Undecabenzo[7]superhelicene: a helical nanographene ribbon as CPL emitter

We report the synthesis and characterization of an enantiopure superhelicene nanographene constituted by two saddleshaped and one planar hexabenzocoronene (HBC) units arranged in a helicoidal shape. This is, to the best of our knowledge, the first undecabenzo[7]carbohelicene, i.e., the first fully π-extended [7]helicene. Racemic resolution allowed its chiroptical properties analysis revealing dissymmetry factors in the range of 2×10-3 both in the absorption and in the emission measurements. Remarkably, nonlinear photophysical analysis showed two-photon absorption crosssection of 870 GM at 800 nm and a perfect overlapping between linear, non-linear and chiral emission.-European Research Council (ERC-2015-STG-677023) -Ministerio de Economía y Competitividad (MINECO, Spain): CTQ2015-70283-P -Fundacao para a Ciencia e a tecnologia, Portugal: UID/NAN/50024/2013, IF/00759/2013 -Universidad de Granad

A triskelion-shaped saddle-helix hybrid nanographene

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 emissionWe 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

Conductance and application of organic molecule pairs as nanofuses

We propose that a pair of organic molecules can mimic the behavior of a macroscopic fuse at nanoscale, one component of the pair being the on state and the other the off state. For this task wemake use of density-functional theory to calculate the physical properties of selected molecules, which have also been synthesized by our team. By this means we obtain the transmission spectra and the current of the proposed devices, which allows us to compare the behavior of the on and off states.Of particular interest is the on/off switch ratios, defined as the current ratios of the on and off structures at the corresponding bias voltage. In a first stage, we examine the best linker between the device and the electrode for high on/off switch ratios. Once this is determined, we test the influence of the electron richness of the system to provide a high on/off switch ratio. The entire analysis is also supported by the molecular projected self-consistent Hamiltonian, which provides a good way of understanding the molecular behavior. All the calculations support that interesting on/off switch ratios of two orders of magnitude could be obtained with these prototypical nanofusesWe thank the Regional Government of Andalucía for financial support (Projects No. P06-FQM-01726 and No. P09-FQM-04571), the “Centro de Supercomputación de la Universidad de Granada,” and the “Centro de Computación Científica-UAM” for computation time. The authors are also grateful to the Spanish Secretaría de Estado de Universidades e Investigación, Ministerio de Educación y Ciencia, for financial support within research projects TEC2007-66812 and TEC2010-16211. N.F. thanks the Regional Government of Andalucía for her research contract, and LAC thanks the University of Granada for his research contrac

2D self-assembly of o-OPE foldamers for chiroptical barcoding

We report on the preparation and characterization of two dimensional (2D) films of (S,S,P)-1 and (R,R,M)-1ortho-oligophenylene ethylene (o-OPE) enantiomers presenting high values of circularly polarized luminescence (CPL). The amphiphilic character of these two molecules allows a precise 2D self-assembly at the air/water interface and an efficient transfer onto a glass solid support. The morphological and chiroptical characterization of the solid supports after the transfer of 1, 8, 16 and 32 Langmuir films of (S,S,P)-1 and (R,R,M)-1 has been carried out. The strong chiroptical values of these monomers allow reliable ECD measurements to be obtained after a single transfer, with ECD values increasing as the number of transferred films increases. The semi-liquid behavior of the monomers on the solid substrate allows CPL measurements free of photoselection artifacts that show values similar to those obtained in solution and independent of monomer concentration. All these properties have allowed us to develop the first simple organic molecule (SOM)-based chiroptical barcoding presenting positive and negative regions as a proof of concept

Unravelling the 2D self-assembly of Fmoc-dipeptides at fluid interfaces

Dipeptides self-assemble into supramolecular structures showing plenty of applications in the nanotechnology and biomedical fields. A set of Fmoc-dipeptides with different aminoacid sequences has been synthesized and their self-assembly at fluid interfaces has been assessed. The relevant molecular parameters for achieving an efficient 2D self-assembly process have been established. The selfassembled nanostructures of Fmoc-dipeptides displayed significant chirality and retained the chemical functionality of the aminoacids. The impact of the sequence on the final supramolecular structure has been evaluated in detail using in situ characterization techniques at air/water interfaces. This study provides a general route for the 2D self-assembly of Fmoc-dipeptides

Enantiopure double ortho-oligophenylethynylene-based helical structures with circularly polarized luminescence activity

In this paper, we describe the optical and chiroptical properties of an enantiopure multipodal ortho-oligophenylethynylene (S,S,S,S)-1 presenting four chiral sulfoxide groups at the extremes. The presence of these groups together with alkynes allows the coordination with carbophilic Ag(I), and/or oxophilic Zn(II) cations, yielding double helical structures in an enantiopure way. In this sense, different behaviors in absorption, fluorescence, ECD and CPL spectra have been found depending on the stoichiometry and nature of the metal. We have observed that Zn(II) coordination favors an intensity increase of the electronic circular dichroism (ECD) spectra of compound (S,S,S,S)-1 yielding an M-helicity in the ortho-oligophenylene ethynylene (o-OPE) backbone. On the other hand, ECD spectra of final Ag(I) complex shows two different bands with an opposite sign to the free ligand, thus giving the P-helical isomer. In addition, circularly polarized luminescence (CPL) exhibit an enhanced intensity and negative sign in both complexes. Computational studies were also carried out, supporting the experimental result

Chiral Single-Molecule Potentiometers Based on Stapled ortho- Oligo(phenylene)ethynylenes

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

Two-dimensional carbon-based conductive materials with dynamically controlled asymmetric Dirac cones

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 literatureWe 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 contract

Novel ortho-OPE metallofoldamers: binding-induced folding promoted by nucleating Ag(i)-alkyne interactions

We have developed a new family of ortho-oligophenylene ethynylene (o-OPE) metallofoldamers. The folding of these helicates is induced by nucleating carbon-metal interactions between Ag(i) cations and the alkynes of the inner core of the o-OPEs. These o-OPEs form metal-organic assemblies where at least three alkyne moieties are held in close proximity to form novel Ag(i)-complexes with the metal ion lodged into the helical cavity. NMR titration experiments and photokinetic studies have provided quantitative data about the thermodynamic and kinetic features of such binding/folding phenomena. X-ray diffraction and DFT studies have been performed to extract structural information on how the Ag(i) cation is accommodated into the cavity. The great simplicity and versatility of these new metallofoldamers open up the possibility to develop novel structures with applications in material science and/or in asymmetric catalysisThis research was funded by the Regional Government of Andalucía (project P09-FQM-4571) and the ICIQ Foundation. DM thanks Regional Government of Andalucía for her contract. AML thanks MICINN for her FPU fellowship. The authors thank the Centro de Servicios de Informática y Redes de Comunicaciones (CSIRC), Universidad de Granada, for providing the computing tim

On-Surface Thermal Stability of a Graphenic Structure Incorporating a Tropone Moiety

On-surface synthesis, complementary to wet chemistry, has been demonstrated to be a valid approach for the synthesis of tailored graphenic nanostructures with atomic precision. Among the different existing strategies used to tune the optoelectronic and magnetic properties of these nanostructures, the introduction of non-hexagonal rings inducing out-of-plane distortions is a promising pathway that has been scarcely explored on surfaces. Here, we demonstrate that non-hexagonal rings, in the form of tropone (cycloheptatrienone) moieties, are thermally transformed into phenyl or cyclopentadienone moieties upon an unprecedented surface-mediated retro–Buchner-type reaction involving a decarbonylation or an intramolecular rearrangement of the CO unit, respectivel