Self-Assembly of α-Functionalized Terthiophenes on Gold

Abstract

α-Functionalized terthiophenes containing disulfide (−S−T3−H)2 and alkanethiol (HS−(CH2)11−T3−H) anchoring groups have been synthesized for direct immobilization onto gold. Monolayer structures of these compounds are prepared by spontaneous assembly from ethanol solutions on evaporated gold substrates and thoroughly characterized by ellipsometry, contact angle goniometry, infrared and X-ray photoelectron spectroscopy, and cyclic voltammetry. The two molecules coordinate to the gold substrate exclusively via the anchoring groups upon formation of gold−thiolate bonds. The kinetics of monolayer formation vary dramatically for the two compounds. The alkanethiol analogue assembles rapidly, within a few minutes, and forms a densely packed and highly organized monolayer, with the alkyl chains in an almost perfect all-trans conformation and the Cα−Cα axis of the α-T3 units tilted about 14° away from the surface normal. The assembly process is much slower for the disulfide, but an organized monolayer with an average α-T3 chain tilt of about 33° will eventually form when the assembly is allowed to equilibrate with a solution containing the disulfide for at least 1 day. Moreover, the two monolayer assemblies also display a remarkably different electrochemical behavior. The heterogeneous electron-transfer rate at the disulfide-covered gold substrate is almost indistinguishable from that at bare gold, suggesting that the assembly contains a large number of easily accessible defects. An alternative mechanism for explaining the large electron-transfer rate involving electronic coupling via the conjugated π-system of the α-T3 units is also proposed. The electrochemical response is significantly reduced for the HS−(CH2)11−T3−H assembly, but another type of defects, the so-called “shallow defects” originating from sparsely populated areas on the electrode surface, can be identified.

Photoelectrochemical Generation of Electronically Conducting Polymer-Based Hybrid Junctions on Modified Si(111) Surfaces

“…30,31 Moreover, the positions of these two peaks are in accordance with earlier reported values for thiophene. 24,32,33 The S 2s signature appears at a binding energy of 228.5 eV (Figure 4d) characteristic also of the aromatic ring. 34,35 Globally, the atomic ratios deduced from these XPS results together with some IR observations (total loss of the initial ester stretch, weak intensity of the ketone band) indicate that the conversion of 1 into 2 is higher than 80% at least.…”

Self-assembly of mono- and multilayers of polyconjugated conducting polymers

“…The most important fact is that the carboxyhexyl heads form a layer on the ITO surface which is packed loosely enough that redox processes at the tails are not prevented. As a matter of fact it has been found that in the previously mentioned 29) undecylthiolterthiophene 10 a very close packing blocks the electroactivity of the tails.…”

“…Compounds 10 and 11, containing an alkanethiol and a disulfide moiety respectively as anchoring groups, have been synthesised for direct immobilisation onto gold 29) . Both molecules were found to coordinate to the gold substrate exclusively via the S1H and S1S groups to yield gold-thiolate bonds.…”

A practical synthesis of functionalized alkyl‐oligothiophenes for molecular self‐assembly

“…The alkylation gave 52-58% of the desired alkyl-substituted thiophene 2 with a terminal bromide group (Scheme 2.a). In recent studies [19,20], similar alkyl-derivatized thiophenes were obtained by a two or even four step procedure that involved the acylation of the thiophene moiety and the subsequent reduction of the obtained ketone with BH 3 or N 2 H 4 (the latter requiring temporary replacement of the bromide with a hydroquinone ether). The alkylated thiophene derivative was then brominated in the free α-position using N-bromosuccinimide (NBS) in a mixture of acetic acid and chloroform [21] at room temperature and gave the regioselectively brominated thiophene derivative 3 (84-92% yield).…”