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We report on the chemical design of chiral molecular junctions with stress-dependent conductance, whose helicity is maintained during the stretching of a single molecule junction due to the stapling of both ends of the inner helix. In the reported compounds, different conductive pathways are observed, with clearly different conductance values and plateau-length distributions, attributed to different conformations of the helical structures. The large chiro-optical responses and the potential use of these molecules as unimolecular spin filters have been theoretically proved using state-of-the-art Density Functional Theory (DFT) calculations, including a fully ab-initio estimation of the CISS-originating spin polarization which is done, for the first time, for a realistic molecular system, We thank the Spanish MICIN for the “María de Maeztu” Programme for Units of Excellence in R&D (grant No. CEX2018-000805-M). Financial support from MCIN/AEI/ 10.13039/501100011033 is acknowledged by L.A.Z. (grant PID2021-125604NB-I00), E. L. (PID2021-127964NB-C21), D. M. and J. M. C. (PID2020-113059GB-C21), A. M. (PID2021-127964NB-C22) and A. O. G. for her FPU contract (FPU16/02597). We also thank the Universidad Autónoma de Madrid and the Comunidad de Madrid (grants No. SI3/PJI/2021-00191, S2018/NMT-4321 through the Nanomag COST-CM Program and E.L. for Atracción de Talento grant 2019-T1/IND-16384). J. J. P. acknowledges financial support from Spanish MICINN (PID2019- 109539GB-C43) and the Generalitat Valenciana through Programa Prometeo/2021/01. This research was also funded by FEDER/Junta de Andalucía-Consejería de Economía y Conocimiento/P20 00162 and the Visiting Scholar Program in the University of Granada. IMDEA Nanociencia acknowleges support from the ’Severo Ochoa’ Programme for Center of Excelence in R&D (CEX2020-001039-S).

A direct, efficient and versatile strategy for the modulation of optoelectronic and magnetic properties of indeno[1,2-b]fluorene has been developed. 4-Substituted-2,6-dimethylphenyl acetylene groups placed in the apical carbon of the five-membered rings lead to redshifted absorption maxima (lmax ranging from 600–700 nm) and considerable narrowing of the HOMO–LUMO energy gap (down to 1.5 eV). Experimental and theoretical data show an increase in the diradical character (y) and a decrease of the singlet-triplet energy gap. Moreover, we have investigated the single-molecule conductance of the antiaromatic indeno[1,2-b]fluorene for the first time by including thiomethyl (-SMe) anchor groups on the phenylacetylene moiety. Conductance values one order of magnitude higher than those of a reference linear 3-ring para-phenylene ethylene have been found, despite the longer length of the S-to- S molecular junction. First principles transport calculations support this high conductance value., MCIN/AEI, ERDF A way of making Europe PGC2018-101873-A-I00 FEDER/Junta de Andalucia-Consejeria de Economia y Conocimiento A-FQM-221-UGR18, Instituto de Salud Carlos III, Spanish Government, European Commission PID2019-106732GB-I00 PID2019-105458RB-I00 PRE2018-083406, 'Severo Ochoa' Programme for Centers of Excellence in RD SEV-2016-0686, 'Maria de Maeztu' Programme for Units of Excellence in RD CEX2018- 000805-M, Ministerio de Universidades FPU19/03751 MCIN/AEI PTA2017-13681-I, Comunidad de Madrid 2019-T1/IND-16384, European Social Fund (ESF)

Using the break junction (BJ) technique we show that Au(RS)2 units play a significant role in thiol-terminated molecular junctions formed on gold. We have studied a range of thiol-terminated compounds, either with the sulfur atoms in direct conjugation with a phenyl core, or bonded to saturated methylene groups. For all molecules we observe at least two distinct groups of conductance plateaus. By a careful analysis of the length behavior of these plateaus, comparing the behavior across the different cores and with methyl sulfide anchor groups, we demonstrate that the lower conductance groups correspond to the incorporation of Au(RS)2 oligomeric units at the contacts. These structural motifs are found on the surface of gold nanoparticles but they have not before been shown to exist in molecular-break junctions. The results, while exemplifying the complex nature of thiol chemistry on gold, moreover clarify the conductance of 1,4-benzenedithiol on gold. We show that true Au-S-Ph-S-Au junctions have a relatively narrow conductance distribution., Comment: 9 pages, 7 figures

