Formation and Structure of Self-Assembled Monolayers of Octylthioacetates on Au(111) in Catalytic Tetrabutylammonium Cyanide Solution

Abstract

The formation and structure of self-assembled monolayers (SAMs) by the adsorption of acetyl-protected octylthioacetate (OTA) on Au(111) in a catalytic tetrabutylammonium cyanide (TBACN) solution were examined by means of scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV). Molecular-scale STM imaging revealed that OTA molecules on Au(111) in a pure solvent form disordered SAMs, whereas they form well-ordered SAMs showing a c(4 × 2) structure in a catalytic TBACN solution. XPS and CV measurements also revealed that OTA SAMs on Au(111) formed in a TBACN solution have a stronger chemisorbed peak in the S 2p region at 162 eV and a higher blocking effect compared to OTA SAMs formed in a pure solvent. In this study, we clearly demonstrate that TBACN can be used as an effective deprotecting reagent for obtaining well-ordered SAMs of thioacetyl-protected molecules on gold.

Formation and Structure of Highly Ordered Self-Assembled Monolayers by Adsorption of Acetyl-Protected Conjugated Thiols on Au(111) in Tetrabutylammonium Cyanide Solution

“…In contrast to this result, XPS, ellipsometry, and IRRAS measurements suggested that SAMs derived from direct adsorption of alkanethioacetates have loosely packed and poorly ordered structures, whereas SAMs formed by the corresponding alkanethiols have closely packed and well-ordered structures . STM imaging with molecular-scale spatial resolution also clearly showed that direct adsorption of alkanethioacetates on Au(111) surfaces led to formation of mainly disordered SAMs containing a few striped domains (with a flat-lying adsorption geometry) that have been usually observed for low-coverage alkanethiol SAMs. , On the other hand, Badin et al reported that adsorption of dodecanethioacetates usually generated loosely packed, ordered SAMs with a striped phase and a p × 2√3 structure . There have been no molecular-scale STM results describing the effect of a TBACN deprotection reagent on formation and structure of π-conjugated OPE2-S SAMs on Au(111) from adsorption of OPE2-SAc molecules.…”

“…Organic thiols are the most popular molecules for SAM formation on gold, but they can easily be oxidized to disulfides or other oxidized compounds in solution containing a trace amount of oxygen. , This undesirable oxidation of thiols often generates an inhomogeneous interface structure and structural defects in the SAMs. To overcome this problem, organic thioacetates have been used as a primary alternative for SAM formation due to their robust chemical stability in solution or ambient conditions. ,,− However, it has been suggested that direct adsorption of these molecules onto gold surfaces results in formation of less ordered SAMs and shows slower adsorption kinetics compared to the corresponding thiols. − For instance, scanning tunneling microscopy (STM) , and infrared reflection adsorption spectroscopy (IRRAS) − demonstrated that direct adsorption of simple n -alkanethioacetates on gold mainly led to formation of liquid-like disordered phases. To improve the structural order and quality of SAMs prepared by organic thioacetates, in situ deprotection of the acetyl group is necessary.…”

Thioacetate-Functionalized Fullerene: Redox Properties and Self-Assembly on the Au(111) Surface

“…The precipitate was washed with hexane (2 × 5 mL) and dried under vacuum, 13 mg (7%). The mass spectrum showed a [M] − peak at 941.2, see Figure 4S; 22 22 Monolayer formation.-The monolayers of deprotected thioacetate derivative 3 were formed by dipping the gold substrates in 1 mM toluene/methanol (4:1) solution of 3 containing a catalytic amount (0.5 mol equivalent per fullerene derivative) of TBACN at RT for 24 h. Prior to the immersion of the gold substrates into the solution, the deprotection of the thioacetyl group of thioacetate derivative 3 molecules was achieved by the action of TBACN at 50 • C for 3 h. 23,24 Attempts to obtain an organized fullerenethioacetate monolayer at the electrode surface under similar conditions but without previous deprotection procedure failed. Instead, physical adsorbed fullerene adleyer domains were observed, see Figure 7S.…”

Efficient Spin-Selective Electron Transport at Low Voltages of Thia-Bridged Triarylamine Hetero[4]helicenes Chemisorbed Monolayer

“…In addition, pinholes are present as expected when the thioacetyl-protected thiols self-assemble on gold with the spontaneous removal of the protecting group. 37,38 Increasing the magnification of the scanned area and operating with different tunneling conditions (Figure 1d,e), it is possible to appreciate the presence of disordered dots whose lateral dimensions might be consistent with those of lying molecules, according to theoretical calculations described in detail further in the text. A statistical analysis was performed on Figure 1e extracting, as the peak of a log-normal distribution, an average value for the diameter equal to 1.8 nm (Figure S7b) and estimating a density packing of about 0.6 molecule/nm 2 .…”