Solution-phase synthesis of Clar's goblet and elucidation of its spin properties

In the traditional view, spin pairing occurs between two electrons in a chemical bond where the bonding interaction compensates for the penalty of electrostatic repulsion. It is a mystery whether spin pairing can occur between two non-bonded electrons within a molecular entity. Unveiling this type of spin entanglement (that is, pairing between two spatially segregated spins) at the molecular scale is a long-standing challenge. Clar's goblet, proposed by Erich Clar in 1972, provides an ideal platform to verify this unusual property. Here we report the solution-phase synthesis of Clar's goblet and experimental elucidation of its spin properties. Magnetic studies reveal that the two spins are spatially segregated with an average distance of 8.7 Å and antiferromagnetically coupled in the ground state with an ΔES-T of -0.29 kcal mol-1. Our results provide insight into the spin entanglement in Clar's goblet and may inspire the design of correlated molecular spins for quantum information technologies.

bay/ortho-Octa-substituted Perylene: A Versatile Building Block toward Novel Polycyclic (Hetero)Aromatic Hydrocarbons

ConspectusPolycyclic (hetero)aromatic hydrocarbons (PAHs) have emerged as a focal point in current interdisciplinary research, spanning the realms of chemistry, physics, and materials science. Possessing distinctive optical, electronic, and magnetic properties, these π-functional materials exhibit significant potential across diverse applications, including molecular electronic devices, organic spintronics, and biomedical functions, among others. Despite the extensive documentation of various PAHs over the decades, the efficient and precise synthesis of π-extended PAHs remains a formidable challenge, hindering their broader application. This challenge is primarily attributed to the intricate and often elusive nature of their synthesis, compounded by issues related to low solubility and unfavored stability.The development of π-building blocks that can be facilely and modularly transformed into diverse π-frameworks constitutes a potent strategy for the creation of novel PAH materials. For instance, based on the classic perylene diimide (PDI) unit, researchers such as Würthner, Wang, and Nuckolls have successfully synthesized a plethora of structurally diverse PAHs, as well as numerous other π-functional materials. However, until now the availability of such versatile building blocks is still severely limited, especially for those simultaneously having a facile preparation process, adequate solubilizing groups, favored material stability, and critically, rich possibilities for structural extension spaces.In this Account, we present an overview of our invention of a highly versatile bay-/ortho-octa-substituted perylene building block, designated as Per-4Br, for the construction of a series of novel PAH scaffolds with tailor-made structures and rich optoelectronic and magnetic properties. First, starting with a brief discussion of current challenges associated with the bottom-up synthesis of π-extended PAHs, we rationalize the key features of Per-4Br that enable facile access to new PAH molecules including its ease of large-scale preparation, favored material stability and solubility, and multiple flexible reaction sites, with a comparison to the PDI motif. Then, we showcase our rational design and sophisticated synthesis of a body of neutral or charged, closed- or open-shell, curved, or planar PAHs via controlled annulative π-extensions in different directions such as peripheral, diagonal, or multiple dimensions of the Per-4Br skeleton. In this part, the fundamental structure-property relationships between molecular conformations, electronic structures, and self-assembly behaviors of these PAHs and their unique physiochemical properties such as unusual open-shell ground states, global aromaticity, state-associated/stimuli-responsive magnetic activity, and charge transport characteristics will be emphatically elaborated. Finally, we offer our perspective on the continued advancement of π-functional materials based on Per-4Br, which, we posit, may stimulate heightened research interest in the versatile structural motifs typified by Per-4Br, consequently catalyzing further progress in the realm of organic π-functional materials.

Recent Advances in Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds

This review surveys recent progress in the chemistry of polycyclic heteroaromatic molecules with a focus on structural diversity and synthetic methodology. The article covers literature published during the period of 2016-2020, providing an update to our first review of this topic (Chem. Rev. 2017, 117 (4), 3479-3716).

Access to a Phthalazine Derivative Through an Angular cis-Quinacridone

Intramolecular electrophilic cyclization of a bisanthranilate afforded an angular cis-quinacridone compound, which condensed with hydrazine to give a phthalazine derivative. A [2+2+2] cyclization reaction occurred at the C-N double bond position of phthalazine when reacted with dimethyl acetylenedicarboxylate. The structures of these novel compounds were confirmed by crystallographic analysis. The phthalazine derivative decomposes back to quinacridone at ambient condition in the dark and as a solid with a half lifetime of about 22 months.

