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This work presents the synthesis of poly(vinylpyrrolidone)-stabilized gold nanoparticles (Au NPs) and their subsequent functionalization with molecules bearing terminal alkynes. The ligand exchange occurs at the liquid-liquid interface (LLI), resulting in the formation of Au NPs stabilized through the covalent C-Au functionalization. Simultaneously, structured composite films are formed, driven by the self-assembly of the Au NPs supported by the polymer. A comparative analysis involving three distinct alkyne-terminated derivatives reveals that film formation is favored when the ligand includes an aromatic unit such as in a ferrocenyl-stilbene derivative. The LLI films can be easily transferred to solid a support for their characterization. Additionally, it is demonstrated that these films serve as a potential electrocatalytic platform. As a proof of concept, we demonstrate that the electrochemically active ferrocene-based Au NPs films can efficiently remove methylene blue via an electro-Fenton-like reaction, surpassing the efficiency of the non-redox phenylacetylene Au NP films.

En este proyecto se ha trabajado para la investigación del efecto CISS en capas de radicales orgánicos. La dataset proporcionada permite poder graficar todos los espectros y otros gráficos que aparacen tanto en el manuscrito princiapl como en la información suplementaria.

Until now, surface-deposited stilbenes have been much less studied than other photochromic systems. Here, an asymmetrically substituted styrene incorporating a redox-active ferrocene moiety and a terminal alkyne group has been synthesised to investigate its photoisomerization in solution, and upon the formation of chemisorbed self-assembled monolayers through a carbon-gold bond formation. Charge transport measurements across the monolayers reveal that upon chemical linkage to the gold substrate there is an alteration of the isomerization pathway, which favours the trans to cis conversion, which is not observed in solution. The experimental observations are interpreted based on quantum chemistry calculations.

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.

General-purpose quantum computation and quantum simulation require multi-qubit architectures with precisely defined, robust interqubit interactions, coupled with local addressability. This is an unsolved challenge, primarily due to scalability issues. These issues often derive from poor control over interqubit interactions. Molecular systems are promising materials for the realization of large-scale quantum architectures, due to their high degree of positionability and the possibility to precisely tailor interqubit interactions. The simplest quantum architecture is the two-qubit system, with which quantum gate operations can be implemented. To be viable, a two-qubit system must possess long coherence times, the interqubit interaction must be well defined and the two qubits must also be addressable individually within the same quantum manipulation sequence. Here results are presented on the investigation of the spin dynamics of chlorinated triphenylmethyl organic radicals, in particular the perchlorotriphenylmethyl (PTM) radical, a mono-functionalized PTM, and a biradical PTM dimer. Extraordinarily long ensemble coherence times up to 148 µs are found at all temperatures below 100 K. Two-qubit and, importantly, individual qubit addressability in the biradical system are demonstrated. These results underline the potential of molecular materials for the development of quantum architectures.

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 optical and chiroptical properties of an aza-HBC-oct-[5]helicene have been studied and also modulated by means of protonation or oxidation. In both cases, the generated species shows a new absorption band in the NIR region that is not present in the neutral species. This result enables this N-doped nanographene to act both as optical and, remarkably, as chiroptical switch since both the CD and CPL can be modulated by external stimuli such as redox or pH changes.

By combining the switching ability of redox molecules with the unique fluorescence properties of quantum dots (QDs), a robust electrochemical fluorescence switch is developed here. This is realized by grafting CdSe/ZnS QDs on transparent indium tin oxide (ITO) substrates and, subsequently, modifying them with a Ferrocene (Fc) molecular monolayer. The application of oxidation/reduction voltage pulses to tune the Fc redox state leads to the tuning of the surface fluorescence output. Interestingly, the ON/OF ratio can be enhanced by reducing the distance between the redox active unit and the QD due to a more efficient electronic coupling. Remarkably, by defining a mixed-valence state, a ternary switch has also been achieved. It is highlighted that the QD surface immobilization is key to realize this switch to avoid aggregation and fluorescence quenching in suspension. Hence, an efficient and versatile novel route to fabricate robust fluorescent redox switches is demonstrated, opening a wide avenue of possibilities to be explored in the field of sensing and information storage.

