Achieving magnetic ordering in low-dimensional materials remains a key objective in the field of magnetism. Herein, coordination chemistry emerges as a powerful discipline to promote the stabilization of magnetism at the nanoscale. We present a thorough study of exemplary two-dimensional metal-organic nanoarchitectures synthesized on a Au(111) substrate, which are rationalized by using surface-science techniques and theoretical calculations. By tuning the stoichiometry, two distinct phases based on the same molecular linker coordinated with Co atoms are obtained, though featuring a different coordination sphere. Remarkably, our combined experimental and theoretical results suggest that for one phase the Co centers have an out-of-plane antiferromagnetic ground state, whereas for the other the Co atoms display in-plane antiferromagnetism. These results pave new avenues for designing two-dimensional (2D) metal-organic magnets and tailoring their inherent magnetic properties.

The temperature‐controlled transformation of organic molecules at interfaces is an incipient yet powerful strategy for tailoring their structural and physico‐chemical properties. In this study, we investigate the substrate‐ and thermal‐selective reactions of bis(3,4‐thiophene‐fused)tetrabromo‐ p ‐benzoquinodimethane molecule ( 1 ), focusing on its behavior at distinct coinage metal interfaces, namely Au(111) and Ag(111). Combining scanning probe microscopy and theory, we demonstrate that its sequential transformations are highly dependent on the substrate material and the specific reaction temperatures. When a benzodithiophene precursor, endowed with = CBr 2 units, is deposited under ultra‐high vacuum (UHV) conditions on both substrates held at room temperature (RT), or annealed to 100 °C in the case of Au(111), a self‐assembly is formed comprising 1D covalent polymers achieved through debromination and homocoupling, which are aligned in a parallel fashion thanks to supramolecular interactions, giving rise to a 2D supramolecular polymer. However, when the substrate is held at or above 175 °C during deposition, the molecular precursors ( 1 ) undergo substrate‐specific intramolecular reactions. On Au(111), a major transformation into pentalenodithiophene species is observed, concomitant with the formation of benzotrithiophene. On Ag(111), instead, pentalenodithiophene species are precluded. These findings highlight the importance of substrate selection and temperature control in enabling precise molecular transformations at the nanoscale.

The design of novel low-dimensional carbon materials is at the forefront of modern chemistry. Recently, on-surface covalent synthesis has emerged as a powerful strategy to synthesize previously precluded compounds and polymers. Here, we report a scanning probe microscopy study, complemented by theoretical calculations, on the sequential skeletal rearrangement of sumanene-based precursors into a coronene-based organometallic network by stepwise intra- and inter-molecular reactions on Au(111). Interestingly, upon higher annealing, the formed organometallic networks evolve into two-dimensional coronene-based covalently linked patches through intermolecular homocoupling reactions. A new reaction mechanism is proposed based on the role of C-Au-C motifs to promote two stepwise carbon-carbon couplings to form cyclobutadiene bridges. Our results pave avenues for the conversion of molecular precursors on surfaces, affording the design of unexplored two-dimensional organometallic and covalent materials.

The exposure of molecules to attosecond extreme-ultraviolet (XUV) pulses offers a unique opportunity to study the early stages of coupled electron-nuclear dynamics in which the role played by the different degrees of freedom is beyond standard chemical intuition. We investigate, both experimentally and theoretically, the first steps of charge-transfer processes initiated by prompt ionization in prototype donor-pi-acceptor molecules, namely nitroanilines. Time-resolved measurement of this process is performed by combining attosecond XUV-pump/few-femtosecond infrared-probe spectroscopy with advanced many-body quantum chemistry calculations. We show that a concerted nuclear and electronic motion drives electron transfer from the donor group on a sub-10-fs timescale. This is followed by a sub-30-fs relaxation process due to the probing of the continuously spreading nuclear wave packet in the excited electronic states of the molecular cation. These findings shed light on the role played by electron-nuclear coupling in donor-pi-acceptor systems in response to photoionization.

