Pyrene-Fused <i>s</i>‑Indacene

One antiaromatic polycyclic hydrocarbon (PH) with and without solubilizing <i>tert</i>-butyl substituents, namely <i>s</i>-indaceno­[2,1-<i>a</i>:6,5-<i>a</i>′]­dipyrene (IDPs), has been synthesized by a four-step protocol. The IDPs represent the longitudinal, <i>peri</i>-extension of the indeno­[1,2-<i>b</i>]­fluorene skeleton towards a planar 40 π-electron system. Their structures were unambiguously confirmed by X-ray crystallographic analysis. The optoelectronic properties were studied by UV/vis absorption spectroscopy and cyclic voltammetry. These studies revealed that <i>peri</i>-fusion renders the IDP derivatives with a narrow optical energy gap of 1.8 eV. The maximum absorption of IDPs is shifted by 160 nm compared to the parent indenofluorene. Two quasi-reversible oxidation as well as reduction steps indicate an excellent redox behavior attributed to the antiaromatic core. Formation of the radical cation and the dication was monitored by UV/vis absorption spectroscopy during titration experiments. Notably, the fusion of <i>s</i>-indacene with two pyrene moieties lead to IDPs with absorption maxima approaching the near infrared (NIR) regime

Pyrene-Fused <i>s</i>‑Indacene

One antiaromatic polycyclic hydrocarbon (PH) with and without solubilizing <i>tert</i>-butyl substituents, namely <i>s</i>-indaceno­[2,1-<i>a</i>:6,5-<i>a</i>′]­dipyrene (IDPs), has been synthesized by a four-step protocol. The IDPs represent the longitudinal, <i>peri</i>-extension of the indeno­[1,2-<i>b</i>]­fluorene skeleton towards a planar 40 π-electron system. Their structures were unambiguously confirmed by X-ray crystallographic analysis. The optoelectronic properties were studied by UV/vis absorption spectroscopy and cyclic voltammetry. These studies revealed that <i>peri</i>-fusion renders the IDP derivatives with a narrow optical energy gap of 1.8 eV. The maximum absorption of IDPs is shifted by 160 nm compared to the parent indenofluorene. Two quasi-reversible oxidation as well as reduction steps indicate an excellent redox behavior attributed to the antiaromatic core. Formation of the radical cation and the dication was monitored by UV/vis absorption spectroscopy during titration experiments. Notably, the fusion of <i>s</i>-indacene with two pyrene moieties lead to IDPs with absorption maxima approaching the near infrared (NIR) regime

Unexpected Scholl Reaction of 6,7,13,14-Tetraarylbenzo[<i>k</i>]tetraphene: Selective Formation of Five-Membered Rings in Polycyclic Aromatic Hydrocarbons

Cyclodehydrogenation is a versatile reaction that has enabled the syntheses of numerous polycyclic aromatic hydrocarbons (PAHs). We now describe a unique Scholl reaction of 6,7,13,14-tetraarylbenzo­[<i>k</i>]­tetraphene, which “unexpectedly” forms five-membered rings accompanying highly selective 1,2-shift of aryl groups. The geometric and optoelectronic nature of the resulting bistetracene analogue with five-membered rings is comprehensively investigated by single-crystal X-ray, NMR, UV–vis absorption, and cyclic voltammetry analyses. Furthermore, a possible mechanism is proposed to account for the selective five-membered-ring formation with the rearrangement of the aryl groups, which can be rationalized by density functional theory (DFT) calculations. The theoretical results suggest that the formation of the bistetracene analogue with five-membered rings is kinetically controlled while an “expected” product with six-membered rings is thermodynamically more favored. These experimental and theoretical results provide further insights into the still controversial mechanism of the Scholl reaction as well as open up an unprecedented entry to extend the variety of PAHs by programing otherwise unpredictable rearrangements during the Scholl reaction

