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The preparation of monolayers based on an organic radical and its diamagnetic counterpart has been pursued on hydrogen-terminated silicon surfaces. The functional monolayers have been investigated as solid-state metal/monolayer/semiconductor (MmS) junctions showing a characteristic diode behavior which is tuned by the electronic characteristics of the organic molecule. The eutectic gallium–indium liquid metal is used as a top electrode to perform the transport measurements and the results clearly indicate that the SOMO–SUMO molecular orbitals impact the device performance. The junction incorporating the radical shows an almost two orders of magnitude higher rectification ratio (R(|J1V/J–1V|) = 104.04) in comparison with the nonradical one (R(|J1V/J–1V|) = 102.30). The high stability of the fabricated MmS allows the system to be interrogated under irradiation, evidencing that at the wavelength where the photon energy is close to the band gap of the radical there is a clear enhancement of the photoresponse. This is translated into an increase of the photosensitivity (Sph) value from 68.7 to 269.0 mA/W for the nonradical and radical based systems, respectively.

The functionalization of substrates with radical species has been shown to be a promising strategy to confer novel physical and chemical properties to a surface. Urazole radicals are persistent nitrogen-centered radicals that are insensitive to oxygen, making them desirable targets for the functionalization of surfaces. Here, we succeed in the preparation of self-assembled monolayers (SAMs) of a 1-arylurazole radical on Au surfaces using two different approaches. In the first approach, a SAM of a radical precursor on the gold surface is prepared followed by its chemical oxidation to generate the active urazole radical. In the second route, the radical is generated in solution and subsequently grafted on the Au surface. In both cases, the SAMs exhibit active radical behavior, but the SAM prepared by the first approach demonstrates greater surface coverage of the electroactive urazole radical species.

The functionalization of single-walled carbon nanotubes (SWCNTs) with luminescent sp3defects has greatly improved their performance in applications such as quantum light sources and bioimaging. Here, we report the covalent functionalization of purified semiconducting SWCNTs with stable organic radicals (perchlorotriphenylmethyl, PTM) carrying a net spin. This model system allows us to use the near-infrared photoluminescence arising from the defect-localized exciton as a highly sensitive probe for the short-range interaction between the PTM radical and the SWCNT. Our results point toward an increased triplet exciton population due to radical-enhanced intersystem crossing, which could provide access to the elusive triplet manifold in SWCNTs. Furthermore, this simple synthetic route to spin-labeled defects could enable magnetic resonance studies complementary to in vivofluorescence imaging with functionalized SWCNTs and facilitate the scalable fabrication of spintronic devices with magnetically switchable charge transport.

Control over the energy level alignment in molecular junctions is notoriously difficult, making it challenging to control basic electronic functions such as the direction of rectification. Therefore, alternative approaches to control electronic functions in molecular junctions are needed. This paper describes switching of the direction of rectification by changing the bottom electrode material M = Ag, Au, or Pt in M–S(CH2)11S–BTTF//EGaIn junctions based on self-assembled monolayers incorporating benzotetrathiafulvalene (BTTF) with EGaIn (eutectic alloy of Ga and In) as the top electrode. The stability of the junctions is determined by the choice of the bottom electrode, which, in turn, determines the maximum applied bias window, and the mechanism of rectification is dominated by the energy levels centered on the BTTF units. The energy level alignments of the three junctions are similar because of Fermi level pinning induced by charge transfer at the metal–thiolate interface and by a varying degree of additional charge transfer between BTTF and the metal. Density functional theory calculations show that the amount of electron transfer from M to the lowest unoccupied molecular orbital (LUMO) of BTTF follows the order Ag > Au > Pt. Junctions with Ag electrodes are the least stable and can only withstand an applied bias of ±1.0 V. As a result, no molecular orbitals can fall in the applied bias window, and the junctions do not rectify. The junction stability increases for M = Au, and the highest occupied molecular orbital (HOMO) dominates charge transport at a positive bias resulting in a positive rectification ratio of 83 at ±1.5 V. The junctions are very stable for M = Pt, but now the LUMO dominates charge transport at a negative bias resulting in a negative rectification ratio of 912 at ±2.5 V. Thus, the limitations of Fermi level pinning can be bypassed by a judicious choice of the bottom electrode material, making it possible to access selectively HOMO- or LUMO-based charge transport and, as shown here, associated reversal of rectification.

The development of highly sensitive and selective devices for rapid screening of polycyclic aromatic hydrocarbons (PAHs) in water is nowadays a crucial challenge owing to their alarming abundance in the environment and adverse health effects. Herein, inspired by the unique π–stacking interactions taking place between identical small aromatic molecules, a novel, generic, and straightforward methodology to electrochemically determine and discriminate such pollutants is described. Such a method is focused on covalently anchoring different PAHs on an indium tin oxide electrode surface by means of self-assembled monolayers. The surface-anchored PAHs act as recognition units to selectivity interact with a specific PAH target of the same nature. By tailoring the recognition platform with four different model PAH molecules (naphthalene, anthracene, pyrene, and fluoranthene) and carrying out an electronic tongue approximation, the selective discrimination and quantification of the selected PAHs in aqueous samples at ultralow concentrations were achieved impedimetrically, which were also validated using a certified reference PAH mixture.

In this work, the deposition of a persistent organic radical by thermal evaporation on Au, Pt, and graphene is performed. The impact of the deposition parameters and the nature of the substrate on the molecular organization within the deposited film are investigated. The nonplanarity of the molecule and the role of the molecule–molecule and molecule–substrate interactions are discussed. UV photoelectron spectroscopy experiments demonstrate that the radical character, and hence its magnetic and redox properties, is preserved on the three surfaces. The optimized films are electrically characterized by top-contacting the film/substrate system using a liquid metal that permits achievement of a soft contact avoiding damaging the layer. The hysteretic current versus voltage curves obtained from the electrical characterization point to the potential applicability of the studied system as an organic memory. Moreover, the demonstrated feasibility of using a liquid metal is an appealing approach toward the preparation of flexible devices.

A robust electrolyte-gated organic field-effect transistor (EGOFET) able to respond to pH in the range 1–10 is reported. This is realized by exploiting the pH-dependent supramolecular host–guest complexation of imidazole/β-cyclodextrin (β-CD). The sensing protocol is performed by incubating magnetic nanoparticles functionalized with β-CD with imidazole solutions at different pHs and trapping them in a magnetic carbon electrode. Such an electrode is then implemented as gate contact in the EGOFET. At higher pH, the complexation is more favored, resulting in a negative shift of the device transfer characteristics. Remarkably, the carbon gate electrode can be polished and reused and the devices show high stability and reproducibility.

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