The first step in the synthesis of polyaniline doped with dodecylbenzene sulfonic acid is the synthesis of the anilinium dodecylbenzene sulfonate salt obtained through the reaction between aniline and dodecylbenzene sulfonic acid in aqueous medium. In this work, theoretical models were developed to simulate the formation mechanism of this salt in an aqueous medium. Changes in energy, frontier orbitals, gap energy, charge distribution and thermodynamic parameters were calculated. These theoretical results were correlated with the experimental data from the synthesis of the salt and from infrared spectroscopy. Theoretical models suggested that the solubilization of dodecylbenzene sulfonic acid and aniline in water are energetically and thermodynamically favorable processes. Interactions between the frontier orbitals indicated the formation of water-insoluble anilinium dodecylbenzene sulfonate salt. These molecular modeling results agree with experimental data indicating that the theoretical method used was efficient in simulating the reaction system.

Molecules bearing gem -dibromoolefines functionalities have been employed in wet chemistry as intermediates in the well-known Corey-Fuchs homologation of carbonyls to alkynes. This gem -dibromoolefines can be embedded into tetrabromo- p -quinodimethanes (TBQs), which efficiently undergo dehalogenative homocoupling on coinage metal surfaces, namely Au(111) and Ag(111), forming one-dimensional (1D) acene and periacene π-conjugated polymers able to exhibit non-trivial topological properties.[1,2] However, the synthesis of more complex π-conjugated polymers to determine the scope of this new reaction, as well as the synthesis of two-dimensional (2D) polymers by following this chemical methodology are still important challenges. In this context, new dimeric TBQs have been synthesized by wet chemical protocols for their further use in the synthesis of double-strand oligomers. Interestingly, the new systems exhibit many defects, due to the intrinsic nature of the synthesized precursors.[3] In this work, we firstly take advantage of the introduction of heteroatoms at the edges of the monomers in order to grow 1D new π-conjugated polymers which, eventually, collapse into amazing large 2D networks by non-covalent interactions. Moreover, when suitable designed TBQs with both the presence of heteroatoms and steric hindrance, unprecedented 1D and covalently linked 2D π-conjugated polymers are formed. These results have allowed the study of new topologically non-trivial polymers which will be presented and discussed in this communication. [1] Cirera, B., Sánchez-Grande, A., de la Torre, B., Santos J. et al . Nat. Nanotechnol. 2020 , 15 , 437–443. [2] González-Herrero, H., Mendieta-Moreno, J. I., Edalatmanesh, S., Santos, J. et al . Advanced Materials 2021 , 33 , 2104495. [3] Vicent, D. J., Perez-Escribano, M. et al. Chem. Sci. , 2023 , 14 , 10112-10120.

The design of dynamic structures with high recognition host-guest materials capable to host selectively small volatile molecules is an emergent field of research with both fundamental and applied implications. The challenge of exploring novel materials with advanced functionalities has led to the development of dynamic crystalline structures promoted by soft interactions. Here, a new pure organic dynamic framework based on hexakis[60]fullerene that are held together by weak van der Waals interactions is described. This crystalline structure is capable of absorbing and releasing chloroform, through internal structural reorganization. This research provides new insight into the design of organic molecular crystals for selective adsorption applications. A new purely organic supramolecular framework based on hexakis[60]fullerene is capable of absorbing and releasing chloroform through internal structural reorganization.image

The design of a well-ordered arrangement of atoms on a solid surface has long been sought due to the envisioned applications in many different fields. On-surface synthesis of metal-organic networks is one of the most promising fabrication techniques. Hierarchical growth, which involves coordinative schemes with weaker interactions, favours the formation of extended areas with the desired complex structure. However, the control of such hierarchical growth is in its infancy, particularly for lanthanide-based architectures. Here the hierarchical growth of a Dy-based supramolecular nanoarchitecture on Au(111) is described. Such an assembly is based on a first hierarchical level of metallo-supramolecular motifs, which in a second level of hierarchy self-assemble through directional hydrogen bonds, giving rise to a periodic two-dimensional supramolecular porous network. Notably, the size of the metal-organic based tecton of the first level of hierarchy can be tailored by modifying the metal-ligand stoichiometric ratio.

