Showing papers on "Intramolecular force published in 2023"

Effects of push-pull electronic substitutions on ESIPT reaction for BH-BA compound

Abstract: This work mainly focuses on exploring excited state hydrogen bond interactions and excited state intramolecular proton transfer (ESIPT) behaviors for the novel excitation wavelength dependent emission BH-BA fluorophore. Given substitutions of different push and pull electron groups could largely affect molecular properties, we also investigate BH-NH2 and BH-CF3 derivatives incidentally. Via probing into photo-induced hydrogen bonding effects, we infer O4-H5···N6 plays a more dominant role. Photo-related charge redistribution further reveal the ESIPT trend. Constructing potential energy surfaces (PESs), we elucidate the substituent-related ESIPT behavior only proceeds along with O4-H5···N6 hydrogen bonding wire rather than the O1-H2···N3 one.

Hydrogen Bond Donor and Unbalanced Ion Pair Promoter-Assisted Gold-Catalyzed Carbon–Oxygen Cross-Coupling of (Hetero)aryl Iodides with Alcohols

Abstract: We have developed an efficient gold-catalyzed C–O cross-coupling reaction of (hetero)aryl iodides with primary and secondary alcohols via an AuI–AuIII catalytic cycle. This protocol featured moisture/air insensitivity, simple operation, and excellent functional group tolerance. Good yields were obtained regardless of steric hindrance and electronic factor (electron-rich or poor) of substrates, and the chirality of chiral alcohol starting materials could be preserved. Our protocol worked well for both intermolecular and intramolecular couplings. In addition, the RuPhos ligand was applied to gold-catalyzed cross-couplings. An unbalanced ion pair promoter and hydrogen bond donor solvent might be crucial in this transformation.

ESIPT-Inspired Dual-Mode Photoswitches with Fast Molecular Isomerization in the Solid State.

Abstract: Photoswitchable materials with excellent optical performance have attracted considerable attention from researchers and have been applied in various fields. The development of excellent solid-state dual-mode photoswitches is an important but challenging task. Herein, we propose a new strategy to construct an excited-state intramolecular proton transfer-inspired photoswitches (DiAH-pht) that possesses aggregation-induced emission features and displays fast molecular isomerization process characterized by simultaneously solid-state absorption/fluorescence response. The mechanistic studies indicate that introduction of a bulky group can create a folded molecular conformation that provides adequate volume to facilitate the photoisomerization and the enhanced ESIPT effect can boost the isomerization process from the cis-keto to trans-keto forms in the solid state. The feasibility of our strategy was further demonstrated by the activated photoisomerization performance of the Schiff base derivatives. Furthermore, the high-contrast and fast recovery process make DiAH-pht a highly promising candidate in the fields of dual-mode information encryption and high-density data storage.

Conjugation-Modulated Excitonic Coupling Brightens Multiple Triplet Excited States

Abstract: The design and regulation of multiple room-temperature phosphorescence (RTP) processes are formidably challenging due to the restrictions imposed by Kasha’s rule. Here, we report a general design principle for materials that show multiple RTP processes, which is informed by our study of four compounds where there is modulation of the linker hybridization between donor (D) and acceptor (A) groups. Theoretical modeling and photophysical experiments demonstrate that multiple RTP processes can be achieved in sp3 C-linked D–A compounds due to the arrest of intramolecular electronic communication between two triplet states (T1H and T1L) localized on the donor and acceptor or between two triplet states, one localized on the donor and one delocalized across aggregated acceptors. However, for the sp2 C-linked D–A counterparts, RTP from one locally excited T1 state is observed because of enhanced excitonic coupling between the two triplet states of molecular subunits. Single-crystal and reduced density gradient analyses reveal the influence of molecular packing on the coincident phosphorescence processes and the origin of the observed aggregate phosphorescence. These findings provide insights into higher-lying triplet excited-state dynamics and into a fundamental design principle for designing compounds that show multiple RTP.

