B₂N₂‑Dibenzo[<i>a</i>,<i>e</i>]pentalenes: Effect of the BN Orientation Pattern on Antiaromaticity and Optoelectronic Properties

Two BN units were embedded in dibenzo­[<i>a</i>,<i>e</i>]­pentalene with different orientation patterns, which significantly modulated its antiaromaticity and optoelectronic properties. Importantly, the vital role of the BN orientation in conjugated molecules with more than one BN unit was demonstrated for the first time. This work indicates a large potential of the BN/CC isosterism for the development of new antiaromatic systems and highlights the importance of precise control of the BN substitution patterns in conjugated materials

Synthesis of Stable Nanographenes with OBO-Doped Zigzag Edges Based on Tandem Demethylation-Electrophilic Borylation

A tandem demethylation-aryl borylation strategy was developed to synthesize OBO-doped tetrabenzo­[<i>a,f,j,o</i>]­perylenes (namely “bistetracenes”) and tetrabenzo­[<i>bc,ef,kl,no</i>]­coronenes (namely “peritetracenes”). The OBO-doped bistetracene analogues exhibited excellent stability and strong fluorescence, in contrast to the unstable all-carbon bistetracene. Single-crystal X-ray analysis for OBO-doped bistetracene revealed a twisted double [5]­helicene structure, indicating that this synthesis is applicable to new heterohelicenes. Importantly, cyclodehydrogenation of the bistetracene analogues successfully produced the unprecedented heteroatom-doped peritetracenes, which opened up a new avenue to periacene-type nanographenes with stable zigzag edges

Synthesis of Stable Nanographenes with OBO-Doped Zigzag Edges Based on Tandem Demethylation-Electrophilic Borylation

A tandem demethylation-aryl borylation strategy was developed to synthesize OBO-doped tetrabenzo­[<i>a,f,j,o</i>]­perylenes (namely “bistetracenes”) and tetrabenzo­[<i>bc,ef,kl,no</i>]­coronenes (namely “peritetracenes”). The OBO-doped bistetracene analogues exhibited excellent stability and strong fluorescence, in contrast to the unstable all-carbon bistetracene. Single-crystal X-ray analysis for OBO-doped bistetracene revealed a twisted double [5]­helicene structure, indicating that this synthesis is applicable to new heterohelicenes. Importantly, cyclodehydrogenation of the bistetracene analogues successfully produced the unprecedented heteroatom-doped peritetracenes, which opened up a new avenue to periacene-type nanographenes with stable zigzag edges

Fusion at the Non-K-Region of Pyrene: An Alternative Strategy To Extend the π‑Conjugated Plane of Pyrene

A large fused pyrene derivative <b>TTTP</b> was facilely developed through fusion at the non-K-region of pyrene, which represents the first example of extending such a π-conjugated plane at its non-K-region. The investigation of its photophysical properties and other characterizations indicated that <b>TTTP</b> exhibited strong aggregation behaviors and self-assembled into highly ordered one-dimensional nanowires due to its large π-conjugated plane

Synthesis, Structure, and Chiroptical Properties of a Double [7]Heterohelicene

The synthesis of 11a,25a-dibora-11,­12,­25,­26-tetraoxatetranaphtho­[1,2-<i>a</i>:2′,1′-<i>f</i>:1″,2″-<i>j</i>:2‴,1‴-<i>o</i>]­perylene, a double [7]­heterohelicene containing OBO units, has been achieved via tandem demethylation-borylation, representing the highest double helicene reported thus far with all six-membered rings. Single-crystal X-ray analysis clearly demonstrated a significantly twisted structure with the terminal aromatic rings overlapping at both ends, giving the first example of a double helicene with intramolecular π-layers. Such structural features resulted in a high theoretical isomerization barrier of 45.1 kcal/mol, which is the highest value for all the double helicenes ever reported, rendering the achieved molecule with high chiral stability. The (<i>P</i>,<i>P</i>)- and (<i>M</i>,<i>M</i>)-isomers were separated by chiral HPLC and the chiroptical properties were investigated, revealing opposite circular dichroism responses