Antiaromatic polycyclic conjugated hydrocarbons (PCHs) are attractive research targets because of their interesting structural, electronic and magnetic properties. Unlike aromatic compounds, the synthesis of antiaromatic PCHs is challenging because of their high reactivity and lack of stability, which stems from the small energy gap between their highest occupied and lowest unoccupied molecular orbitals. Here we describe a strategy for the introduction of antiaromatic units in PCHs via thermally selective intra- and intermolecular ring-rearrangement reactions of dibromomethylene-functionalized molecular precursors upon sublimation on a hot Au(111) metal surface, not available in solution chemistry. The synthetic value of these reactions is proven by the integration of pentalene segments into acene-based precursors, which undergo intramolecular ring rearrangement, and the formation of π-conjugated ladder polymers, linked through cyclobutadiene connections, due to ring-rearrangement and homocoupling reactions of indenofluorene-based precursors. The reaction products are investigated by scanning tunnelling microscopy and non-contact atomic force microscopy, and mechanistic insights are unveiled by computational studies. The synthesis of polycyclic conjugated hydrocarbons with antiaromatic moieties is realized by the thermal rearrangement of dibromomethylene-functionalized molecular precursors on a hot Au(111) metal surface.

Significant advancements have been made in the development of high-performance cadmium telluride (CdTe)-based thin film solar cells. However, studies examining the transient excited-state charge dynamics, which determine the final steady-state device performance, are relatively scarce, particularly under device operando conditions. In this work, we investigated charge recombination and extraction dynamics of CdTe solar cells, in comparison with MAPbI3 and narrow bandgap perovskite-based solar cells, using bias-light intensity-dependent transient photovoltage (TPV) and transient photocurrent (TPC) techniques. We found that trap-assisted recombination is the dominant mechanism in the CdTe device at open-circuit, even at 1 sun illumination. Parameters such as charge density, carrier lifetime, and recombination order were extracted from the TPV/TPC data and successfully used to reproduce the open-circuit voltage and short-circuit current densities of the devices measured at steady-state. Consequently, we conclude that these techniques are effective for characterizing charge recombination and extraction dynamics of CdTe solar cells under operando conditions.

Despite their great potential as molecular building blocks for organic synthesis, tetrabromo-p-quinodimethanes (TBQs) are a relatively unknown family of compounds. Herein, we showcase a series of five derivatives incorporating two tetrabromo-anthraquinodimethane (TBAQ) units linked by π-conjugated spacers of different nature and length. The resulting dimers TBQ1–5 are fully characterised by means of thorough spectroscopic measurements and theoretical calculations. Interestingly, owing to the steric hindrance imposed by the four bulky bromine atoms, the TBAQ fragments adopt a characteristically warped geometry, somehow resemblant of a butterfly, and the novel dimers show a complex NMR pattern with signal splittings. To ascertain whether dynamic processes regarding fluxional inversion of the butterfly configurations are involved, first-principles calculations assessing the interconversion energy barriers are performed. Three possible stereoisomers are predicted involving two diastereomers, thus accounting for the observed NMR spectra. The rotational freedom of the TBAQ units around the π-conjugated linker influences the structural and electronic properties of TBQ1–5 and modulates the electronic communication between the terminal TBAQ moieties. The role of the linker on the electronic properties is investigated by Raman and UV-vis spectroscopies, theoretical calculations and UV-vis measurements at low temperature. TBQ1–5 are of interest as less-explored structural building precursors for a variety of scientific areas. Finally, the sublimation, self-assembly and reactivity on Au(111) of TBQ3 is assessed.

