The larger acenes and heteroacenes (>pentacenes) are attractive, yet sensitive materials; several strategies were developed to stabilize such species. “Classic” approaches employ bulky substituents that also solubilize these polycyclic aromatic (aza)hydrocarbons. Alternative strategies were developed conferring kinetic stabilization through solid state arrangements, addition of further Clar sextets through π-extension, on-surface syntheses and stabilization through extreme steric shielding, giving a highly twisted acene backbone. Another option is the generation of isoelectronic acene analogues from π-extended quinodimethanes. Some of the highly stabilized materials do not mimic the characteristics of their parent (aza)acenes but exhibit different – yet attractive – properties, dissected in this review.

Unusual stabilization of larger acenes and heteroacenes

Organic diradicaloids have unique open-shell structures and properties and promising applications in organic electronics and spintronics. Incorporation of heteroatoms is an effective strategy to alter the electronic structures of organic diradicaloids. However, B-containing organic diradicaloids are very challenging due to their high reactivities, which are caused by not only diradical nature but also the B atom. In this article, we report a new kind of organic diradicaloids containing boron atoms. Our strategy is to incorporate planarized triarylboranes to antiaromatic polycyclic hydrocarbons (PHs). We synthesized two isomeric B-containing PHs composed of indenofluorene π-skeletons and two dioxa-bridged triphenylborane moieties. As proved by theoretical and experimental results, both of them have excellent ambient stability and open-shell singlet diradical structures, as well as intriguing magnetic and optoelectronic properties, such as thermally accessible triplet species, reversible multiredox ability, and narrow energy gaps. Notably, they possess sufficient Lewis acidity, which has never been observed for organic diradicaloids. In addition, they can coordinate with Lewis bases to form Lewis adducts, achieving unprecedented dynamic modulations of (anti)aromaticity and thus diradical character of organic diradicaloids.

Boron-Containing Organic Diradicaloids: Dynamically Modulating Singlet Diradical Character by Lewis Acid-Base Coordination.

The uncontrollable dendrite growth of Li metal anode leads to poor cycle stability and safety concerns, hindering its utilization in high energy density batteries. Herein, a phenoxy radical Spiro-O8 is proposed as an artificial protection film for Li metal anode owing to its excellent film-forming capability and remarkable ionic conductivity. A spontaneous redox reaction between the Spiro-O8 and Li metal results in the formation of a uniform and highly ionic conductive organic film in the bottom. Meanwhile, the phenoxy radicals on surface of Spiro-O8 facilitate the decomposition of Li salt upon exposed to the ether electrolyte and lead the formation of LiF film on the top. Arising from the synergistic effects of inner high ionic conductive film and outer rigid film, stable Li plating/stripping can be realized at a high current density (4000 cycles at 10 mA cm-2 ) and a high areal capacity of 5 mAh cm-2 for 550 h with an ultrahigh Li utilization rate of 54.6 %. As a proof of concept, this work shows a facile strategy to rationally fabricate dual-layered interfaces for Li metal anodes.

Phenoxy Radical-induced Formation of Dual-Layered Protection Film for High-Rate and Dendrite-free Lithium Metal Anodes.

By stabilizing unpaired spin in the ground state, open-shell π-conjugated molecules can achieve optoelectronic properties that are inaccessible to closed-shell compounds. Here, we report the synthe...

Open-Shell Effects on Optoelectronic Properties: Antiambipolar Charge Transport and Anti-Kasha Doublet Emission from a N-Substituted Bisphenalenyl

Peroxynitrite (ONOO–) is involved in neurodegenerative, inflammatory, cardiovascular disorders, cancers, and other pathological progress. However, current imaging methods for sensing ONOO– usually ...

Oxygen-Embedded Pentacene Based Near-Infrared Chemiluminescent Nanoprobe for Highly Selective and Sensitive Visualization of Peroxynitrite In Vivo.

Extension of oxygen-embedded polycyclic aromatic hydrocarbons (PAHs), in particular with a defined topology, is synthetically challenging primarily because of limited regio-specific methods and poo...

Synthesis and Characterization of Oxygen-Embedded Quinoidal Pentacene and Nonacene

