A photolabile protection strategy for terminal alkynes

AbstractWe present a strategy for photolabile protection of terminal alkynes. Several photo-caged alcohols were synthesized via mild copper(II)-catalyzed substitution between tertiary propargylic alcohols and 2-nitrobenzyl alcohol to build up robust, base stable o-nitrobenzyl (NB) photo-cleavable compounds. We compare the new photolabile protecting group with the commonly used alkyne protecting group, 2-methyl-3-butyn-2-ol and the results show that NB ethers are stable under the cleaving conditions for the cleavage of methylbutynol protected alkynes. Additionally, we present the synthesis of photo-cleavable NB derivatives containing thiol groups that can serve as agents for photoinduced surface functionalization reactions

Building Blocks for the Assembly of Nanostructures

The natural world and many man made technologies are driven by self-assembly, involving the autonomous organization of individual components as a result of specific local interactions into functional structures. Self-assembly is a platform from which to construct materials with a high complexity, in high precision, with an inbuilt error- correction system due to its dynamic nature. For example, in nature this principle allows us to encode our genome by the controlled opening and closing two stands of DNA. In addition, linear protein chains fold into elaborate 3D structures for specific functions, cells assemble and divide for example into embryonic tissue and form the basis of reproduction. In fact, all these biological components have a high degree of organization owing to specific interactions at molecular level. The principle of self- assembly is also used in technology for example for drug delivery through liposomes made out of lipid bilayers to carry the drug through membranes to reach specific tissues. It is also the basis of many type of biosensors, such as glucose sensors used by diabetics to monitor their blood sugar level. But also future computer based technology may need ordered arrays of molecules, such as rotaxanes. Rotaxanes for example assemble and switch between two states, which is a promising step towards future molecular-based computers. Indeed, society is in a demand for more powerful computers and therefore its working components ideally need further miniaturization. This thesis is focusing on different aspects of the self-assembly. The molecular level, the design of new molecules for the self-assembly on surfaces. We designed several molecules and dyes, such as terpyridines, rhodamines and photolabile molecules, which assemble on metal surfaces. Another aspect of this thesis is the testing and evaluating for possible application, such as in biosensing on surfaces with photolabile compounds. Furthermore, the complex strengths of osmium cations and terpyridin was determined using terpyridine molecules assembled on an AFM tip and on a metal surface. Moreover, a plasmon-exciton hybrid was observed by assembling rhodamine dyes on metal nanostructures. Spectral dips in the scattering spectrum appear due to strong coupling between the molecule and the metal. A third aspect of this work was the synthesis of nanoparticles and its assembly into discrete aggregates such as dimers using different approaches, such as molecular linkers or electrostatic interaction. Heterodimeric NPs were tested in hydrogen uptake experiments on individual particles

Self-Assembly at Interfaces

Due to the microscopic size of single-molecule components, it is impractical to assemble a large number of single-molecule components via direct top-down manipulation. Instead, self-assembly methods, meaning spontaneous ordering and organization of molecules without direct human intervention, are proposed as the most feasible way of building up multiple single-molecule devices [1]. The self-assembly process is directed by weak interactions. In this chapter, we will introduce the basic concepts of self-assembly and put it into a context of single-molecule electronic devices. We will discuss mechanisms of formation of self-assembled monolayers and how typical single-molecule components interact with surfaces. Finally, we will present some recent developments in electrode materials using single molecules

Progress in self-assembled single-molecule electronic devices

Recent years have seen progress in several areas regarding single molecule electronic devices. A number of interesting structure-property relationships have been observed, including vibronic effects, spin transitions, and molecular electronic interference known as quantum interference. Together, these observations highlight what the rich opportunities in molecular design might bring in terms of advanced device properties. Pertinent challenges are related to development of high yield preparative procedures for fabrication of single molecule devices in a parallel and reproducible way. With this highlight article we review recent progress in the field considering self-assembled formation of metal nanogaps incorporating single molecules for single molecule electronics applications. We discuss methods for the formation of the nanogaps as well as methods attempting to achieve single molecule functionality in each individual device

