Tethered Monolayers of Poly((N-pyrrolyl)alkanethiol) on Au

Abstract

The electrochemical oxidation of pyrrole-terminated, self-assembled alkanethiol monolayers on Au surfaces in dry electrolyte media (<0.005% H2O) results in tethered poly(N-alkylpyrroles) of varying monomer repeat lengths. After pristine (monomeric) monolayers of 10-(N-pyrrolyl)decane-1-thiol (1), 7-(N-pyrrolyl)heptane-1-thiol (2), and 6-(N-pyrrolyl)hexane-1-thiol (3) on Au have been oxidized in nonaqueous electrolyte media, electrochemistry characteristic of poly(N-alkylpyrroles) is observed. Reflection−absorption infrared spectra of the oxidized monolayers exhibit aromatic C−H out-of-plane deformation bands between 700 and 800 cm-1 that can be used to determine the effective conjugation length of the poly(N-alkylpyrroles) produced. The number of monomer repeat units in the backbone ranges from 2 to ∼20 and depends on the oxidation potential applied to the monomeric monolayers. In comparison to the monomeric monolayers, the electrochemically polymerized monolayers are demonstrated to be more stable with respect to exchange by a redox-labeled alkanethiol.

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

“…An appreciable number of papers dealing with SA of polymerogenic systems on electrode surfaces has recently been published [21][22][23][24][25][26][27][28][29][30][31] .…”

“…The formation of a large structure (a "knitted monolayer"), tethered to the Au surface through many thiol bonds, has been suggested. In a following paper 22) the same authors have also studied the electrochemical oxidation of SAMs of compounds 4 and 5, in which a longer alkyl chain is present. Also in this case the polymerisation takes place in dry electrolytic media (a 0.005% H 2 O).…”

“…Thus in these cases coupling to polymer occurs, as depicted in Scheme 3. The poly(21) and poly (22) layers are insoluble both in CHCl 3 and in water. Also the adsorbed layers of 23 -25 show a CV irreversible peak but, different from 21 and 22, further CV does not show any sign of polymer formation.…”

“…As a further support, the separation of the two redox potentials DE 0 (ca 0.15 V) is comparable to that of sexithiophenes in solution 43) . The UV-visible spectra of both poly(21) and poly (22) layers display a maximum absorption at k max = 460 nm. A comparison with the bulk polymers, which display their maxima at 500 -600 nm, confirms the oligomeric nature of the layers.…”

Formation of a Molecular Wire Using the Chemically Adsorbed Monomolecular Layer Having Pyrrolyl Groups

“…The synthesis technique will be reported elsewhere. Although there were some reports of self-assembled monolayer of pyrrole-containing alkanethiol, those were not tried this time, because the selfassembled monolayer of alkanethiol is not so durable for electro-oxidation and it cannot be prepared on an insulator such as a glass plate [4,5].…”