Fused Dibenzo[<i>a</i>,<i>m</i>]rubicene: A New Bowl-Shaped Subunit of C₇₀ Containing Two Pentagons

Total synthetic approaches of fullerenes are the holy grail for organic chemistry. So far, the main attempts have focused on the synthesis of the buckminsterfullerene C₆₀. In contrast, access to subunits of the homologue C₇₀ remains challenging. Here, we demonstrate an efficient bottom-up strategy toward a novel bowl-shaped polycyclic aromatic hydrocarbons (PAH) C34 with two pentagons. This PAH represents a subunit for C₇₀ and of other higher fullerenes. The bowl-shaped structure was unambiguously determined by X-ray crystallography. A bowl-to-bowl inversion for a C₇₀ fragment in solution was investigated by dynamic NMR analysis, showing a bowl-to-bowl inversion energy (Δ<i>G</i>^⧧) of 16.7 kcal mol^–1, which is further corroborated by DFT calculations

On-Surface Cyclization of <i>ortho</i>-Dihalotetracenes to Four- and Six-Membered Rings

We report on the surface-catalyzed formal [2+2] and [2+2+2] cycloadditions of <i>ortho</i>-activated tetracene species on a Ag(111) substrate under ultrahigh vacuum conditions. Three different products are obtained: tetracene dimers, trimers, and tetramers. The former results from the formation of a four-membered ring while the other two arise from cyclization into six-membered rings. These on-surface reactions have been monitored by scanning tunneling microscopy and rationalized by density functional theory calculations. Our approach, based on the reaction of <i>ortho</i>-dihalo precursor monomers via formal cycloadditions, establishes an additional method for the highly active field of on-surface synthesis and enables the development of novel 1D and 2D covalent carbon nanostructures

Toward Full Zigzag-Edged Nanographenes: <i>peri</i>-Tetracene and Its Corresponding Circumanthracene

Zigzag-edged nanographene with two rows of fused linear acenes, called as n-<i>peri</i>-acene (n-PA), is considered as a potential building unit in the arena of organic electronics. n-PAs with four (<i>peri</i>-tetracene, <b>4-PA</b>), five (<i>peri</i>-pentacene, <b>5-PA</b>) or more benzene rings in a row have been predicted to show open-shell character, which would be attractive for the development of unprecedented molecular spintronics. However, solution-based synthesis of open-shell n-PA has thus far not been successful because of the poor chemical stability. Herein we demonstrated the synthesis and characterization of the hitherto unknown <b>4-PA</b> by a rational strategy in which steric protection of the zigzag edges playing a pivotal role. The obtained <b>4-PA</b> possesses a singlet biradical character (<i>y</i>₀ = 72%) and exhibits remarkable persistent stability with a half-life time (<i>t</i>_1/2) of ∼3 h under ambient conditions. UV–vis–NIR and electrochemical measurements reveal a narrow optical/electrochemical energy gap (1.11 eV) for <b>4-PA</b>. Moreover, the bay regions of <b>4-PA</b> enable the efficient 2-fold Diels–Alder reaction, yielding a novel full zigzag-edged circumanthracene

Toward Full Zigzag-Edged Nanographenes: <i>peri</i>-Tetracene and Its Corresponding Circumanthracene

Zigzag-edged nanographene with two rows of fused linear acenes, called as n-<i>peri</i>-acene (n-PA), is considered as a potential building unit in the arena of organic electronics. n-PAs with four (<i>peri</i>-tetracene, <b>4-PA</b>), five (<i>peri</i>-pentacene, <b>5-PA</b>) or more benzene rings in a row have been predicted to show open-shell character, which would be attractive for the development of unprecedented molecular spintronics. However, solution-based synthesis of open-shell n-PA has thus far not been successful because of the poor chemical stability. Herein we demonstrated the synthesis and characterization of the hitherto unknown <b>4-PA</b> by a rational strategy in which steric protection of the zigzag edges playing a pivotal role. The obtained <b>4-PA</b> possesses a singlet biradical character (<i>y</i>₀ = 72%) and exhibits remarkable persistent stability with a half-life time (<i>t</i>_1/2) of ∼3 h under ambient conditions. UV–vis–NIR and electrochemical measurements reveal a narrow optical/electrochemical energy gap (1.11 eV) for <b>4-PA</b>. Moreover, the bay regions of <b>4-PA</b> enable the efficient 2-fold Diels–Alder reaction, yielding a novel full zigzag-edged circumanthracene

