The combined use of laboratory rotational spectroscopy and radio astronomical observations remains the most effective approach for identifying molecules in the interstellar medium (ISM). Following the recent detections of several polycyclic aromatic hydrocarbons (PAHs) and their cyano derivatives in the dense Taurus Molecular Cloud (TMC-1), it is reasonable to extend such searches to other PAHs within the same source. In this work, we report a rotational spectroscopy study of commercially available fluoranthene (FA) and its synthesized cyano derivative, 3-cyanofluoranthene (3-CNFA), using chirped-pulse Fourier-transform microwave spectroscopy. The analysis of the rotational spectra, supported by quantum chemical calculations, yielded molecular parameters for the parent species of both FA and 3-CNFA molecules. The experimental data of 3-CNFA were later used for its astronomical search in TMC-1 with the QUIJOTE line survey but proved unsuccessful. Despite the nondetection of 3-CNFA in this source, the upper limit to its abundance was established. The experimental data will support future astronomical searches in the ISM.

We report the discovery of the 3- and 4-cyano isomers of acenaphthylene (C12H8) using the QUIJOTE line survey of the Taurus molecular cloud 1 (TMC-1). The frequency range of the line survey in the Q band (31.2–50.3 GHz) was complemented with data from a new receiver installed at the Yebes 40m radio telescope that covers the K and Ka bands (18–32 GHz). The identification of 3-cyanoacenaphthylene was based on the detection of 135 individual lines that correspond to 194 rotational transitions. For 4-cyanoacenaphthylene, the lines are slightly weaker, but we identified 37 individual lines that correspond to 66 rotational transitions. As a first step for the identification, we compared the derived rotational constants with their expected theoretical values and obtained a match better than 0.2%. Finally, the new isomers were synthesized in our chemical laboratory and observed in our microwave spectroscopic facilities. The derived laboratory constants match those derived from TMC-1 data perfectly, which confirms our identifications. Lines in the K − Ka band from the previously detected isomers 1- and 5-cyanoacenaphthylene are also reported. The derived column density for 3-cyanoacenaphthylene is (7.0 ± 0.7) × 1011 cm−2, and for the 4-cyano isomer, we derive a column density of (5.0 ± 0.6) × 1011 cm−2. The four possible isomers of cyanoacenaphthylene are finally found in TMC-1. Despite their high relative energies, they exhibit similar abundances (within a factor of ∼2).

In this work, we present an efficient synthetic methodology that allows precise and selective control on the C-C bonds during the Scholl reaction. The first ever described hexabenzocoronene (HBC)-containing helical twistacene NG2 has been obtained with very high yield and practically no need for purification, starting from a helical-twisted hexacene NG1. X-ray analysis reveals an end-to-end twist angle, from approximately 145° in NG1 to 132° in NG2. This approach has provided access to nanographenes (NGs) with improved properties compared to their planar analogues, in particular, enhanced solubility and high stability. In addition, they exhibit interesting redox properties, which, together with their high molar absorbance and optimal energy levels, highlight their potential as new organic semiconductor materials for emerging photovoltaic and electronic technologies.

The present work is aimed toward controlling the atomically precise on-surface synthesis of graphene-based nanostructures regardless of the type of substrate used, a grand scientific challenge that cuts across physics, chemistry, materials science and nanoelectronics. A barrier that has to be surmounted to achieve this goal is the need to overcome the limitations resulting from the hitherto irreplaceable catalytic role of the substrate in the on-surface synthesis of graphene derivatives. In this investigation we present the first experimentally achieved protocol, which allows to perform an on-surface reaction independently from the substrate. We demonstrate a completely new reaction pathway, which is based on replacing the catalytic role of the substrate by an externally dosed gaseous catalyst - an approach that to the best of our knowledge has not yet been proposed in the surface assisted synthesis. The new synthetic approach benefits from the completely counterintuitive application of atomic hydrogen to catalyze the cyclodehydrogenation reaction for planarizing the molecular precursors, which yield the graphene-based nanostructures. Basing the protocol on the externally dosed hydrogen as catalyst, ensures independence from the type of applied surface. Using this approach, we have manufactured differently shaped graphene moieties on a range of surfaces starting from metallic (Au), through semiconducting (TiO 2 and Ge:H), to insulating (Si/SiO 2 and NaCl layers) demonstrating the vast versatility and broad scope of our method. The use of such a wide range of materials required also overcoming barriers in obtaining precise identification of the chemical reaction products. This was achieved through the involvement of complementary techniques such as scanning tunneling microscopy and spectroscopy (STM/STS), non-contact atomic force microscopy (nc-AFM) and secondary ion mass spectrometry (SIMS), corroborated by state-of-the-art first-principles theoretical simulations, which provided the atomic-scale insight into the mechanism of the hydrogen-catalyzed cyclization. The consequences of our findings are far-reaching. We have discovered and utilized a completely new reaction pathway yielding graphene nanostructures on a range of surfaces, including those technologically most interesting and demanded. These findings are highly relevant for chemists and material scientists delivering synthetic routes toward new functional materials, especially merging low-dimensional functional devices with atomically precise and monodisperse graphene units. Our experiments and theoretical simulations also pave the way towards the integration of graphene derivatives in optoelectronic devices as well as developing the field of on-surface synthesis by means of external-catalyzed transformations. It will also inspire merging of atomically shaped graphene-based nanostructures with low dimensional inorganic units into new classes of functional devices. Finally, our transfer of catalytic activity will be in the future beneficial for combination of molecular Π-magnetism with desired non-reactive surfaces, the integration of which has so far been impossible to realize. Figure 1