A new family of distorted ribbon-shape nanographenes was designed, synthesized and their optical and electrochemical properties were measured, pointing out an unprecedented correlation between their structural characteristics and their two photon absorption (TPA) responses and electrochemical band gaps. Three nanographene ribbons have been prepared: a seven-membered ring containing nanographene presenting a tropone moiety at the edge, its full-carbon analogue and the purely hexagonal one. We have found that the TPA cross-sections and the electrochemical band gaps of the seven-membered ring containing compounds are higher and lower, respectively, than those of the fully hexagonal polycyclic aromatic hydrocarbon (PAH). Interestingly, the difference between presenting or not the electron withdrawing group, barely changes these parameters compared with those of the nanoribbon without the heptagon., European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (ERC-2015-STG-677023) -Ministerio de Ciencia Innovación y Universidades (PGC2018-101181-B-I00) -Ministerio de Economía y Competitividad (BES-2016-076371 and RyC-2013-12943).

A unique rippled nanographene constituted by 52 fused rings is presented in which six out-of-plane motifs are fully fused into a triangular aromatic surface of ca. 2.5 nm size. Three units of an unprecedented fully lateral π-extended octabenzo[5]helicene together with three units of saddle-shaped heptagonal rings are combined in a single structure leading to a well-soluble warped nanographene. The two pairs of possible enantiomers have been isolated and their linear, non-linear and chiroptical properties evaluated, revealing an outstanding quantum yield and brightness values at low energy together with good chiroptical responses both in the absorption and emission, We acknowledge the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (ERC-2015-STG-677023) and the Ministerio de Economía y Competitividad (MINECO, Spain) (CTQ2015-70283- P, UNGR15-CE-3478, BES-2016-076371 and RyC-2013-12943). E.M. thanks the Fundação para a Ciência e a tecnologia (PTDC/NAN-MAT729317/2017 and PTDC/QUI-QFI/29319/2017). We thank the CSIRC-Alhambra from the University of Granada.

The effect of the in-backbone presence of charge-assisted hydrogen bonds (CAHBs) in the conductance of single-molecule junctions has been studied by the scanning tunneling microscope break junction technique. In particular, two amidinium–carboxylate supramolecular complexes of different lengths have been tested. We observed that the ionic character that gives extra stability to the CAHB is a hindrance toward the electron transport through the complexes. Theoretical calculations using the DFT + Σ method indicate that both the highest occupied molecular orbital and lowest unoccupied molecular orbital of the complexes are fully localized in only one of the moieties of the complex explaining the low single-molecular conductance of the compounds.

This feature article focuses on the bottom-up approaches (solution-phase) based on organic synthesis for the preparation of saddle-shaped distorted polycyclic aromatic hydrocarbons (PAHs). We summarise the recent progress on the synthetic strategies followed to obtain well-defined nanographenes containing heptagonal and octagonal carbocycles, highlighting the novel strategy developed by our group together with our recent contributions in the area of distorted aromatics. The presence of seven- or eight-membered rings induces a saddle-shape curvature in the planar network pushing the structure out of the plane, which influences the physical properties exhibited. Some brief details on the optical and electronic properties of these curved nanostructures are also discussed., The European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (ERC-2015-STG-677023) and the Ministerio de Economía y Competitividad (MINECO, Spain) (CTQ2015-70283-P).

Including defects in a ribbon-shaped nanographene leads to a new combination of optical properties: TPA-based upconversion and CPL., Herein we describe a distorted ribbon-shaped nanographene exhibiting unprecedented combination of optical properties in graphene-related materials, namely upconversion based on two-photon absorption (TPA-UC) together with circularly polarized luminescence (CPL). The compound is a graphene molecule of ca. 2 nm length and 1 nm width with edge defects that promote the distortion of the otherwise planar lattice. The edge defects are an aromatic saddle-shaped ketone unit and a [5]carbohelicene moiety. This system is shown to combine two-photon absorption and circularly polarized luminescence and a remarkably long emission lifetime of 21.5 ns. The [5]helicene is responsible for the chiroptical activity while the push–pull geometry and the extended network of sp2 carbons are factors favoring the nonlinear absorption. Electronic structure theoretical calculations support the interpretation of the results.