Enantioselective Total Synthesis of (−)-Himalensine A via a Palladium and 4-Hydroxyproline Co-catalyzed Desymmetrization of Vinyl-bromide-tethered Cyclohexanones

Abstract: Herein, we describe the convergent enantioselective total synthesis of himalensine A in 18 steps, enabled by a highly enantio- and diastereoselective construction of the morphan core via a palladium/hydroxy proline co-catalyzed desymmetrization of vinyl-bromide-tethered cyclohexanones. The reaction pathway was illuminated by density functional theory calculations, which support an intramolecular Heck reaction of an in situ-generated enamine intermediate, where exquisite enantioselectivity arises from intramolecular carboxylate coordination to the vinyl palladium species in the rate- and enantio-determining carbopalladation steps. The reaction tolerates diverse N-derivatives, all-carbon quaternary centers, and trisubstituted olefins, providing access to molecular scaffolds found in a range of complex natural products. Following large-scale preparation of a key substrate and installation of a β-substituted enone moiety, the rapid construction of himalensine A was achieved using a highly convergent strategy based on an amide coupling/Michael addition/allylation/ring-closing metathesis sequence which allowed the introduction of three of the five rings in only three synthetic steps (after telescoping). Moreover, our strategy provides a new enantioselective access to a known tetracyclic late-stage intermediate that has been used previously in the synthesis of many Daphniphyllum alkaloids.

A double-cavity nor-seco-cucurbit[10]uril-based fluorescent probe for detection of ClO- and its application in cell imaging

Abstract: A supramolecular fluorescent probe based on double-cavity nor-seco-cucurbit[10]uril (ns-Q[10]) was constructed using the non-covalent host-guest interactions between ns-Q[10] and positively charged Astrazon Pink FG (APFG). The intramolecular charge transfer (ICT) effect induces the [email protected]ns-Q[10] probe to emit strong orange-red fluorescence. [email protected]ns-Q[10] exhibits desirable optical properties and low toxicity, and has been successfully applied to the imaging of HK2 and HeLa cells. When [email protected]ns-Q[10] interacts with ClO-, the CC double bond in APFG is oxidized and the molecule is cleaved, which leads to the fluorescence is quenched. The specificity and sensitivity of [email protected]ns-Q[10] to ClO- allows it to be used for the detection and tracking of ClO- in cells. [email protected]ns-Q[10] demonstrates good biocompatibility, which is an excellent foundation for its application in cell imaging.

Aggregation-induced emission active salicylaldehyde hydrazone with multipurpose sensing applications

Abstract: In this manuscript, the aggregation-induced emission (AIE) behaviour of a Schiff base salicylaldehyde hydrazone (SH) was investigated in DMSO-HEPES mixed solvents. The non-fluorescent SH in pure DMSO becomes a highly yellow-luminescent SH upon increasing the HEPES fraction ≥ 70 % in DMSO. The results of UV–vis, DLS, and SEM investigations supported the formation of SH self-aggregates, which inhibited the intramolecular rotation of SH and activated the excited state intramolecular proton transfer (ESIPT) mechanism to emit a bright yellow fluorescence at 535 nm. The AIEgen SH was applied for the sensing of cations, aldehydes, and nitroaromatics in HEPES buffer (5 % DMSO, 10 mM, pH 7.4) medium. The fluorescence of AIEgen SH was quenched by Cu2+, 2-hydroxy-5-nitrobenzaldehyde, and para-nitrophenol with a limit of detection of 3.74, 0.76, and 1.52 µM, respectively, among the other tested metal ions, aldehydes, and nitroaromatics. The cotton buds coated with the AIEgen SH were designed for the qualitative visual detection of Cu2+. The AIEgen SH was also employed for the detection of Cu2+ in mung bean sprouts. Moreover, the AIEgen SH was used to quantify the selective analytes in a real environmental water sample. Additionally, the AIEgen SH was employed to make yellow fluorescent gel and to visualize latent fingerprints (LFPs) on a non-porous glass slide.

Tuning Local Charge Distribution in Multicomponent Covalent Organic Frameworks for Dramatically Enhanced Photocatalytic Uranium Extraction.

