Tetrabenzoperipentacene: Stable Five-Electron Donating Ability and a Discrete Triple-Layered β-Graphite Form in the Solid State

Synthesis of Hetero-Trimetal Porphyrin Nanobelts

This work reported "trinitarian" porphyrin nanobelts, contained hetero-trimetal ions. The high-resolution mass spectrometry and X-ray crystallography proved PNBNiCuPd consisting of three different bent porphyrin(2.1.2.1) metal complex moieties. The redox properties indicate porphyrin nanobelts demonstrate the multielectron donating and accepting properties, more than nine redox processes.

Peri-pentacene and Peri-hexacene Diradicaloids

Peri-acenes are valuable models for zigzag-edged graphene nanoribbons, but their synthesis poses significant challenges. In this study, stable derivatives of peri-pentacene (Peri-P) and peri-hexacene (Peri-H) were synthesized. Through kinetic blocking and a synergistic captodative effect, both compounds displayed remarkable stability under ambient air and light conditions. They show significant diradical character (y0), with y0 = 75.4% for Peri-P and y0 = 90.7% for Peri-H, alongside narrow singlet-triplet energy gaps of -1.68 ± 0.04 and -1.28 ± 0.02 kcal/mol, respectively. The structure of Peri-H was confirmed by X-ray crystallography, with bond-length analysis and theoretical calculations indicating a dominant structure featuring five aromatic sextet rings. Their optical and electrochemical properties were also studied and compared to those of smaller peri-acenes.

π-extended pyrenes: from an antiaromatic buckybowl to doubly curved nanocarbons with gulf architectures

The synthesis of π-extended pyrenes keeps attracting considerable attention. In particular, frameworks containing nonbenzenoid rings might display intriguing properties. Here, we report a practical synthetic pathway to access a new buckybowl (1), which is composed of four five-membered rings externally fused to a pyrene core. The buckybowl 1 exhibits antiaromaticity involving 22 π-electrons, a rapid bowl-to-bowl interconversion, and a small band gap. Furthermore, this buckybowl could be subjected to Scholl cyclodehydrogenation to prepare the doubly curved nanocarbons (2rac and 2meso), which exist as two diastereomers, as demonstrated by X-ray crystal structure determination. Variable temperature 1H NMR measurements reveal that 2meso can isomerize into 2rac under thermal conditions, with an activation free energy of 27.1 kcal mol-1. Both the enantiomers of 2rac can be separated by chiral HPLC and their chiroptical properties are thoroughly examined. In addition, the nanocarbon 2meso with two gulf architectures facilitates host-guest chemistry with a variety of guests, including PDI, TDI, C60 and C70.

N=8 Armchair Graphene Nanoribbons: Solution Synthesis and High Charge Carrier Mobility

Structurally defined graphene nanoribbons (GNRs) have emerged as promising candidates for nanoelectronic devices. Low band gap (<1 eV) GNRs are particularly important when considering the Schottky barrier in device performance. Here, we demonstrate the first solution synthesis of 8-AGNRs through a carefully designed arylated polynaphthalene precursor. The efficiency of the oxidative cyclodehydrogenation of the tailor-made polymer precursor into 8-AGNRs was validated by FT-IR, Raman, and UV/Vis-near-infrared (NIR) absorption spectroscopy, and further supported by the synthesis of naphtho[1,2,3,4-ghi]perylene derivatives (1 and 2) as subunits of 8-AGNR, with a width of 0.86 nm as suggested by the X-ray single crystal analysis. Low-temperature scanning tunneling microscopy (STM) and solid-state NMR analyses provided further structural support for 8-AGNR. The resulting 8-AGNR exhibited a remarkable NIR absorption extending up to ∼2400 nm, corresponding to an optical band gap as low as ∼0.52 eV. Moreover, optical-pump TeraHertz-probe spectroscopy revealed charge-carrier mobility in the dc limit of ∼270 cm2  V-1  s-1 for the 8-AGNR.

