The effectiveness of five different anchor groups for non-covalent interfacing to graphene electrodes are compared. A family of six molecules is tested in single-molecule junctions: five consist of the same porphyrin core with different anchor groups, and the sixth is a reference molecule without anchor groups. The junction formation probability (JFP) has a strong dependence on the anchor group. Larger anchors give higher binding energies to the graphene surface, correlating with higher JFPs. The best anchor groups tested are 1,3,8-tridodecyloxypyrene and 2,5,8,11,14-pentadodecylhexa-peri-hexabenzocoronene, with JFPs of 36% and 38%, respectively. Many junctions are tested at 77 K for each molecule by measuring source-drain current as a function of bias and gate voltage. For each compound, there is wide variation in the strength of the electronic coupling to the electrodes and in the location of Coulomb peaks. In most cases, this device-to-device variability makes it impossible to observe trends between the anchor and the charge-transport characteristics. Tetrabenzofluorene anchors, which are not π-conjugated with the

The Diels-Alder reaction has been widely employed in synthetic organic chemistry since its discovery in 1928. The catalyst-free nature, functional group tolerance and high efficiency of the Diels-Alder reaction make it also promising for the fabrication of functional polymeric materials. In particular, a large variety of functional polyphenylenes (polymer structures mainly consisting of phenylenes) and ladderpolymers (double stranded polymers with periodic linkages connecting the strands) have been achieved by this method, showing potential applications such as polymer electrolyte membranes and gas separation. More recently, tailor-made polyphenylenes prepared by Diels-Alder polymerization have been utilized as precursors of structurally well-defined graphene nanoribbons (ribbon-shaped nanometer-wide graphene segments) with different widths, demonstrating large length (>600 nm) and tunable electronic band gaps. This article provides a comprehensive review for the use of Diels-Alder polymerization to build functional polyphenylenes, ladder-polymers and graphene nanoribbons.

Edge functionalization of bottom-up synthesized graphene nanoribbons (GNRs) with anthraquinone and naphthalene/perylene monoimide units has been achieved through a Suzuki coupling of polyphenylene precursors bearing bromo groups, prior to the intramolecular oxidative cyclo-dehydrogenation. High efficiency of the substitution has been validated by MALDI-TOF MS analysis of the functionalized precursors and FT-IR, Raman, and XPS analyses of the resulting GNRs. Moreover, AFM measurements demonstrated the modulation of the self-assembling behavior of the edge-functionalized GNRs, revealing that GNR-PMI formed an intriguing rectangular network. This result suggests the possibility of programming the supramolecular architecture of GNRs by tuning the functional units.

Multiple fused pentagon−heptagon pairs are frequently found as defects at the grain boundaries of the hexagonal graphene lattice and are suggested to have a fundamental influence on graphene-related materials. However, the construction of sp 2carbon skeletons with multiple regularly fused pentagon−heptagon pairs is challenging. In this work, we found that the pentagon− heptagon skeleton of azulene was rearranged during the thermal reaction of an azulene-incorporated organometallic polymer on Au(111). The resulting sp 2 -carbon frameworks were characterized by high-resolution scanning probe microscopy techniques and feature novel polycyclic architectures composed of multiple regularly fused pentagon−heptagon pairs. Moreover, the calculated analysis of its aromaticity revealed a peculiar polar electronic structure.

Proton-responsive photochromic molecules are attractive for their ability to react on non-invasive rapid optical stimuli and the importance of protonation/deprotonation processes in various fields. Conventionally, their acidic/basic sites are on hetero-atoms, which are orthogonal to the photoactive p-center. Here, we incorporate azulene, an acid-sensitive pure hydrocarbon, into the skeleton of a diarylethene-type photoswitch. The latter exhibits a novel proton-gated negative photochromic ring-closure and its optical response upon protonation in both open and closed forms is much more pronounced than those of diarylethene photoswitches with hetero-atom based acidic/basic moieties. The unique behavior of the new photoswitch can be attributed to direct protonation on its p-system, supported by 1 H NMR and theoretical calculations. Our results demonstrate the great potential of integrating non-alternant hydrocarbons into photochromic systems for the development of multi-responsive molecular switches.

These authors contributed equally to this work.ABSTRACT: Azulene, the smallest neutral non-alternant aromatic hydrocarbon, serves not only as a prototype for fundamental studies but also a versatile building block for functional materials because of its unique (opto)electronic properties. In this work, we report the on-surface synthesis and characterization of the homopolymer of azulene connected exclusively at the 2,6-positions, namely 2,6-polyazulene, using 2,6-diiodoazulene as the monomer precursor. As an intermediate to the formation of polyazulene, a gold-(2,6-azulenylene) chain is observed. The structural details of the resulting 2,6-polyazulene are resolved by high-resolution scanning probe methods, and the electronic properties characterized by scanning tunneling spectroscopy in combination with density functional theory calculations, revealing n-type semiconducting character. Our results provide a route toward the synthesis of novel azulene-based nanostructures, of fundamental interest but difficult to be achieved by conventional solution chemistry.Properties of carbon-based aromatic systems are sensitively determined by their bond topologies. 1,2 So far, much attention has been paid to the design and synthesis of aromatic materials like conjugated polymers and nanographenes constituted by alternant hydrocarbons, which do not possess oddmembered rings. In contrast, incorporation of non-alternant hydrocarbons has only rarely been explored. Electronic and optical properties of alternant and non-alternant hydrocarbons differ profoundly.3 Azulene (Scheme 1), for example, an aromatic hydrocarbon containing 10 π-electrons, has several characteristics that differ from its isomer naphthalene. 4,5 Azulene has an intrinsic dipole

Dimeric aminoazulene and poly[2(6)-aminoazulene] are synthesized by Buchwald–Hartwig coupling of the corresponding monomeric carbamatoaminozulenes followed by hydrolysis.

Achieving exquisite control over self-assembly of functional polycyclic aromatic hydrocarbons (PAH) and nanographene (NG) is essential for their exploitation as active elements in (nano)­technological applications. In the framework of our effort to leverage their functional complexity, we designed and synthesized two hexa-peri-hexabenzocoronene (HBC) triads, p AHA and o AHA, decorated with two light-responsive azobenzene moieties at the pseudo-para and ortho positions, respectively. Their photoisomerization in solution is demonstrated by UV–vis absorption. 1H NMR measurements of o AHA suggested 23% of Z-form can be obtained at a photostationary state with UV irradiation (366 nm). Scanning tunneling microscopy imaging revealed that the self-assembly of p AHA and o AHA at the solid–liquid interface between highly oriented pyrolytic graphite (HOPG) and their solution in 1,2,4-trichlorobenzene can be modulated upon light irradiation. This is in contrast to our previous work using HBC bearing a single azobenzene moiety, which did not show such photomodulation of the self-assembled structure. Upon E-Z isomerization both p AHA and o AHA displayed an increased packing density on the surface of graphite. Moreover, p AHA revealed a change of self-assembled pattern from an oblique unit cell to a dimer row rectangular crystal lattice whereas the assembly of o AHA retained a dimer row structure before and after light irradiation, yet with a modification of the inter-row molecular orientation. Molecular mechanics/molecular dynamics simulations validated the self-assembly patterns of p AHA and o AHA, comprising azobenzenes in their Z-forms. These results pave the way toward use of suitably functionalized large PAHs, as well as NGs, to develop photoswitchable devices.