A diazabenzoperylene derivative as ratiometric fluorescent probe for cysteine with super large Stokes shift

Biothiols, including cysteine (Cys), homocysteine (Hcy), and glutathione (GSH), play key roles in biological processes, and detecting such thiols selectively is critical for understanding functions of biothiols. In this work, a pyridazine annelated perylene-based fluorescent probe PAPC is synthesized for highly selective detection of Cys. PAPC exhibits strong blue emission in PBS, while the red emission at 605 nm can be observed in the presence of Cys. The probe PAPC shows ratiometric fluorescence (I₆₀₅/I₄₆₀) detection of Cys with wide linear range of 1-120 μM and low detection limit of 0.19 μM. Super large Stokes shift (170 nm) and ratiometric fluorescence endow the probe low background signal. The discrimination of Cys over Hcy and GSH can be achieved through the difference of the ratiometric fluorescence. In addition, the probe has been proven to track Cys in real samples such as urine and HeLa cells. Therefore, PAPC probe is a promising candidate for detecting Cys in practical application. Graphical abstract.

Perylenequinone-based "turn on" fluorescent probe for hydrogen sulfide with high sensitivity in living cells

Hydrogen sulfide (H₂S) is a kind of gaseous signal molecule in many physiological processes. In order to detect H₂S, a novel "turn on" fluorescent probe 6,12-dihydroxyperylene-1,7-dione (DPD) was designed and synthesized. The probe DPD is fluorescence silence, while the addition of H₂S induces an obvious green fluorescence with an obvious color change from dark blue to yellow-green. The probe shows excellent selectivity, fast response (2.5min) and linear curve (0-90μM) in wide effective pH range (4-10). Competition experiments are also revealed in corresponding studies and the detection limit is 3.6μM. The response mechanism is proved to be the reduction of the probe by H₂S, which is confirmed by ¹H NMR. Furthermore, through the fluorescence turn-on signal toward H₂S in Hela cells, probe DPD was successfully applied to monitor H₂S in living Hela cells.

MoS2 Quantum Dot Growth Induced by S Vacancies in a ZnIn2S4 Monolayer: Atomic-Level Heterostructure for Photocatalytic Hydrogen Production

It is highly demanded to steer the charge flow in photocatalysts for efficient photocatalytic hydrogen reactions (PHRs). In this study, we developed a smart strategy to position MoS₂ quantum dots (QDs) at the S vacancies on a Zn facet in monolayered ZnIn₂S₄ (Vs-M-ZnIn₂S₄) to craft a two-dimensional (2D) atomic-level heterostructure (MoS₂QDs@Vs-M-ZnIn₂S₄). The electronic structure calculations indicated that the positive charge density of the Zn atom around the sulfur vacancy (Vs) was more intensive than other Zn atoms. The Vs confined in monolayered ZnIn₂S₄ established an important link between the electronic manipulation and activities of ZnIn₂S₄. The Vs acted as electron traps, prevented vertical transmission of electrons, and enriched electrons onto the Zn facet. The Vs-induced atomic-level heterostructure sewed up vacancy structures of Vs-M-ZnIn₂S₄, resulting in a highly efficient interface with low edge contact resistance. Photogenerated electrons could quickly migrate to MoS₂QDs through the intimate Zn-S bond interfaces. As a result, MoS₂QDs@Vs-M-ZnIn₂S₄ showed a high PHR activity of 6.884 mmol g^-1 h^-1, which was 11 times higher than 0.623 mmol g^-1 h^-1 for bulk ZnIn₂S₄, and the apparent quantum efficiency reached as high as 63.87% (420 nm). This work provides a prototype material for looking into the role of vacancies between electronic structures and activities in 2D photocatalytic materials and gives insights into PHR systems at the atomic level.

Bay- and Ortho-Octasubstituted Perylenes

A key intermediate compound, 2,5,8,11-tetrabromo-1,6,7,12-tetrabutoxyperylene (Per-4Br), was synthesized from 3,6-dibromo-2,7-dioxylnaphthalene via simple regioselective oxidative radical-radical coupling, followed by reduction and nucleophilic substitution. Various bay- and ortho-octasubstituted perylenes containing cyano, methoxy and aryl groups were then obtained by nucleophilic substitution or Pd-catalyzed coupling reactions. X-ray crystallographic analyses reveal that these new perylene molecules process a twisted structure due to steric congestion at the bay-regions and there is no obvious intermolecular π-π interaction. As a result, they exhibit moderate fluorescence quantum yields even in solid state. Therefore, Per-4Br can serve as a versatile building block for various functional perylene dyes with tunable optoelectronic property.