Self-assembled monolayers of perfluoroterphenyl-substituted alkanethiols: specific characteristics and odd–even effects

Abstract

Self-assembled monolayers (SAMs) formed by perfluoroterphenyl-substituted alkanethiols (C(6)F(5)-C(6)F(4)-C(6)F(4)-(CH(2))(n)-SH, FTPn) with variable length of the aliphatic linker (n = 2 and 3) were prepared on (111) Au and Ag and characterized by a combination of several complementary spectroscopic and microscopic techniques. A specific feature of these systems is the helical conformation of the FTP moieties, which, along with the high electronegativity of fluorine, distinguishes them from the analogous non-fluorinated systems and makes them attractive for different applications. The SAMs were found to be well-defined, highly ordered, and densely packed, which suggests a perfect correlation between the orientations and, in particular, twists of the FTP helices in the adjacent molecules. Significantly, the SAM exhibited pronounced odd-even effects, i.e. a dependence of the molecular orientation and packing density on the length of the aliphatic linker in the target molecules, with parity of n being the decisive parameter and the direction of the effects on Au opposite to that on Ag. The presence of the odd-even effects in the FTPn system brings new aspects into the discussion about the origin and mechanism of these phenomena. Specifically, the helical conformation of the FTP moieties in the dense phase excludes a variation of the intramolecular torsion and molecular twist as the mechanism behind the odd-even effects.

Reusable plasmonic substrates fabricated by interference lithography: a platform for systematic sensing studies

“…). All these molecules have been previously shown to form well‐ordered, densely packed and contamination‐free SAMs on thermally evaporated Au thin film substrates – as in the present study …”

“…) for BP0 and TP0 because this moiety is in direct neighborship to the S atom, which has a higher polarizability than a C atom (–CH 2 group of TP1). For FTP1, the appearance of the corresponding ring breathing modes at higher wavenumbers (around 1450 cm –1 and 1665 cm –1 ) indicates a clear signature of the aromatic ring substitution by strong electron withdrawing fluorine atoms …”

Side‐Group‐Induced Polymorphism in Self‐Assembled Monolayers: 3,5‐Bis(trifluoromethyl)benzenethiolate Films on Au(111)

“…). An alternative assignment is a distinctly different bonding configuration of the S atom as compared with thiolate, but the atomic sulfur description appears to be more realistic here. The C 1s spectra of the TFBT SAMs prepared with an IT of 5 min (Figure b) exhibited two peaks at 284.6 ( 1 ) and 291.9 eV ( 2 ), which were assigned to the phenyl moiety and the carbon atoms in the CF 3 groups, respectively .…”

X-ray spectroscopy characterization of self-assembled monolayers of nitrile-substituted oligo(phenylene ethynylene)s with variable chain length

“…The packing density was estimated by a comparison of the S2p thiolate /Au4f intensity ratios of the target films with those for the reference dodecanethiol (DDT) and hexadecanethiol (HDT) systems (a similar approach was successfully used in [44] and [45]). This ratio is a direct measure of the molecular packing density.…”