La integración de la química orgánica con la ciencia de superficies ha permitido avanzar en la síntesis de nanografenos mediante la fusión controlada de anillos bencénicos. Además, las mejoras en las microscopías por sonda de barrido han permitido caracterizar estas nanoestructuras con resolución submolecular. Aunque el desarrollo de la síntesis sobre superficie es relativamente reciente, se han identificado algunas transformaciones que permiten acceder a estructuras fascinantes. La mayoría de las metodologías actuales emplean reacciones inducidas térmicamente y promovidas por superficies metálicas. Sin embargo, también se han introducido estrategias que permiten llevar a cabo reacciones sobre superficies aislantes, por ejemplo, mediante la aplicación de pulsos de voltaje desde la punta del microscopio. Este artículo recoge algunos ejemplos destacados en este campo científico emergente en la interfase entre disciplinas.

We present the discovery of the unsubstituted polycyclic aromatic hydrocarbon (PAH) phenalene (C13H10) in TMC-1 as part of the QUIJOTE line survey. In spite of the low dipole moment of this three-ring PAH, we managed to identify a total of 267 rotational transitions with quantum numbers J and K-a up to 34 and 14, respectively, corresponding to 71 independent frequencies. The identification of this new PAH from our survey was based on the agreement between the rotational parameters derived from the analysis of the lines and those obtained by quantum chemical calculations. Our subsequent chemical synthesis of this PAH and investigation of its laboratory microwave spectrum unequivocally support our identification. We report the column density of phenalene in TMC-1 as (2.8 +/- 1.6) x 10(13) cm(-2).

We report the surface-assisted synthesis of a non-planar cyclophenylene derivative containing four meta- and two para- connected phenylene moieties on Au(111), via hierarchical Ullmann coupling of a 1,10-dibrominated angular [3] phenylene and subsequent C-C bond cleavage at the four-membered rings. Scanning tunneling microscopy and spectroscopy (STM/STS) were used for the characterization of its chemical structure and electronic properties. Density functional theory (DFT) calculations support the experimental observations.

The nickel(0)-catalyzed [2 + 2 + 2] cyclotrimerization of 13,14-picyne, a pi-extended aryne intermediate having bay regions at both sides of the aryne triple bond, has recently enabled the synthesis of an overcrowded triple [7]helicene. In contrast, it has now been found that under palladium(0) catalysis, the same pi-extended aryne intermediate trimerizes in a very different manner, notably featuring a formal 1,7-hydrogen shift coupled with a rare 1,7-palladium aryl-to-aryl migration. Remarkably, this new aryne trimerization reaction seems general and reveals possible using a further pi-extended analog of 13,14-picyne. The two chiral multi[5]helicenes thus obtained have, in addition to helical stereogenic elements, a profoundly hindered stereogenic biaryl axis located in the fjord region of a carbo[5]helicene fragment. Both compounds are characterized by single crystal X-ray diffraction analysis, which reveals their remarkably compact and severely distorted structures. A thorough mechanistic study, combining experiments and DFT simulations, shows that the observed 1,7-Pd aryl-to-aryl migration is a two-step 1,4-to-1,4'-Pd isomerization process enabled by the presence of trace amounts of water, a proton shuttle, in the reaction mixture.

Atomically precise synthesis of graphene nanostructures on semiconductors and insulators has been a formidable challenge. In particular, the metallic substrates needed to catalyze cyclodehydrogenative planarization reactions limit subsequent applications that exploit the electronic and/or magnetic structure of graphene derivatives. Here, we introduce a protocol in which an on-surface reaction is initiated and carried out regardless of the substrate type. We demonstrate that, counterintuitively, atomic hydrogen can play the role of a catalyst in the cyclodehydrogenative planarization reaction. The high efficiency of the method is demonstrated by the nanographene synthesis on metallic Au, semiconducting TiO2, Ge:H, as well as on inert and insulating Si/SiO2 and thin NaCl layers. The hydrogen-catalyzed cyclodehydrogenation reaction reported here leads towards the integration of graphene derivatives in optoelectronic devices as well as developing the field of on-surface synthesis by means of catalytic transformations. It also inspires merging of atomically shaped graphene-based nanostructures with low-dimensional inorganic units into functional devices.