The Scholl Reaction as a Powerful Tool for Synthesis of Curved Polycyclic Aromatics

The past decade has witnessed remarkable success in the synthesis of curved polycyclic aromatics through Scholl reactions which enable oxidative aryl-aryl coupling even in company with the introduction of significant steric strain. These curved polycyclic aromatics are not only unique objects of structural organic chemistry in relation to the nature of aromaticity but also play an important role in bottom-up approaches to precise synthesis of nanocarbons of unique topology. Moreover, they have received considerable attention in the fields of supramolecular chemistry and organic functional materials because of their interesting properties and promising applications. Despite the great success of Scholl reactions in synthesis of curved polycyclic aromatics, the outcome of a newly designed substrate in the Scholl reaction still cannot be predicted in a generic and precise manner largely due to limited understanding on the reaction mechanism and possible rearrangement processes. This review provides an overview of Scholl reactions with a focus on their applications in synthesis of curved polycyclic aromatics with interesting structures and properties and aims to shed light on the key factors that affect Scholl reactions in synthesizing sterically strained polycyclic aromatics.

Benzo-Fused Periacenes or Double Helicenes? Different Cyclodehydrogenation Pathways on Surface and in Solution

Controlling the regioselectivity of C-H activation in unimolecular reactions is of great significance for the rational synthesis of functional graphene nanostructures, which are called nanographenes. Here, we demonstrate that the adsorption of tetranaphthyl- p-terphenyl precursors on metal surfaces can completely change the cyclodehydrogenation route and lead to obtaining planar benzo-fused perihexacenes rather than double [7]helicenes during solution synthesis. The course of the on-surface planarization reactions is monitored using scanning probe microscopy, which unambiguously reveals the formation of dibenzoperihexacenes and the structures of reaction intermediates. The regioselective planarization can be attributed to the flattened adsorption geometries and the reduced flexibility of the precursors on the surfaces, in addition to the different mechanism of the on-surface cyclodehydrogenation from that of the solution counterpart. We have further achieved the on-surface synthesis of dibenzoperioctacene by employing a tetra-anthryl- p-terphenyl precursor. The energy gaps of the new nanographenes are measured to be approximately 2.1 eV (dibenzoperihexacene) and 1.3 eV (dibenzoperioctacene) on a Au(111) surface. Our findings shed new light on the regioselectivity in cyclodehydrogenation reactions, which will be important for exploring the synthesis of unprecedented nanographenes.

X-Shaped Polycyclic Aromatic Hydrocarbons: Optical Properties and Tunable Assembly Ability

Although a number of synthetic methodologies have been developed to prepare stable polycyclic aromatic hydrocarbons (PAHs), much less research has been devoted to functionalizing the peripheries of molecules to tune the self-assembly ability or introduce functional groups without altering their photophysical properties. Herein, we report twisted "X"-shaped molecules prepared through annulation of hexacene with benzoanthracene on the zigzag edge, and an investigation of their photophysical properties and self-assembly properties. The shape-complementary "X"-shaped molecules prefer to dimerize, while the π-extension would lead to one-dimensional π-stacking. Our findings give some insights into the design of stable PAHs without disturbing the electronic structures.

A novel graphite-like stacking structure in a discrete molecule and its molecular recognition behavior

Macrocyclic imines containing two hexabenzocoronene planes adopted a unique intramolecular stacking structure, similar to the stacking pattern in natural graphite.

Azaacenes as active elements for sensing and bio applications

Recent progress in the application of azaacenes in sensing and bio-fields has been summarized.

Parent and trisubstituted triazacoronenes: synthesis, crystal structure and physicochemical properties

The parent 1,5,9-triazacoronene and its derivatives bearing various substituents were concisely synthesized, which are promising candidates for emissive and electron-transport materials.

New advances in nanographene chemistry

This review discusses recent advancements in nanographene chemistry, focusing on the bottom-up synthesis of graphene molecules and graphene nanoribbons.