A two-dimensional covalent organic monolayer was synthesized from simple aromatic triamine and dialdehyde building blocks by dynamic imine chemistry at the air/water interface (Langmuir-Blodgett method). The obtained monolayer was characterized by optical microscopy, scanning electron microscopy, and atomic force microscopy, which unambiguously confirmed the formation of a large (millimeter range), unimolecularly thin aromatic polyimine sheet. The imine-linked chemical structure of the obtained monolayer was characterized by tip-enhanced Raman spectroscopy, and the peak assignment was supported by spectra simulated by density functional theory. Given the modular nature and broad substrate scope of imine formation, the work reported herein opens up many new possibilities for the synthesis of customizable 2D polymers and systematic studies of their structure-property relationships.

Plasmonic metal nanostructures can concentrate incident optical fields in nanometersized volumes, called hot spots. This leads to enhanced optical responses of molecules in such a hot spot, but also to chemical transformations, driven by plasmon-induced hot carriers. Here, we employ tip-enhanced Raman spectroscopy (TERS) to study the mechanism of these reactions in situ, at the level of a single hot spot. Direct spectroscopic measurements reveal the energy distribution of hot electrons, as well as the temperature changes due to plasmonic heating. Therefore, charge-driven reactions can be distinguished from thermal reaction pathways. The products of the hot-carrierdriven reactions are strikingly similar to the ones known from x-ray or e-beam-induced surface chemistry, despite the >100-fold energy difference between visible and x-ray photons. Understanding the analogies between those two scenarios implies new strategies for rational design of plasmonic photocatalytic reactions and for the elimination of photoinduced damage in plasmon-enhanced spectroscopy.

DNA adopts different conformations based on its environment. We reveal conditions that either preserve the DNA’s physiological B-conformation, even upon its placement in UHV, or lead to a partial B-form to A-form reorganization upon DNA’s deposition on a surface. We use high-resolution AFM to image DNA with a well-defined number of base pairs deposited on mica. To enable the DNA’s adhesion, we either add divalent cations to the DNA solution or functionalize the surface with a silane layer. The contour length of DNA on the silane is always in perfect agreement with the B-form conformation, whereas cation-deposited DNA is always, in some cases up to 20% shorter. We varied the equilibration time, the DNA length, and sequence and compared nicked to non-nicked molecules, thus identifying several factors controlling the DNA’s length. We performed TERS measurements confirming spectroscopically that cation-deposited DNA undergoes a partial B-form to A-form conformational transition upon drying and pinpointed positions along the DNA where this transition was more probable, namely the ends of the molecules. Controlling the conformation of DNA is essential for its nanotechnology applications such as nanotemplating. Our findings could also shed a whole new light on DNA polymer physics, the mechanisms of DNA binding to surfaces, or the abundant contradictory data on DNA’s electrical behavior.

The strategy of anchoring molecular catalysts on electrode surfaces combines the high selectivity and activity of molecular systems with the practicality of heterogeneous systems. The stability of molecular catalysts is, however, far less than that of traditional heterogeneous electrocatalysts, and therefore a method to easily replace anchored molecular catalysts that have degraded could make such electrosynthetic systems more attractive. Here, we apply a non-covalent "click" chemistry approach to reversibly bind molecular electrocatalysts to electrode surfaces via host-guest complexation with surface-anchored cyclodextrins. The host-guest interaction is remarkably strong and allows the flow of electrons between the electrode and the guest catalyst. Electrosynthesis in both organic and aqueous media was demonstrated on metal oxide electrodes, with stability on the order of hours. The catalytic surfaces can be recycled by controlled release of the guest from the host cavities and readsorption of fresh guest. This strategy represents a new approach to practical molecular-based catalytic systems. 3Molecular electrocatalysts can exhibit surprisingly high activities and selectivities that are unmatched by most heterogeneous catalysts. 1,2 Therefore, the development of robust immobilization strategies for these molecular species on electrode surfaces is of great interest if these molecular catalytic activities and selectivities are to be transferred to more practical heterogeneous electrosynthetic systems, 3 which have already shown promising results for CO 2 reduction, water reduction and water oxidation in the context of storage of renewable energy. [4][5][6] Over the past decades, many immobilization strategies have been developed, 7 which can be categorized into covalent binding (achieved by adding anchoring groups such as carboxylate to the catalysts), 8 non-covalent binding (pi-stacking on carbon-based electrodes) 9,10 and polymerization-based binding. [11][12][13] Here, we report a new strategy for surface immobilization of molecular electrocatalysts, which relies on a non-covalent "click" chemistry approach to bind molecular species in welldefined sites on electrode surfaces. 14 The binding of electroactive molecular guests into molecular pockets by means of host-guest complex (HGC) formation has previously been studied by several groups, including those of Stoddart and Kaifer, 15 Reinhoudt 16,17 and Huskens. 18 Liu et al. reported the HGC-formation on gold surfaces with the C 60 monoanion as guest, which was found to be electrochemically stable over prolonged durations. 19 Light-induced electron transfer to and from dye molecules bound via the HGC approach was also demonstrated by Freitag and Galoppini. 20,21 The group of Sun demonstrated the use of HGC to improve electron transfer between a molecular catalyst and a dye molecule bound onto TiO 2 . 22 Among the diverse class of host molecules, cyclodextrins, cucurbiturils and calixarenes are the most studied for HGC formation on different surfaces. 23,24 For cy...

