Selenium as a Key Element for Highly Ordered Aromatic Self‐Assembled Monolayers

Abstract

Chemical synthesis of selenoacetic acid Se-anthracen-2-yl ester. 2-Bromoanthracene (1.13 g, 4.39 mmol) [1] was dissolved in THF (80 ml), cooled down to -78°C and tert.-butyllithium (5.9 ml, 8.9mmol) was added to this dropwise. After stirring during warming up to 0°C and cooling back to -78°C, black selenium powder (0.35 g, 4.4 mmol) was added. Again stirring upon warming up was done, following by addition of acetyl chloride (0.35 g, 4.5 mmol) into the cooled solution. Upon further stirring at room temperature, a colorless precipitate was formed. After adding water (100 ml), the aqueous phase was extracted with dichloromethane and the resulting organic phase washed with water (200 ml). After removal of the solvent in vacuum the crude yellow product (1.69 g) was subjected to column chromatography (silica, dichloromethane (5%-100%) / petrol ether, then silica, ethylacetate (5%-100% / petrol ether) and recrystallized from toluene yielding a yellow solid (0.40 g, 1.3 mmol, 30% 197.02, 135.86, 132.23, 131.89, 131.76, 131.30, 130.80, 129.01, 128.25, 128.15, 126.49, 126.32, 125.87, 125.74, 123.74, 34.17. . For background compensation all data were normalized by subtraction of a spectrum which was

Analysis of the near-edge X-ray-absorption fine-structure of anthracene: A combined theoretical and experimental study

“…This approach exploits the fact that the intensity of π* resonances depend on the relative orientation of E according to I(π * ) ∝ |E · T| 2 , where T denotes the transition dipole moment which is oriented normal to the ring plane of aromatic molecules [1]. In a previous study it has been shown that aromatic self-assembled monolayers (SAMs) with anthracene backbones can be prepared with remarkable long-range ordering when selenolates are used as anchoring groups [34]. Therefore, the corresponding NEXAFS data of an anthraceneselenolate SAM are included for comparison in Fig.…”

“…• (for details of the analysis see [34]). In order to determine the orientation of the anthracene backbone also the herringbone packing motif within the film has to be taken into account.…”

“…To provide high resolution reference data without intensity variations of individual resonances due to orientational effects and to exclude electronic distortions owing to chemical interaction with the supporting substrate the present NEXAFS data were acquired for powder samples and are compared with calculated spectra. The spectra are further compared with previous NEXAFS experiments carried out for longrange ordered and highly oriented anthracene-based selfassembled monolayers (SAMs) [34] which reveal the influence of the anchoring unit on the NEXAFS signature of the aromatic backbone and also enable an experimental identification of π*-resonances based on their dichroism. Interestingly, inner-shell electron energy loss spectroscopy (ISEELS) data have been obtained in a previous inelastic electron scattering experiment for gaseous anthracene which had also been simulated in the framework of detailed quantum chemical calculations [35].…”

Modeling the Electronic Properties of π‐Conjugated Self‐Assembled Monolayers

“…[79] Lastly, we note in passing that replacing the thiol docking group with a selenol (ÀSeH) does not affect the interfacial electronic parameters (assuming the same local docking geometry at the interface to the gold substrate), [79] while it significantly increases long-range order in the SAM. [162][163][164][165] To exemplify how the local atomistic structure at the immediate SAM/Au interface can impact the surface electronic structure, we considered SAMs of cyano-, amino-and unsubstituted biphenylthiolate with the sulfurs on-top of gold ad-atoms, which themselves are situated in fcc hollow sites of an otherwise undisturbed Au(111) surface. [115,[123][124][125][126] This structure is not to be confused with the situation also described in Section 2.3.2 in which sulfur pairs share a gold ad-atom.…”

Phase Transition of Octaneselenolate Self-assembled Monolayers on Au(111) Studied by Scanning Tunneling Microscopy

“…22 It was reported that antracene-2-selenol on Au(111) forms long-range ordered SAMs, whereas antracene-2-thiol forms poorly ordered SAMs, which implies that interactions between the headgroup and gold substrate significantly affect the two-dimensional (2D) order and domain formation of SAMs. 23 Nakano et al demonstrated that decaneselenols on gold surfaces generated stable SAMs, as did alkanethiols. 24 The first molecular-scale STM observations of dodecanselenolate SAMs on Au(111) formed from didodecyl diselenide have a unique packing structure: these SAMs have a closely packed distorted hexagonal packing structure with a moiré pattern and a missing-row structure with a (√3 × 3√3)R30 o unit cell, unlike dodecanethiols.…”