Covalent Attachment of Bent-Core Mesogens to Silicon Surfaces

Abstract

Two vinyl-terminated bent core-shaped liquid crystalline molecules that exhibit thermotropic antiferroelectric SmCPA phases have been covalently attached onto a hydrogen-terminated silicon(111) surface. The surface attachment was achieved via a mild procedure from a mesitylene solution, using visible light at room temperature. AFM measurements indicate that a smooth monolayer has been formed. The thickness of the monolayer was evaluated with ellipsometry and X-ray reflectivity. Although the molecules differ in length by four carbon atoms, the thickness of the resulting monolayers was the same. The measured thicknesses correspond quite well with the smectic layer thickness in the bulk liquid crystalline material, suggesting a similar self-organization within the monolayer. From attenuated total reflectance infrared (ATR-IR), which clearly shows the C-H and C-O vibrations, a tilt angle of the mesogens is deduced that also corresponds well with the tilt angle in the liquid crystalline state. X-ray photoelectron spectroscopy (XPS) measurements confirm the high quality of the monolayers, with only marginal silicon oxide formation. The elemental composition and amounts of different O and C atoms deduced from the high-resolution XPS correspond very well with the calculated compositions.

Chemical functionalisation of silicon and germanium nanowires

“…Hydrosilylation involves the incorporation of terminally unsaturated carbon-carbon bonds onto H-terminated Si surfaces. The reaction can be initiated thermally (150-200 C), [55][56][57][58] photochemically (UV [59][60][61][62][63] or visible light 64,65 ), through the presence of a Lewis acid catalyst 66,67 or a radical initiator. 55,68 An alternative approach to the formation of alkylated Si surfaces is via alkyl Grignard (R-MX 2 ) reagents.…”

Silicon-pyrene/perylene hybrids as molecular rectifiers

“…[30] However, direct attachment of the large electroactive organic moieties using preformed ω-arylalkenes remains by and large unexplored except in some rare cases. [31,32] We intended to use the large electroactive PAHs attached to the alkyl moiety via the ether linkage that is chemically more stable than the ester/amide bonds. For this, the late-stage functionalization may be unsuitable, because the chemistry of attaching the organic molecule at the alkyl group will be cumbersome.…”

Amine-terminated silicon nanoparticles: synthesis, optical properties and their use in bioimaging

“…These passivation methods were similar to those developed for planar 33 or porous 34 silicon, for which the attachment can be initiated thermally, 35,36 or photochemically with UV 37 or visible light. 33a, [38][39][40] Hydrosilylation of Si NPs was also successfully performed by using a variety of platinumbased 5,6b or triphenylcarbenium-based catalysts. 42 The light emission of Si nanocrystals has been attributed to the decay of quantum-confined excitons 43 as well as decay mechanisms mediated by surface atoms.…”