6a and 6b as well as in the ferrocenyl compounds.…”

“…For the isostructural ruthenocene compounds, an irreversible oxidation event was found for the ruthenocene/ ruthenocenium redox couple at E p,ox = 0.58 (6a) and 0.53 V (6b; Figure 4). This is also typical of ruthenocenes, for example, Rc-CϵC-C 6 H 4 -C 6 H 4 -SR [R = H, C(O)Me] [31] or [Ru(η 5 -C 5 H 5 ) 2 ], [59] whereas compounds like [Ru(η 5 -C 5 H 4 PPh 2 ) 2 ] [60,61a] and [Ru(η 5 -C 5 Me 5 )(C 13 Me 8 H)] [62] show a reversible oxidation character. The supporting electrolyte and cyclopentadienyl substituents of the ruthenocene compounds may affect the redox behavior.…”

“…[31] The influence of the different sulfur end-groups in the related ferrocene compounds can also be seen for the ruthenocene molecules.…”

“…Comparison of these values with the potentials of 4a and 4b indicate that 4 is easier to oxidize than 6, as can also be seen by comparing Fc-CϵCH [E°= 0.11 V (∆E = 0.08 V)] [58] with Rc-CϵCH (E ox,p = 0.61 V). [31] Comparative Assessment of the Electrochemical Behavior . [37] It can be seen that the -SHterminated molecules 4b and 8b are easier to oxidize than the analogous S-C(O)Me-protected compounds 4a and 8a, which corresponds to the increased electron density in the ferrocenyl unit.…”

“…[36] In view of the above notion, we recently reported the synthesis and characterization of metallocene-terminated biphenyl ethynyl thiols Mc-CϵC-C 6 H 4 -C 6 H 4 -SH [8b: Mc = (η 5 -C 5 H 4 )(η 5 -C 5 H 5 )Fe; 9b: Mc = (η 5 -C 5 H 4 )(η 5 -C 5 H 5 )Ru] and their use as molecular constituents for the preparation of homogeneous, conformal, and mixed SAMs on Au substrates. [28,31,37] In these molecules, the electrochemically active Mc moieties are connected to the thiol head-group through a biphenyl-alkynyl unit, which is considered to be a relatively good molecular conductor, a prerequisite for the fast transfer of electrochemical signals to the substrate. [37] As an alternative to the biphenyl-alkynyl unit, a dialkylfluorenyl moiety can be considered, which differs from bi-phenyl by a C[(CH 2 ) n CH 3 ] 2 connectivity in the biphenyl backbone.…”