At the same time that our capabilities to synthesize open-shell carbon-based materials are rapidly growing with the development of on-surface synthesis under vacuum conditions, interest in π-magnetism is rising due to its excellent prospects for potential applications. As a result, increasing efforts are being focused on the detailed understanding of open-shell carbon nanostructures and all of the parameters that determine their spin densities and magnetic ground states. Here we present a facile route to synthesize different open-shell acene derivatives with closely related structures by the addition of functional groups. A systematic comparison allows us to draw conclusions on the role of the functional groups and their number and distribution, as well as on the role of the radical state delocalization in relation with the presence or absence of charge transfer at interfaces, which consequently affects the molecule's π-magnetism.

On-surface synthesis has revolutionized the design of low-dimensional organic nanomaterials, introducing unprecedented families of compounds while offering precise control over their structural and functional properties. A critical challenge in this field is achieving regioselective control over covalent bond formation, which is essential for tailoring polymerization processes. Here, we demonstrate a novel approach toward regioselective polymerization on Au(111) using a dicyclopentaanthracene precursor, an acene derivative that comprise two terminal indene moieties. Through a combination of scanning tunneling microscopy, non-contact atomic force microscopy, and density functional theory calculations, we reveal a molecular coverage-dependent regioselective homocoupling mechanism. At low coverage, one-dimensional polymers formed via indenyl couplings in anti-configuration dominate, involving both five-membered rings of the precursor. Increasing the coverage to half a monolayer shifts the regioselectivity, yielding a quasi-1D staircase polymer through indenyl couplings that engage only one five-membered ring of each precursor. At higher coverages, a two-dimensional porous network emerges, driven by the activation of the four benzylic positions of the molecular precursor. Our findings highlight the ability to steer regioselectivity and, consequently, polymer dimensionality by controlling molecular coverage, significantly advancing the fields of on-surface synthesis and polymer science.

Multicomponent reactions are powerful strategies for synthesizing complex molecules in an efficient manner. In this work, we investigate a novel multicomponent reaction involving arynes, imines, and nitriles, leading to chiral β-aminonitriles. Notably, two new bonds (C-C and C-N) are formed in one step without the use of metal catalysts, showing the great potential of this transformation. We demonstrate that this synthetic methodology is compatible with different arynes and imines, and propose a reasonable reaction mechanism initiated by the nucleophilic addition of the imine to the aryne.

π-Conjugated polymers play a crucial role in modern organic optoelectronics and spintronics. However, a key aspect remains unexplored: how to make a π-conjugated polymer able to host intrinsic solitons just by chemical design without the need of external doping. Exploiting on-surface synthesis and to address such challenge, we present a novel chemical reaction based on the regio- and stereo-selective coupling of indenyl moieties for fabricating π-conjugated acenoindenylidene polymers on Au(111) surface, which feature a longitudinal polyacetylene backbone. We address an aspect of polymer design that was experimentally overlooked, namely the relation between structural parity and electronic properties. We discover that odd-membered polymers exhibit an in-gap soliton state, which, thanks to their low bandgaps, spatially extends several nanometers along the longitudinal polyacetylene backbone. Our findings pave the way for the design of π-conjugated polymers that feature highly delocalized quasiparticles simply through chemical design by exploiting structural parity, while eliminating the need for doping.

Starphenes are structurally appealing three‐fold symmetric polycyclic aromatic compounds with potential interesting applications in molecular electronics and nanotechnology. This family of star‐shaped polyarenes can be regarded as three acenes that are connected through a single benzene ring. In fact, just like acenes, unsubstituted large starphenes are poorly soluble and highly reactive molecules under ambient conditions making their synthesis difficult to achieve. Herein, we report two different synthetic strategies to obtain a starphene formed by 19 cata‐fused benzene rings distributed within three hexacene branches. This molecule, which is the largest starphene that has been obtained to date, was prepared by combining solution‐phase and on‐surface synthesis. [19]Starphene was characterized by high‐resolution scanning tunneling microscopy (STM) and spectroscopy (STS) showing a remarkable small HOMO‐LUMO transport gap (0.9 eV).