Abstract: Optimizing the electronic structure of covalent organic framework (COF) photocatalysts is essential for maximizing photocatalytic activity. Herein, we report an isoreticular family of multivariate COFs containing chromenoquinoline rings in the COF structure and electron-donating or withdrawing groups in the pores. Intramolecular donor-acceptor (D-A) interactions in the COFs allowed tuning of local charge distributions and charge carrier separation under visible light irradiation, resulting in enhanced photocatalytic performance. By optimizing the optoelectronic properties of the COFs, a photocatalytic uranium extraction efficiency of 8.02 mg/g/day was achieved using a nitro-functionalized multicomponent COF in natural seawater, exceeding the performance of all COFs reported to date. Results demonstrate an effective design strategy towards high-activity COF photocatalysts with intramolecular D-A structures not easily accessible using traditional synthetic approaches.

Photoinduced Hydration Boosts O2 Evolution on Co-Chelating Covalent Organic Framework

Abstract: The achievement of artificial photosynthesis relies on successful water oxidation and a detailed mechanistic understanding. Here, we demonstrate a photoinduced hydration pathway for O2 evolution from water oxidation over an imine-linked covalent organic framework (COF) comprising electron-rich benzotrithiophene and electron-deficient benzothiadiazole units with atomically chelated Co sites. The experimental and theoretical results suggest that the water oxidation starts with the photoinduced hydration of imine groups. The subsequent oxidative deprotonation and intramolecular hydroxyl attack lead to O–O bond formation. The hydration path significantly averages the energy barriers of water oxidation, thus promoting O2 evolution. Inspired by this fact, we fabricate a COF-based heterostructure, which realizes overall water splitting with H2 and O2 evolution rates of 450 and 212 μmol·g–1 h–1, respectively.

Visible-Light Promoted Intramolecular para-Cycloadditions on Simple Aromatics.

Abstract: Dearomative cycloadditions are a powerful tool to access a large chemical space exploiting simple and ubiquitous building blocks. The energetic burden due to the loss of aromaticity has however greatly limited their synthetic potential. We devised a general intramolecular method that overcomes these limitations thanks to the photosensitation of allenamides. The visible-light-promoted process gives complex [2.2.2]-(hetero)-bicyclooctadienes at room temperature, likely through the stabilization of transient (bi)radicals by naphthalene. The reaction tolerates several valuable functionalities, offering a convenient handle for a myriad of applications, including original isoindoles and metal complexes.

Metal‐Free Synthesis via Intramolecular Cyclization, Enzyme Inhibition Properties and Molecular Docking of Novel Isoindolinones

Abstract: Highly effective one-pot synthesis of novel isoindolinones from various 2-benzoylbenzoic acid derivatives with intramolecular cyclization in the presence of chlorosulfonyl isocyanate was reported in mild conditions in the absence a metal catalyst. Novel synthesized compounds were tested against some metabolic enzymes including acetylcholinesterase (AChE), butyrylcholinesterase (BChE), α-glycosidase and carbonic anhydrase I and II (hCA I and hCA II) enzymes that associated with Alzheimer's disease (AD), type-2 diabetes mellitus (T2DM), epilepsy, and glaucoma. A series of novel isoindolinones (2 a–l) were evaluated as highly potent inhibition ability toward AChE (Kis: 2.33–13.81 μM), BChE (Kis: 1.45–12.27 μM), α-glycosidase (Kis: 8.03–23.05 μM), hCA I (Kis: 2.23–17.35 μM) and hCA II (Kis: 2.86–18.13 μM). Also, for these inhibitors, in silico molecular docking simulations and calculations were done with the Autodock Vina program to support the in vitro experimental studies.

Chelating Bis-silylenes As Powerful Ligands To Enable Unusual Low-Valent Main-Group Element Functions.

