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.