The interplay between laboratory rotational spectroscopy and radio astronomical observations provides the most effective procedure for identifying molecules in the interstellar medium (ISM). Following the recent interstellar detections of several Polycyclic Aromatic Hydrocarbons (PAHs) and cyano derivatives in the dense molecular cloud TMC-1, it is reasonable to consider searching for other cyano-PAHs in this astronomical source. We present a rotational spectroscopy investigation of the two cyano derivatives of the PAH biphenylene, a plausible reaction product of interstellar benzyne. The rotational spectrum provided molecular parameters for the parent species and 14 monosubstituted isotopologues for each isomer. An accurate equilibrium structure was determined for both isomers using Watson's mass-dependence method (r(m)((2))), offering information on its uncommon ring union. Astronomical searches for the cyanobiphenylene isomers have been undertaken in TMC-1, using the QUIJOTE line survey. No lines of any isomer were found in this astronomical source, but the experimental data will serve to enable future searches for these species in the ISM.

Atomically precise synthesis of nanographenes and graphene nanoribbons on semiconductors and insulators has been a formidable challenge. In particular, the metallic substrates needed to catalyze cyclodehydrogenative planarization reactions of precursor molecules limit subsequent applications that exploit the electronic structure of nanographenes. We demonstrate that, counterintuitively, atomic hydrogen can play the role of a catalyst in the cyclodehydrogenative planarization reaction regardless of the substrate type. The high efficiency of the method was demonstrated by the nanographene synthesis on metallic Au, semiconducting TiO2, as well as on inert and insulating Si/SiO2 and thin NaCl layers.

The on-surface synthesis of an isomer of undecacene, bearing two four-membered rings and two para-quinodimethane moieties, starting from a tetramethyl-substituted diepoxy precursor, is presented. The transformation implies a thermal double deoxygenation followed by a stepwise double dehydrogenation reaction on the Au(111) surface, locally induced by inelastic tunneling electrons. This results in the transformation of para-dimethylbenzene moieties into non-aromatic para-quinodimethanes. The structures and electronic properties of the intermediate and final products are investigated at the single molecule level with high spatial resolution, using both scanning tunneling microscopy/spectroscopy and non-contact atomic force microscopy. The experimental results are supported by density functional theory calculations.

A novel aryne derived from a π-extended biphenylene, 2,3-didehydrobenzo[b]biphenylene, has been developed. The participation of this new aryne building block in [4+2] and palladium-catalyzed [2+2+2] cycloaddition reactions has been effectively applied to the synthesis of a variety of polycyclic conjugated hydrocarbons (PCHs) with appealing structures which combine (aromatic) benzene and (antiaromatic) cyclobutadiene (CBD) rings. Among them, a family of unsubstituted (or barely substituted) CBD-oligoacenes has been accessed by iterative Diels-Alder reactions of the new aryne wit furans and/or isobenzofurans, followed by deoxygenative aromatization of the resulting epoxy-derivatives. The experimental and computational study of the newly synthesized PCHs suggests an important degree of electron delocalization along the polycyclic skeleton, more pronounced in the linearly fused derivatives. Interestingly, the computed ACID plots reveal clockwise current density vectors at the peripheral bonds, originating from the sigma contributions of the antiaromatic cyclobutadiene rings.

The recent interstellar detection of individual polycyclic aromatic hydrocarbons (PAHs) in the dense molecular cloud TMC-1 brings interest in related species that could be present in this astronomical environment. These detections, that include pure PAHs and their cyano-derivative counterparts, were performed through the interplay between laboratory rotational spectroscopy experiments and radioastronomical observations. Here, we present the laboratory rotational spectroscopic study of the five cyano-derivatives of the PAH fluorene (C13H10). The samples for these five species were synthetized in the laboratory and then characterized in the gas phase using a chirped-pulse Fourier-transform microwave spectrometer operating between 2 and 12 GHz. The analysis of the rotational spectra allowed us to derive accurate molecular constants for the five isomers used to obtain frequency predictions that enable astronomical searches of these molecules in the interstellar medium.

The formation of two types of nanographenes from custom designed and synthesized molecular precursors has been achieved through thermally induced intramolecular cyclodehydrogenation reactions on the semiconducting TiO2(110)-(1×1) surface, confirmed by the combination of high-resolution scanning tunneling microscopy (STM) and spectroscopy (STS) measurements, and corroborated by theoretical modeling. The application of this protocol on differently shaped molecular precursors demonstrates the ability to induce a highly efficient planarization reaction both within strained pentahelicenes as well as between vicinal phenyl rings. Additionally, by the combination of successive Ullmann-type polymerization and cyclodehydrogenation reactions, the archetypic 7-armchair graphene nanoribbons (7-AGNRs) have also been fabricated on the titanium dioxide surface from the standard 10,10'-dibromo-9,9'-bianthryl (DBBA) molecular precursors. These examples of the effective cyclodehydrogenative planarization processes provide perspectives for the rational design and synthesis of molecular nanostructures on semiconductors.