Plasmon‐induced hot carriers enable dissociation of strong chemical bonds by visible light. This unusual chemistry has been demonstrated for several diatomic and small organic molecules. Here, the scope of plasmon‐driven photochemistry is extended to biomolecules and the reactivity of proteins and peptides in plasmonic hot spots is described. Tip‐enhanced Raman spectroscopy (TERS) is used to both drive the reactions and to monitor their products. Peptide backbone bonds are found to dissociate in the hot spot, which is reflected in the disappearance of the amide I band in the TER spectra. The observed fragmentation pathway involves nonthermal activation, presumably by dissociative capture of a plasmon‐induced hot electron. This fragmentation pathway is known from electron transfer dissociation (ETD) of peptides in gas‐phase mass spectrometry (MS), which suggests a general similarity between plasmon‐induced photochemistry and nonergodic reactions triggered by electron capture. This analogy may serve as a design principle for plasmon‐induced reactions of biomolecules.

Synthetic covalent monolayer sheets and their subclass, two-dimensional polymers are of particular interest in materials science because of their special dimensionality which renders them very different from any bulk matter. However, structural analysis of such entities is rather challenging, and there is a clear need for additional analytical methods. The present study shows how tip-enhanced Raman spectroscopy (TERS) can be performed on monomer monolayers and the covalent sheets prepared from them by [4 + 4]-cycloaddition to explore rather complex structural and mechanistic issues. TERS is a surface analytical method that combines the high lateral resolution of scanning probe microscopy (SPM) with a greatly enhanced Raman scattering intensity. The high spatial resolution (<60 nm) and the significantly improved sensitivity (contrast factor of >4000) compared to confocal Raman microscopy provides new insights into the formation of this new and exciting material, namely significant consumption of the reactive units (anthracenes) and exclusion of the alternative [4 + 2]-cycloaddition. Moreover, due to the high lateral resolution, it was possible to find a first spectroscopic hint for step growth as the dominant mechanism in the formation of these novel monolayer sheets. In addition, TERS was used to get first insights into the phase behavior of a comonomer mixture.

A two‐dimensional covalent organic monolayer was synthesized from simple aromatic triamine and dialdehyde building blocks by dynamic imine chemistry at the air/water interface (Langmuir–Blodgett method). The obtained monolayer was characterized by optical microscopy, scanning electron microscopy, and atomic force microscopy, which unambiguously confirmed the formation of a large (millimeter range), unimolecularly thin aromatic polyimine sheet. The imine‐linked chemical structure of the obtained monolayer was characterized by tip‐enhanced Raman spectroscopy, and the peak assignment was supported by spectra simulated by density functional theory. Given the modular nature and broad substrate scope of imine formation, the work reported herein opens up many new possibilities for the synthesis of customizable 2D polymers and systematic studies of their structure–property relationships.

Deterioration of the outstanding optical properties of elemental silver due to atmospheric corrosion compromises its use in the field of plasmonics. Therefore, more chemically inert, but more lossy, metals (e.g., gold) are often used as a compromise. Silver tips for near-field optical microscopy are only utilized by specialized laboratories with in-house tip production facilities. This article presents a time-dependent study of the effect of atmospheric corrosion on the electromagnetic enhancement of solid silver tips. It was found that chemical degradation renders them unusable for tip-enhanced Raman spectroscopy (TERS) within the first two days after production. Furthermore, we present a simple electrochemical method for recovering the enhancing effect of corroded silver tips, as well as for storing freshly prepared probes, for example, for easy shipment. The present work greatly simplifies the experimental aspects of near-field optical microscopy, which should make near-field optical techniques, and, in particular, TERS, more accessible to the scientific community.