Fused Bis-Benzothiadiazoles as Electron Acceptors

Fused bis-benzothiadiazoles with different molecular geometries, namely, linear benzoquinone-fused bis­(benzothiadiazole) (Q-BBT) and V-shaped sulfone-fused bis­(benzothiadiazole) (S-BBT), were synthesized. Single crystal analysis of Q-BBT and S-BBT revealed profoundly distinct packing modes, which must be ascribed to the different molecular shapes. Experimental and theoretical studies indicated that both compounds give rise to electron-accepting materials. This work thus also contributes to the diversity of electron acceptors based on bis-benzothiadiazole moieties and highlights the important role of molecular shape for the solid-state packing of organic conjugated materials

A Straightforward Strategy toward Large BN-Embedded π‑Systems: Synthesis, Structure, and Optoelectronic Properties of Extended BN Heterosuperbenzenes

A straightforward strategy has been used to construct large BN-embedded π-systems simply from azaacenes. BN heterosuperbenzene derivatives, the largest BN heteroaromatics to date, have been synthesized in three steps. The molecules exhibit curved π-surfaces, showing two different conformations which are self-organized into a sandwich structure and further packed into a π-stacking column. The assembled microribbons exhibit good charge transport properties and photoconductivity, representing an important step toward the optoelectronic applications of BN-embedded aromatics

Epindolidione-Based Conjugated Polymers: Synthesis, Electronic Structures, and Charge Transport Properties

Development of new electron-deficient building blocks is essential to donor–acceptor conjugated polymers. Herein, epindolidione (EPD) as electron-deficient unit was integrated into conjugated polymers for the investigation of field-effect transistors for the first time. We systematically studied the electronic structures and charge transport properties of the EPD-based donor–acceptor polymers. They exhibit <i>p</i>-type transport characteristics with the highest mobility of up to 0.40 cm² V^–1 s^–1, thus demonstrating its great potential as a building block for polymer field-effect transistors and photovoltaics

Impacts of Stereoisomerism on Molecular Packing and Charge Transport of Imide-Fused Corannulene Derivatives

Two chiral tertiary carbon centers bearing one mesityl group at each center are introduced into the molecular backbone of imide-fused corannulene derivatives to produce four stereoisomers (i.e., (<i>S</i>, <i>S</i>), (<i>R</i>, <i>R</i>), (<i>R</i>, <i>S</i>), or (<i>S</i>, <i>R</i>) configurations on two chiral carbons) in one pot, which are separated into two portions through column chromatography over silica gel. Portion 1, containing a pair of enantiomers ((<i>S</i>, <i>S</i>) and (<i>R</i>, <i>R</i>)), adopts layered packing in the crystal. Portion 2, consisting of a pair of mesomers ((<i>R</i>, <i>S</i>) and (<i>S</i>, <i>R</i>)), exhibits columnar packing in their cocrystal. Theoretical calculations are performed on these two packing motifs, revealing that Portion 1 displays hole-dominated transport, whereas Portion 2 shows electron-dominated transport

Monitoring the On-Surface Synthesis of Graphene Nanoribbons by Mass Spectrometry

We present a mass spectrometric approach to characterize and monitor the intermediates of graphene nanoribbon (GNR) formation by chemical vapor deposition (CVD) on top of Au(111) surfaces. Information regarding the repeating units, lengths, and termini can be obtained directly from the surface sample by a modified matrix-assisted laser desorption/ionization (MALDI) method. The mass spectrometric results reveal ample oxidative side reactions under CVD conditions that can be drastically diminished by the introduction of protective H₂ gas at ambient pressure. Simultaneously, the addition of hydrogen extends the lengths of the oligophenylenes and thus the final GNRs. Moreover, the prematurely formed cyclodehydrogenation products during the oligomer growth can be assigned by the mass spectrometric technique. The obtained mechanistic insights provide valuable information for optimizing and upscaling the bottom-up fabrication of GNRs. Given the important role of GNRs as semiconductors, the mass spectrometric analysis provides a readily available tool to characterize and improve their structural perfection