π‑Extended and Curved Antiaromatic Polycyclic Hydrocarbons

Synthesis of antiaromatic polycyclic hydrocarbons (PHs) is challenging because the high energy of their highest occupied molecular orbital and low energy of their lowest unoccupied molecular orbital cause them to be reactive and unstable. In this work, two large antiaromatic acene analogues, namely, cyclopenta­[<i>pqr</i>]­indeno­[2,1,7-<i>ijk</i>]­tetraphene (CIT, <b>1a</b>) and cyclopenta­[<i>pqr</i>]­indeno­[7,1,2-<i>cde</i>]­picene (CIP, <b>1b</b>), as well as a curved antiaromatic molecule with 48 π-electrons, dibenzo­[<i>a</i>,<i>c</i>]­diindeno­[7,1,2-<i>fgh</i>:7′,1′,2′-<i>mno</i>]­phenanthro­[9,10-<i>k</i>]­tetraphene (DPT, <b>1c</b>), are synthesized on the basis of the corona of indeno­[1,2-<i>b</i>]­fluorene. These three antiaromatic PHs possess a narrow energy gap down to 1.55 eV and exhibit high kinetic stability under ambient conditions. Moreover, these compounds display reversible electron transfer processes in both the cathodic and anodic regimes. Their cation and anion radicals are characterized by in situ vis–NIR absorption and electron paramagnetic resonance spectroelectrochemistry. The X-ray crystallographic analysis confirms that while CIP and CIT manifest planar structures, DPT shows a curved π-conjugated carbon skeleton. The synthetic strategy starting from <i>ortho</i>-substituted benzene units to construct five-membered rings in this work provides a unique entry to novel pentagon-embedding or curved antiaromatic polycyclic hydrocarbons. In addition, besides the detailed chemical and physical investigations, microscale single-crystal fiber field-effect transistors were also fabricated

Toward Full Zigzag-Edged Nanographenes: <i>peri</i>-Tetracene and Its Corresponding Circumanthracene

Zigzag-edged nanographene with two rows of fused linear acenes, called as n-<i>peri</i>-acene (n-PA), is considered as a potential building unit in the arena of organic electronics. n-PAs with four (<i>peri</i>-tetracene, <b>4-PA</b>), five (<i>peri</i>-pentacene, <b>5-PA</b>) or more benzene rings in a row have been predicted to show open-shell character, which would be attractive for the development of unprecedented molecular spintronics. However, solution-based synthesis of open-shell n-PA has thus far not been successful because of the poor chemical stability. Herein we demonstrated the synthesis and characterization of the hitherto unknown <b>4-PA</b> by a rational strategy in which steric protection of the zigzag edges playing a pivotal role. The obtained <b>4-PA</b> possesses a singlet biradical character (<i>y</i>₀ = 72%) and exhibits remarkable persistent stability with a half-life time (<i>t</i>_1/2) of ∼3 h under ambient conditions. UV–vis–NIR and electrochemical measurements reveal a narrow optical/electrochemical energy gap (1.11 eV) for <b>4-PA</b>. Moreover, the bay regions of <b>4-PA</b> enable the efficient 2-fold Diels–Alder reaction, yielding a novel full zigzag-edged circumanthracene

Supplementary Materials

This is the Supplementary Information for the paper of "Making China’s water data accessible, usable and shareable"</p