Light-operated excited-state photochemical reactions and the resulting photochromic materials have gained significant attention for their promising technological applications in molecular electronic and photonic devices. To obtain photochromic materials (e.g., diarylethenes) with desired properties, the way to tune energy processes of the excited state is essentially important, from both fundamental and practical viewpoints. The modified diarylethenes mostly focused on structural improvements to achieve efficient photochromism. We report here two new spiro-conjugated indenodiarylethenes (named, SFI-Th and SFI-Sul) with an orthogonally arranged spiro π-scaffold. The spiro fluorene sterically constrains the free volume of photoactive side aromatic rings, while the spiro-conjugation points toward modulation of the decaying channels of excited-state energy, thus allowing for tuning photochromic performances. These spirodiarylethenes SFI-Th and SFI-Sul are readily accessible with low cost and show distinct photochromic and photoluminescent properties. On one hand, the SFI-Th bearing bisthienyl side rings, is an excellent photochromic switch showing high thermal stability and high fatigue resistance in both solution and amorphous state, likely benefited from steric-induced excited-state energy transfer into reversible photochemical reactions, owing to higher π-orbital spiro-conjugation between the two molecular halves. On the other hand, the SFI-Sul with bissulfonyl side rings, most notably, displays quantitative photocyclization to yield SFI-Sulc upon excitation. However, the ring-closed SFI-Sulc has an extremely slow photocycloreversion, and meanwhile immediately switches on emissive state with a strong fluorescence (Φf=0.57 in amorphous powder state). We study the modulated roles of spiro π-scaffold in both cases computationally and experimentally, and attribute the facilitated photochemical reaction to the positively electronic effects of spiro-conjugation, and the photo-responsive radiative transition to the negatively electronic effects of spiro-conjugation, respectively. In all, this work demonstrates that the spiro-conjugation is a new and efficient strategy to deliver excitation energy transfer (EET) for featured photochromic properties, due to its advantage in steric-induced electronic modulation.

Spiro-conjugated indenodiarylethenes: enabling steric-induced electronic tuning of photochromic and photoluminescent properties by spiro-conjugation

We report an air-stable tetraradicaloid based on a rarely explored perylenequinonoid (PQ) core, namely, tetrabenzo-annulated tetracyclopenta[b,e,k,n]perylene (TBCP), which has a quadruple helical s...

https://www.chinesechemsoc.org/doi/pdf/10.31635/ccschem.021.202000658

Stable Quadruple Helical Tetraradicaloid with Thermally Induced Intramolecular Magnetic Switching

Aggregate science has led to the existence of functional properties at the aggregate level that significantly differs from those of corresponding single-molecule species, leading to a number of novel conceptual materials with state-dependent functionality. For developing such materials, new molecular scaffolds that allow modulating the structural and functional properties of aggregates in a controlled manner could be extremely helpful. In this study, we report a class of spiro-fused bicyclo[3,2,2] octatriene triptycene derivatives with a unique 3D molecular scaffolding structure that display aggregation-induced emission (AIE) activity with bright solid-state blue luminescence. The core scaffold features a Y-shaped bicyclo[3,2,2]octatriene backbone and a vertical crossover arrangement of adjacent spiro-conjugated rings. Unlike classic bicyclo[2,2,2]octatrienes with high rigidity, this stereoscopic bicyclo[3,2,2]octatriene containing a seven-membered ring allows retaining certain flexibility in the molecular scaffold, which results in a weak fluorescence in dilute solutions (ΦF < 10%). However, the corresponding molecular aggregates emit intense fluorescence (ΦF = 50%–5%) and show prominent AIE activity because of the restriction of intramolecular scaffold motions. Moreover, in principle, these stereoscopic scaffold constructions with partially restricted flexibility facilitate the assembly of multiple different crystalline packing structures in both porous and nonporous forms depending on the growth conditions of crystalline aggregates. The obtained crystals with regular voids (12.85 × 6.89 A each) show reversible luminescence in response to the adsorption/desorption of iodine vapor. These materials based on an unusual 3D scaffold exhibit a high degree of structural modulation at the aggregate level and demonstrate potential applications in chemical sensing and flexible optoelectronics, which may open up the exploration of highly stereoscopic molecular building blocks for developing functional aggregates.

Spiro-fused bicyclo[3,2,2] octatriene-cored triptycene: synthesis, molecular packing, and functional aggregates

The invention belongs to the field of photoelectric materials, and particularly discloses a dihelicene functional molecular material of X-type heterocyclic perylene aromatic hydrocarbon, as well as apreparation method and application method thereof. According to the preparation method, perylene and a conjugated system are condensed in a three-dimensional space, the dihelicene functional molecularmaterial of X-type heterocyclic perylene aromatic hydrocarbon is constructed by a heterocycle mode, the pi electron conjugated structure and physical property of a conjugated molecule are regulated,so that the dihelicene functional molecular material is a multifunctional integrated organic molecular material with solid fluorescence, charge transfer, chiral light absorption and chiral circularlypolarized luminescence. The dihelicene functional molecular material can be applied to electronic devices, chiral optical elements and the like for multifunctional materials.

Yanpei Wang

Papers

Synthesis and Characterization of Oxygen-Embedded Quinoidal Pentacene and Nonacene

Spiro-conjugated indenodiarylethenes: enabling steric-induced electronic tuning of photochromic and photoluminescent properties by spiro-conjugation

Stable Quadruple Helical Tetraradicaloid with Thermally Induced Intramolecular Magnetic Switching

Spiro-fused bicyclo[3,2,2] octatriene-cored triptycene: synthesis, molecular packing, and functional aggregates

Dihelicene functional molecular material of X-type heterocyclic perylene aromatic hydrocarbon, as well as preparation and application thereof