The design and study of π-conjugated polymers has received great attention along the last decades. The relevant optical and electronic properties stemming from their delocalised π-electrons allow for a number of applications in the emerging field of organic electronics. However, the inherent limited solubility of planar π-conjugated systems hinders their development, forcing chemists to introduce ancillary solubilising side-chains. On the other hand, ultrahigh-vacuum on-surface synthesis has become a powerful discipline that enables designing with atomistic precision a new plethora of molecular compounds, polymers, and nanomaterials that otherwise are unachievable by conventional organic chemistry. Herein we present a novel on-surface chemical transformation that allows obtaining π-conjugated acene polymers from simple aromatic molecules carrying =CBr2 functionalities. The deposition of such precursors on an Au(111) surface gives rise to close-packed assemblies. Thermal annealing promotes the debromination of the species that thereafter homocouple and give rise to long anthracene wires linked by acetylene bridges, featuring a bandgap of 1.5 eV (see figure below). When larger acenes or periacenes are used (i.e. pentacene, bisanthene, peripentacene) the resulting polymers undergo dramatic structural and electronic changes. Non-contact-AFM evince that the benzoid subunits evolve from aromatic (anthracene) to quinoid (pentacene, bisanthene...), while the alkyne linkers turn into cumulenic. The STM images allow witnessing the HOMO-LUMO levels crossing from anthracene to pentacene. This swap destabilises the aromatic structure and enables a biradical-quinoid one, that permit almost vanishing bandgaps below 0.35 eV. These findings can also be rationalised by topological band gap theory: DFT, tight binding and GW calculations predict that polymers these quasi-metallic polymers exhibit a topologically non-trivial electronic structure. Our results herald novel pathways to engineer π-conjugated polymers on solid surfaces, addressing the relevant family of acenes and, thus, contributing to develop the field of on-surface chemistry and to steer the design of modern low bandgap polymers. Figure 1

Atomic scale defects significantly affect the mechanical, electronic, and optical properties of π-conjugated polymers. Here we deliberately introduce isolated atomic-scale defects into a prototypical anthracene-ethynylene π-conjugated polymer and carefully examine its local density of states on the atomic scale to show how individual defects modify the inherent electronic and magnetic properties of this one-dimensional systems. Our scanning tunneling and atomic force microscopy experiments, supplemented with density functional theory calculations, reveal the existence of a sharp electronic resonance at the Fermi energy around certain defects, which is associated with the formation of a local magnetic moment accompanied by substantial mitigation of the mobility of charge carriers. While defects in traditionally synthesized polymers lead to arbitrary conformations, our results clearly reflect the preferential formation of low dimensional defects at specific polymer sites, which may introduce the possibility of engineering macroscopic defects in surface-synthesized conjugated polymers.

On-surface synthesis has recently emerged as a powerful strategy to design conjugated polymers previously precluded in conventional solution chemistry. Here, an N-containing pentacene-based precursor (tetraazapentacene) is ex-professo synthesized endowed with terminal dibromomethylene (:CBr2 ) groups to steer homocoupling via dehalogenation on metallic supports. Combined scanning probe microscopy investigations complemented by theoretical calculations reveal how the substrate selection drives different reaction mechanisms. On Ag(111) the dissociation of bromine atoms at room temperature triggers the homocoupling of tetraazapentacene units together with the binding of silver adatoms to the nitrogen atoms of the monomers giving rise to a N-containing conjugated coordination polymer (P1). Subsequently, P1 undergoes ladderization at 200 °C, affording a pyrrolopyrrole-bridged conjugated polymer (P2). On Au(111) the formation of the intermediate polymer P1 is not observed and, instead, after annealing at 100 °C, the conjugated ladder polymer P2 is obtained, revealing the crucial role of metal adatoms on Ag(111) as compared to Au(111). Finally, on Ag(100) the loss of :CBr2 groups affords the formation of tetraazapentacene monomers, which coexist with polymer P1. Our results contribute to introduce protocols for the synthesis of N-containing conjugated polymers, illustrating the selective role of the metallic support in the underlying reaction mechanisms.

Among the plethora of polycyclic structures that have emerged in recent years, indenofluorenes comprise a unique class of compounds due to their potential in organic electronic systems such as OLEDs, OFETs, and OPVCs. However, the synthesis of fully conjugated indenofluorenes without bulky groups on the apical carbons under standard chemistry conditions is not easily accessible. In this regard, on-surface synthesis has appeared as a newly developing field of research, which exploits the use of well-defined solid surfaces as confinement templates to initiate and develop chemical reactions. Here, we demonstrate the successful fabrication of indeno[1,2-b]fluorene π-conjugated polymers linked via cumulene-like connections on well-defined metallic surfaces under ultra-high vacuum conditions. The structure and electronic properties of the formed polymers have been precisely characterized by scanning tunneling microscopy, noncontact atomic force microscopy and scanning tunneling spectroscopy, complemented by computational investigations.