Two redox and magnetically active perchlorotriphenylmethyl (• PTM) radical units have been connected as end-capping groups to a bis(phenylene)diyne chain through vinylene linkers. Negative and positive charged species have been generated, and the influence of the bridge on their stabilization is discussed. Partial reduction of the electron-withdrawing • PTM radicals results in a class-II mixed-valence system with the negative charge located on the terminal PTM units, proving the efficiency of the conjugated chain for the electron transport between the two terminal sites. Counterintuitively, the oxidation process does not occur along the electron-rich bridge but on the vinylene units. The • PTM radicals play a key role in the stabilization of the cationic species, promoting the generation of quinoidal ring segments.

The functionalization of single-walled carbon nanotubes (SWCNTs) with luminescent sp3 defects 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 vivo fluorescence imaging with functionalized SWCNTs and facilitate the scalable fabrication of spintronic devices with magnetically switchable charge transport.

An organic free radical is a molecule with one or more unpaired electrons. Although most free radicals are highly reactive, chemists have developed a few families of so-called persistent organic radicals with high kinetic stabilities. Polychlorinated trityl radicals, also known as polychlorotriphenylmethyl (PTM) radicals, are particularly chemically stable due to the high steric hindrance provided by the chlorine atoms in ortho positions which protect their single unpaired electron localised on the central carbon atom. In addition to their inherent magnetic spin due to the unpaired electron, PTMs exhibit other appealing properties such as a rich electrochemistry and characteristic optical properties (absorption and emission). Moreover, it has been shown that these properties can be tuned through the preparation of a large library of PTM-based derivatives. Here, we review recent developments employing PTM radicals, which include their implementation in molecular electronic junctions/switches, as building blocks for the preparation of magnetic networks and opto-electronic devices/materials and their exploitation in bio-applications.

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-base

We have investigated the radical functionalization of gold surfaces with a derivative of the perchlorotriphenylmethyl (PTM) radical using two methods: by chemisorption from the radical solution and by on-surface chemical derivation from a precursor. We have investigated the obtained self-assembled monolayers by photon-energy dependent X-ray photoelectron spectroscopy. Our results show that the molecules were successfully anchored on the surfaces. We have used a robust method that can be applied to a variety of materials to assess the stability of the functionalized interface. The monolayers are characterized by air and X-ray beam stability unprecedented for films of organic radicals. Over very long X-ray beam exposure we observed a dynamic nature of the radical–Au complex. The results clearly indicate that (mono)layers of PTM radical derivatives have the necessary stability to withstand device applications.

A push–pull-functionalized stilbene has been prepared, with an electroactive perchlorotriphenylmethyl (PTM) radical and dimethylamine units as electron-withdrawing and -donating moieties, respectively, showing an electrocatalytic redox-induced Z - E isomerization where the open-shell nature of PTM plays a key role in the isomerization ocurrance.

Resistive switching effect is observed for a gallium-indium/gallium oxide/graphene junction. The use of a gallium-based liquid metal alloy, in this case, the eutectic gallium-indium with its native gallium oxide skin, directly provides the metal top contact and the oxide layer needed to fabricate a memory. Graphene is used as bottom electrode due to its electrical properties and, importantly, because it prevents the formation of alloys, leading to a stable simple junction. With this structure, the ON/OFF ratio at 0.5 V between the high resistance state (HRS) and low resistance state (LRS) reached is ~ 104 in ambient conditions. The deposition of an additional switching layer is not needed compared to other resistive random access memories, which makes this system less complex to fabricate. The migration of the oxygen atoms of the oxide layer would be intuitively considered the main reason for the modulation of the tunneling junction resistance but, we suggest that this is not the case and instead of that, charge-trapping/detrapping at the very interface may dominate the switching function.

The incorporation of terminal alkynes into the chemical structure of persistent organic perchlorotriphenylmethyl (PTM) radicals provides new chemical tools to expand their potential applications. In this work, this is demonstrated by the chemical functionalization of two types of substrates, hydrogenated SiO2-free silicon (Si–H) and gold, and, by exploiting the click chemistry, scarcely used with organic radicals, to synthesise multifunctional systems. On one hand, the one-step functionalization of Si–H allows a light-triggered capacitance switch to be successfully achieved under electrochemical conditions. On the other hand, the click reaction between the alkyne-terminated PTM radical and a ferrocene azide derivative, used here as a model azide system, leads to a multistate electrochemical switch. The successful post-surface modification makes the self-assembled monolayers reported here an appealing platform to synthesise multifunctional systems grafted on surfaces.