Progress in self-assembled single-molecule electronic devices

Recent years have seen progress in several areas regarding single molecule electronic devices. A number of interesting structure-property relationships have been observed, including vibronic effects, spin transitions, and molecular electronic interference known as quantum interference. Together, these observations highlight what the rich opportunities in molecular design might bring in terms of advanced device properties. Pertinent challenges are related to development of high yield preparative procedures for fabrication of single molecule devices in a parallel and reproducible way. With this highlight article we review recent progress in the field considering self-assembled formation of metal nanogaps incorporating single molecules for single molecule electronics applications. We discuss methods for the formation of the nanogaps as well as methods attempting to achieve single molecule functionality in each individual device

Ultrafast Spinning of Gold Nanoparticles in Water Using Circularly Polarized Light

Controlling the position and movement of small objects with light is an appealing way to manipulate delicate samples, such as living cells or nanoparticles. It is well-known that optical gradient and radiation pressure forces caused by a focused laser beam enables trapping and manipulation of objects with strength that is dependent on the particles optical properties. Furthermore, by utilizing transfer of photon spin angular momentum, it is also possible to set objects into rotational motion simply by targeting them with a beam of circularly polarized light. Here we show that this effect can set similar to 200 nm radii gold particles trapped in water in 2D by a laser tweezers into rotation at frequencies that reach several kilohertz, much higher than any previously reported light driven rotation of a microscopic object. We derive a theory for the fluctuations in light scattering from a rotating particle, and we argue that the high rotation frequencies observed experimentally is the combined result of favorable optical particle properties and a low local viscosity due to substantial heating of the particles surface layer. The high rotation speed suggests possible applications in nanofluidics, optical sensing, and microtooling of soft matter

Research Update: Progress in synthesis of nanoparticle dimers by self-assembly

This article highlights recent advances in the controlled self-assembly of nanoparticles to produce dimeric nanoparticle structures. The relevance of this emergent field is discussed in terms of recent applications in plasmonics and chemical catalysis. The concept of bond-valence applied to nanoparticles will be discussed, emphasizing some general approaches that have been successfully used to build these structures. Further, the asymmetric functionalization of nanoparticles surfaces as a path to drive selective aggregation, the use of biomolecules to self-assemble nanoparticles into dimers in solution, and the confinement of aggregates in small cavities are discussed

Toward Plasmonic Biosensors Functionalized by a Photoinduced Surface Reaction

We present a method for efficient coupling of amine nucleophilic molecules of choice to a nanostructured gold surface via photoinduced surface chemistry. The method is based on photoactive self-assembled monolayers and can be used to functionalize localized surface plasmon resonance (LSPR) based biosensors with biorecognition motifs while reducing nonspecific binding via introduction of hydrophilic units. The photoactive linker molecule, 5-bromo-7-nitroindoline, couples nucleophilic molecules such as biotin ethylenediamine to a surface when exposed to UV-light. The specific, noncovalent recognition between biotin and streptavidin is used for demonstration of a simple biorecognition assay based on the LSPR sensing principle. By doing so, one can envision that the binding of any streptavidin fusion protein, being attached to specific spots at the gold surface, is monitored by an LSPR peak shift. Since the surface functionalization is based on a photoinduced reaction, this method can be used to functionalize the surface in a local and site-specific way, and biomedical applications such as drug-screening platforms, microarrays, solid support protein synthesis, and even single molecule experiments can be envisioned

Controlling deposition of nanoparticles by tuning surface charge of SiO2 by surface modifications

The self-assembly of nanoparticles on substrates is relevant for a variety of applications such as plasmonics, sensing devices and nanometer-sized electronics. We investigate the deposition of 60 nm spherical Au nanoparticles onto silicon dioxide (SiO2) substrates by changing the chemical treatment of the substrate and by that altering the surface charge. The deposition is characterized by scanning electron microscopy (SEM). Kelvin probe force microscopy (KPFM) was used to characterize the surface workfunction. The underlying physics involved in the deposition of nanoparticles was described by a model based on Derjaguin–Landau–Verwey–Overbeek (DLVO) theory combined with random sequential adsorption (RSA). The spatial statistical method Ripley\u27s K-function was used to verify the DLVO–RSA model (ERSA). The statistical results also showed that the adhered particles exhibit a short-range order at distances below ~300 nm. This method can be used in future research to predict the deposition densities of charged nanoparticles onto charged surfaces