Weak forces can play an essential role in chemical reactions 1 . Controlling such subtle forces in reorganization processes by applying thermal or chemical stimuli represents a novel synthetic strategy and one of the main targets in supramolecular chemistry 2 . Actually, to separate the different supramolecular contributions to the stability of the 3D assemblies is still a major challenge. Therefore, a clear differentiation of these contributions would help in understanding the intrinsic nature as well as the chemical reactivity of supramolecular ensembles. In the present work, a controlled reorganization of an hexakis[60]fullerene-based molecular compound purely governed by the weakest van der Waals interactions known, i.e. the dihydrogen interaction – usually called sticky fingers – is illustrated 3 . This pre-reorganization of the hexakis[60]fullerene under mild conditions allows a further selective hydrogenation of the crystalline material via hydrazine vapors exposure. This unique two-step transformation process is monitored by single-crystal to single-crystal diffraction (SCSC) which allows the direct observation of the molecular movements in the lattice and the subsequent solid–gas hydrogenation reaction 4 . Y. Inokuma, M. Kawano, M. Fujita, Nat. Chem. 2011, 3, 349 – 358. J. Echeverria, G. Aullon, D. Danovich, S. Shaik, S. Alvarez, Nat. Chem. 2011, 3, 323 – 330. Estefania Fernandez-Bartolome et all, Angew. Chem. 2019, 8, 2332-2337. Estefania Fernandez-Bartolome et all, Chem. Science. 2021, 12, 25, 8682-8688. Figure 1

A decade after the report of the first efficient perovskite-based solar cell, development of novel hole-transporting materials (HTMs) is still one of the main topics in this research field. Two of the main advance vectors of this topic lie in obtaining materials with enhanced hole-extracting capability and in easing their synthetic cost. The use of anthra[1,9-bc:5,10-b'c']dithiophene (ADT) as a flat π-conjugated frame for bearing arylamine electroactive moieties allows obtaining two novel highly efficient HTMs from very cheap precursors. The solar cells fabricated making use of the mixed composition (FAPbI3)0.85(MAPbBr3)0.15 perovskite and the novel ADT-based HTMs show power conversion efficiencies up to 17.6% under 1 sun illumination compared to the 18.1% observed when using the benchmark compound 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD). Detailed density functional theory calculations allow rationalization of the observed opto-electrochemical properties and predict a flat molecular structure with a low reorganization energy that supports the high conductivity measured for the best-performing HTM.

Quantum phase transitions (QPTs) driven by quantum fluctuations are transitions between distinct quantum phases of matter. At present, they are poorly understood and not readily controlled. Here, scanning tunneling microscopy (STM) and noncontact atomic force microscopy (nc-AFM) are used to explore atomic scale control over quantum phase transitions between two different topological quantum states of a well-defined π-conjugated polymer. The phase transition is driven by a pseudo Jahn-Teller effect that is activated above a certain polymer chain length. In addition, theoretical calculations indicate the presence of long-lasting coherent fluctuations between the polymer's two quantum phases near the phase transition, at finite temperature. This work thus presents a new way of exploring atomic-scale control over QPTs and indicates that emerging quantum criticality in the vicinity of a QPT can give rise to new states of organic matter.

The design of organometallic complexes is at the heart of modern organic chemistry and catalysis. Recently, on-surface synthesis has emerged as a disruptive paradigm to design previously precluded compounds and nanomaterials. Despite these advances, the field of organometallic chemistry on surfaces is still at its infancy. Here, we introduce a protocol to activate the inner diacetylene moieties of a molecular precursor by copper surface adatoms affording the formation of unprecedented organocopper metallacycles on Cu(111). The chemical structure of the resulting complexes is characterized by scanning probe microscopy and X-ray photoelectron spectroscopy, being complemented by density functional theory calculations and scanning probe microscopy simulations. Our results pave avenues to the engineering of organometallic compounds and steer the development of polyyne chemistry on surfaces.