A spectroscopic study of self-assembled monolayer of porphyrin-functionalized oligo(phenyleneethynylene)s on gold: the influence of the anchor moiety

Abstract

Porphyrin-functionalized oligo(phenyleneethynylene)s (OPE) are promising molecules for molecular electronics applications. Three such molecules (1-3) with the common structure P-OPE-AG (P and AG are a porphyrin and anchor group, respectively) and different anchor groups, viz. an acetyl protected thiol, -S-COCH3 (1), an acetyl protected thiol with methylene linker, -CH2-S-COCH3 (2), and a trimethylsilylethynyl group, -C(triple bond)C-Si(CH3)3 (3) have been synthesized and the corresponding self-assembled monolayers (SAMs) on Au(111) substrates have been prepared. The integrity and structural properties of these films were studied by X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy. The results suggest that the films formed from 1 have a high orientational order with an almost upright orientation and dense packing of the molecular constituents, i.e. represent a high quality SAM. In contrast, molecule 2 formed disordered molecular layers on Au, even though the molecule-surface bonding (thiolate) is the same as in the case of molecule 1. This suggests that the methylene linker in molecule 2 has a strong impact on the quality of the resulting film, so that a well-ordered SAM cannot be formed. The silane system, 3, is also able to bind to the gold surface but the resulting SAM has a poor quality, being significantly disordered and/or comprised of strongly inclined molecules. The above results suggest that the nature of the anchor group along with a possible linker is an important parameter which, to a high extent, predetermines the entire quality of OPE-based molecular layers.

Surface modification of silica-coated gadolinium oxide nanoparticles with zinc tetracarboxyphenoxy phthalocyanine for the photodegradation of Orange G

“…The sources of the other peaks are not yet known. These results, however, confirm that a silica shell has been assembled on the surface of the nanoparticle [42].…”

“…This was to be expected as XPS is a surface sensitive technique (where typically the photoelectrons generated are from within the first 3 nm of the surface being analyzed) [40]. The survey scan obtained for NP 2 shows instead the characteristic peaks associated with Si (e.g., Si 2p at 100 eV) and an increase in intensity of the N 1s peak at 397 eV; the position of this N 1s peak also indicates successful amino group functionalization [42]. (1 and 2).…”

Porphyrins as Active Components for Electrochemical and Photoelectrochemical Devices

“…The resulting low quality monolayer was found to be loosely packed due to a strong inclination and a random orientation of the macrocycles. 105 Better results in terms of SAM organization and stability were obtained with phosphonates as binding groups. Differently from organosulfur compounds, which do not require any preferential solvent for deposition, phosphonic acids require solvents with a hydrocarbon chain (like 1-butanol) which are co-adsorbed to enhance van der Waals interactions.…”

Single-Molecule Electronics: Chemical and Analytical Perspectives

“…It has also been shown to be possible to form junctions with terminal trimethylsilylethynyl (TMSE, -C≡C-SiMe 3 ) and gold electrodes (75)(76)(77). Trimethylsilylethynyl had been previously shown to be a contacting group for forming stable SAMs on Au (110,(78)(79)(80)(81). In the case of molecular electrical junctions, TMSE was promoted as an anchoring group for simplifying the conductance histograms, given a single low conductance peak was seen rather than the multiple or broad conductance features observed for other anchoring groups such as thiols and pyridyl end groups.…”