Andreas Terfort

Location-selective engineering of chemically identical areas of a complex substrate by the deposition of several different self-assembled monolayers (SAMs) represents a challenge of interfacial nanotechnology. These areas cannot be distinguished by tailoring the anchoring group of the different SAM-forming molecules, since this group, dictated by surface chemistry, should be the same for all these molecules. However, as shown in the present study, such engineering can be potentially performed electrochemically, by the successive assembly of one of the SAMs on all the areas, its controlled removal from selected areas by applying a system-specific reductive desorption potential, and the deposition of the second SAM onto these areas, while the first SAM is preserved in all other regions. The approach was tested with individual samples and several aromatic SAM-forming molecules with either thiolate or selenolate anchoring to the substrate (Au). It worked well for most combinations of these molecules, which provides a reliable basis for its extension to real-life heterogeneous templates, such as circuit boards hosting different types of organic transistors, requiring type-specific interface engineering.

Charge‐transfer excitons (CTXs) at organic donor/acceptor interfaces are crucial intermediates for charge separation in photovoltaic devices. While blends used in real‐world devices hamper detailed characterization of CTXs, atomistic models of cocrystals offer powerful alternatives for gaining microscopic insights. In this work, we investigate electronic and optical properties of acene‐perfluoroacene cocrystals (anthracene, tetracene, and pentacene), combining experimental synthesis and characterization with first‐principles calculations based on many‐body theory. We prepare ultrathin cocrystals for polarization‐resolved transmission‐absorption spectroscopy, linking exciton polarization with molecular packing. Complementing this analysis, density‐functional and many‐body perturbation theory reveal complex excitonic landscapes that challenge several common assumptions about CTXs in weakly interacting donor‐acceptor systems. For the studied cocrystals, we demonstrate that such CTXs are not limited to the absorption onset, but also occur at higher energy and produce sharp, intense absorption features. Adopting the intrinsic molecular coordinate system, we categorize the various excitons according to their polarization and show that the transition dipole moment of the lowest energy CTX is not necessarily aligned with the donor‐acceptor stacking axis. We further characterize triplet excitons from first principles, which are only indirectly accessible experimentally. This work provides a deep understanding of CTXs in organic cocrystals, developing a refined conceptual framework that is crucial for future design of environmentally sustainable photoactive materials.

Metal–Organic Frameworks (MOFs) have diverse applications due to their tunable porosity, large surface area, and diverse chemical functionalities. Among them, one of the most researched MOFs is MIL-101(Cr), which, in addition, is very stable in water. We have used a commercially available substance with approximately 300 nm large crystals for the preparation of a sensing nano-thin layer for the emerging water contaminant PFOS, due to its high selectivity towards this compound. Here, we have synthesized 20 nm sized crystals of MIL-101(Cr), which are among the smallest reported, and compared them to the same material with 300 nm sized crystals. The material was characterized by TEM and XPS. It was possible to prepare insoluble monolayers at the air–water interface (Langmuir films), which were characterized with film compression isotherms, Brewster angle microscopy, and surface potential measurements. The Langmuir–Blodgett (LB) method was used to deposit monolayers on Si wafers and 434 MHz Surface Acoustic Wave resonator simultaneously. The LB layers were very stable over time. The smaller-sized MIL-101 (Cr) crystals exhibit denser, more homogeneous water coverage and packing upon compression, with no observable 10–100 µm aggregates. LB monolayers from the 20 nm particles have approximately six times lower surface roughness. The LB monolayer is far from being smooth, but this will allow excellent access to the MOF pores by the tested analyte in a chemical sensing application. The lack of research on depositing presynthesized MOFs using probably the best method for nanoarchitectonics—the LB method—is addressed. The 20 nm sized MOF crystals are the smallest deposited by this method so far.

Self‐assembled monolayers (SAMs) have long become an important element of modern nanotechnology. Apart from their primary use in tailoring the chemical and physical properties of surfaces and interfaces, they can be modified by physical tools, with electron irradiation being probably the most useful and versatile one. Here, the development and current state of this field is reviewed, addressing both fundamental aspects of this modification and the related implications and applications. Various types of SAMs, differing in their reaction to electron irradiation, are considered, and the impact of relevant factors affecting these reactions, such as the SAM quality, primary electron energy, and temperature, is analyzed. Based on this knowledge, the current applications of SAM engineering by electrons are introduced and discussed. These applications include tuning the SAM properties, preparation of binary SAMs, conventional and chemical lithography, fabrication of carbon nanomembranes (CNMs), enabling metal deposition onto SAMs, and design and fabrication of biointerfaces. Some of these applications, like chemical lithography and functional CNMs, are unique and can hardly be realized with any other technology. They hold significant potential for the future and will presumably soon make a transition from prototype laboratory experiments to real‐life industrial applications.

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are pollutants of concern due to their long-term persistence in the environment and human health effects. Among them, perfluorooctane sulfonic acid (PFOS) is very ubiquitous and dangerous for health. Currently, the detection levels required by the legislation can be achieved only with expensive laboratory equipment. Hence, there is a need for portable, in-field, and possibly real-time detection. Optical and electrochemical transduction mechanisms are mainly used for the chemical sensors. Here, we report the first gravimetric detection of small-sized molecules like PFOS (MW 500) dissolved in water. A 100 MHz quartz crystal microbalance (QCM) measured at the third harmonic and an even more sensitive 434 MHz two-port surface acoustic wave (SAW) resonator with gold electrodes were used as transducers. The PFOS selective sensing layer was prepared from the metal organic framework (MOF) MIL-101(Cr). Its nano-sized thickness and structure were optimized using the discreet Langmuir–Blodgett (LB) film deposition method. This is the first time that LB multilayers from bulk MOFs have been prepared. The measured frequency downshifts of around 220 kHz per 1 µmol/L of PFOS, a SAW resonator-loaded Q_L-factor above 2000, and reaction times in the minutes’ range are highly promising for an in-field sensor reaching the water safety directives. Additionally, we use the micrometer-sized interdigitated electrodes of the SAW resonator to strongly enhance the electrochemical impedance spectroscopy (EIS) of the PFOS contamination. Thus, for the first time, we combine the ultra-sensitive gravimetry of small molecules in a water environment with electrical measurements on a single device. This combination provides additional sensor selectivity. Control tests against a bare resonator and two similar compounds prove the concept’s viability. All measurements were performed with pocket-sized tablet-powered devices, thus making the system highly portable and field-deployable. While here we focus on one of the emerging water contaminants, this concept with a different selective coating can be used for other new contaminants.

Copper(i)–organic frameworks (CuX–bpy) loaded on Cu₂O enable efficient CO₂ photoreduction to formate, leveraging halogens (X = Cl, Br, I) and rapid electron transfer, achieving 1520 μmol g⁻¹ in 12 hours without sacrificial agents or photosensitizers.