The design of two dimensional graphene-type materials with an anisotropic electron flow direction in the X- and Y-axes opens the door for the development of novel electronic materials with multiple functions in nanoelectronics. In the present work, we have studied the electronic transport properties of a new family of 2D graphene-graphyne hybrids presenting conformationally free phenylethylene subunits. This system ensures two different conductive pathways that are perpendicular to each other: an acene nanoribbon subunit, in the X-axis, with graphene-type conduction, and a free to rotate phenylethylene subunit, in the Y-axis, in which the magnitude of the conduction depends dynamically on the corresponding torsion angle. Our calculations have confirmed that this system presents two different conduction pathways, which are related to the presence of asymmetric Dirac-type cones. Moreover, the Dirac cones can be dynamically modified in the presence of an external gate electrode, which is unprecedented in the literature, We thank the MICINN (project CTQ-2011.22455) and the Regional Government of Andalucía (project P09-FQM-04571) for financial support and the ‘Centro de Supercomputación de la Universidad de Granada (UGRGRID-CSIRC)’ for computation time. NF and DM thank MICINN for their research contracts

Straightforward path to curved graphene molecules: distorted polycyclic aromatic hydrocarbons including heptagon moieties are obtained from simple precursors., Highly distorted polycyclic aromatic hydrocarbons (PAHs) are predicted to be attractive goals in nanoscience owing to the new properties they can exhibit. We have shown that a variety of functionalized distorted heptagon-containing nanographenes can be easily prepared from simple building blocks by a sequence of Co-catalyzed cyclotrimerization and cyclodehydrogenation reactions. The versatility of this strategy allows easy subsequent enlargement of these nanostructures by Ni-catalyzed cross-coupling and final cyclodehydrogenation reactions. Soluble extended distorted nanographenes 1 and 2 containing heptagon and an edge-shared pentagon–heptagon combination have been synthesized. High distortion of the polycyclic backbone of 2 caused by non-hexagonal rings and a helicene moiety was confirmed by X-ray crystallography. Experimental data reveal promising optical and electronic properties for distorted PAHs with long fluorescence lifetimes (up to 14.5 ns) and low band gaps (down to 2.27 eV). This straightforward and versatile synthetic strategy, the observed long fluorescence lifetimes and the small optical and electrochemical band gaps for the presented compounds may promote the future implementation of distorted graphene molecules in electronic devices.

A new, direct inter- and intramolecular coupling of α,β-unsaturated carbonyl compounds with aryl and alkenyl halides and triflates is developed.

In this work, we show that the unique combination of a nickel catalyst and Cp2TiCl allows the direct conjugate addition of aryl and alkenyl iodides, bromides, and to a lesser extent, chlorides and triflates to α,β-unsaturated carbonyls at room temperature, without requiring the previous formation of an organometallic nucleophile. The reaction proceeds inter- and intramolecularly with good functional group compatibility, which is key for the development of free protecting group methodologies. Carbo- and heterocycles of five- and six-membered rings are obtained in good yields. Moreover, some insights about the mechanism involved have been obtained from cyclic voltammetry, UV–vis, and HRTEM measurements.

The single–molecule conductance of a series of BN-acene-like derivatives has been measured by using scanning tunneling break-junction techniques. A strategic design of the target molecules has allowed us to include azaborine units in positions that unambiguously ensure electron transport through both heteroatoms, which is relevant for the development of customized BN-doped nanographenes. We show that the conductance of the anthracene azaborine derivative is comparable to that of the pristine all-carbon anthracene compound. Notably, this heteroatom substitution has also allowed us to perform similar measurements on the corresponding pentacene-like compound, which is found to have a similar conductance, thus evidencing that B–N doping could also be used to stabilize and characterize larger acenes for molecular electronics applications. Our conclusions are supported by state-of-the-art transport calculations., This work has been supported by the MICINN projects PID2019-105458RB-I00, PID2019-106732GB-I00, PGC2018-101873-A-I00, CTQ2017-85454-C2-1-P, FIS2016-77889-R and MAT2017-88693-R, the European Research Council (ERC) (677023), the FEDER/Junta de Andalucía project A-FQM-221-UGR18 and the Comunidad de Madrid project NanoMagCOST (CM S2018/NMT-4321). We also thank Severo Ochoa Programme for Center of Excellence in R&D (SEV-2016-0686) and María de Maeztu Programme for Units of Excellence in R&D (CEX2018-000805-M). We acknowledge the allocation of computer time by the Red Española de Supercomputación and the Centro de Computación Científica at the Universidad Autónoma de Madrid (CCC-UAM). J.G.F. thanks the PFI program of the MICINN co-financed by the European Social Fund. I.R.M. thanks MICINN for a Personal Técnico de Apoyo contract (PTA2017-13681-I). E.L. thanks the Comunidad de Madrid grant Atracción de Talento 2019-T1/IND-16384.