On‐Surface Synthesis and Characterization of Triply Fused Porphyrin–Graphene Nanoribbon Hybrids

Abstract

On‐surface synthesis offers a versatile approach to prepare novel carbon‐based nanostructures that cannot be obtained by conventional solution chemistry. Graphene nanoribbons (GNRs) have potential for a variety of applications. A key issue for their application in molecular electronics is in the fine‐tuning of their electronic properties through structural modifications, such as heteroatom doping or the incorporation of non‐benzenoid rings. In this context, the covalent fusion of GNRs and porphyrins (Pors) is a highly appealing strategy. Herein we present the selective on‐surface synthesis of a Por–GNR hybrid, which consists of two Pors connected by a short GNR segment. The atomically precise structure of the Por–GNR hybrid has been characterized by bond‐resolved scanning tunneling microscopy (STM) and noncontact atomic force microscopy (nc‐AFM). The electronic properties have been investigated by scanning tunneling spectroscopy (STS), in combination with DFT calculations, which reveals a low electronic gap of 0.4 eV.

Inducing Open-Shell Character in Porphyrins through Surface-Assisted Phenalenyl π-Extension

“…On the other hand, samples with deposited precursors Por(dmp)2 and Por(dmp)4 were annealed above 300 ºC to promote the surface-assisted cyclodehydrogenation between the methyl groups and the macrocycle, giving PorA2 and PorA4, respectively. 63 The corresponding large-scale STM images of PorA2 and PorA4 confirm the presence of individual molecules, but also reveal several side-products, which are tentatively identified as covalently-linked dimers and trimers (Figure 2d,g). High-resolution STM images (Figure 2b,e,h) reveal fully planarized structures with the expected symmetry (i.e., D4h for PorA0 and PorA4, and D2h for PorA2), suggesting the successful formation of the target structures.…”

“…61 On-surface fabrication of π-extended Pors by fusing the macrocycle with PAHs has only recently been reported. 57,62,63 However, the few reported examples involve hybrids of Por with nanographenes, not focusing on the possible open-shell character of the π-system.…”

On-surface synthesis of singly and doubly porphyrin-capped graphene nanoribbon segments

“…It has been reported that p-extended Pors, Por-7AGNR hybrids, and the 7AGNR end states tend to be positively charged by the Au(111) surface. 39,43,44,46 To estimate the effect of possible interactions between the molecule and the underlying substrate, the neutral, monocationic, and dicationic GNR-Por 1(Zn) 2 hybrids were simulated. For the dicationic species, an excellent matching between the simulated LDOS maps and the experimental dI/dV maps was found ( Fig.…”

Oxidative Cyclodehydrogenation Reactions with Tetraarylporphyrins

“…[ 1–3 ] The extension of the chromophores' π‐system represents an efficient tool to alter and therefore tailor the optical properties, e.g., the position of the absorption bands. For that, small polycyclic aromatic hydrocarbons (PAHs) such as benzene [ 4–11 ] or anthracene [ 12–15 ] but also larger ones such as nanographenes [ 16,17 ] or graphene itself [ 18 ] were fused once or several times to porphyrins. Typical synthesis procedures either use already π‐extended pyrrole building blocks for porphyrin synthesis or fuse the desired aromatic units to pre‐formed porphyrins afterwards.…”