Abstract: ConspectusSilylenes are divalent silicon species with an unoccupied 3p orbital and one lone pair of electrons at the SiII center. Owing to the excellent σ-donating ability of amidinato-based silylenes, which stems from the intramolecular imino-N donor interaction with the vacant 3p orbital of the silicon atom, N-heterocyclic amidinato bis(silylenes) [bis(NHSi)s] can serve as versatile strong donating ligands for cooperative stabilization of central atoms in unusually low oxidation states. Herein, we present our recent achievement on the application of bis(NHSi) ligands with electronically and spatially different spacers to main-group chemistry, which has allowed the isolation of a variety of low-valent compounds consisting of monatomic zero-valent group 14 E0 complexes (named "metallylones", E = Si, Ge, Sn, Pb); monovalent group 15 EI complexes (E = N, P, isoelectronic with metallylones); and diatomic low-valent E2 complexes (E = Si, Ge, P) with intriguing electronic structures and chemical reactivities.The role of the SiII···SiII distance was revealed to be crucial in this chemistry. Utilizing the pyridine-based bis(NHSi) (Si···Si distance: 7.8 Å) ligand, germanium(0) complexes with additional Fe(CO)4 protection at the Ge0 site have been isolated. Featuring a shorter Si···Si distance of 4.3 Å, the xanthene-based bis(NHSi) has allowed the realization of the full series of heavy zero-valent group 14 element E0 complexes (E = Si, Ge, Sn, Pb), while the o-carborane-based bis(NHSi) (Si···Si distance: 3.3 Å) has enabled the isolation of Si0 and Ge0 complexes. Remarkably, reduction of the o-carborane-based bis(NHSi)-supported Si0 and Ge0 complexes induces the movement of two electrons into the o-carborane core and provides access to SiI-SiI and GeI-GeI species as oxidation products. Additionally, the o-carborane-based bis(NHSi) reacts with adamantyl azide, leading to a series of nitrogen(I) complexes as isoelectronic species of a carbone (C0 complex). Moreover, cooperative activation of white phosphorus gives bis(NHSi)-supported phosphorus complexes with varying and unexpected electronic structures when employing the xanthene-, o-carborane-, and aniline-based bis(NHSi)s. With the better kinetic protection provided by the xanthene-based bis(NHSi), small-molecule activation and functionalization of the bis(NHSi)-supported central E or E2 atoms (E = Si, Ge, P) are possible and furnish several novel functionalized silicon, germanium, and phosphorus compounds.With knowledge of the ability of chelating bis(NHSi)s in coordinating and functionalizing low-valent group 14 and 15 elements, the application of these ligand systems to other main-group elements such as group 2 and 13 is quite promising. To fully understand the role of the NHSi in a bis(NHSi) ligand, introducing a mixed ligand, i.e., the combination of an NHSi with other functional groups, such as Lewis acidic borane or Lewis basic borylene, in one chelating ligand could lead to new types of low-valent main-group species. Furthermore, the development of a genuine acyclic silylene, without an imino-N interaction with the vacant 3p orbital at the silicon(II) atom, as part of a chelating bis(acyclic silylene) has the potential to form very electronically different main-group element complexes that could achieve even more challenging bond activations such as N2 or unactivated C-H bonds.

Phosphaphenanthrene-Functionalized Benzoxazines Bearing Intramolecularly Hydrogen-Bonded Phenolic Hydroxyl: Synthesis, Structural Characterization, Polymerization Mechanism, and Property Investigation

Abstract: Hydrogen bonding in thermosetting resins can have a significant influence on the polymerization processes and the properties of corresponding thermosets, but its role in the polymerization of benzoxazine resins remains unclear. Here, we synthesized two novel phosphaphenanthrene-functionalized benzoxazine monomers from 2-6-oxido-6H-dibenz-[c,e][1,2]oxaphosphorin-1,4-dihydroxy phenylene, aniline/furfurylamine, and paraformaldehyde and investigated the structures by 1H, 13C, and 31P NMR, Fourier transform infrared (FT-IR), elemental analysis, and high-resolution mass spectrometry. Ring-opening polymerizations of both monomers were then studied by differential scanning calorimetry (DSC) and in situ FT-IR spectroscopy, and the resulting thermosets exhibited high thermal stability and low flammability. Density functional theory (DFT) calculations suggested that intramolecular hydrogen bonds are preferably formed between the phenolic −OH and the P═O in the phosphaphenanthrene functionality for both monomers, which is in line with the experimental results. We proposed a cation-activated ring-opening polymerization mechanism where intramolecular hydrogen bonding plays a pivotal role. The combination of experimental and computational effort provides molecular-level insights into intramolecular hydrogen bonding and its role in polymerization mechanisms in benzoxazine chemistry as well as a new angle for the design of high-performance thermoset polymers.

Saddle-shaped aza-nanographene with multiple odd-membered rings

Abstract: A saddle-shaped aza-nanographene containing a central 1,4-dihydropyrrolo[3,2-b]pyrrole (DHPP) has been prepared via a rationally designed four-step synthetic pathway encompassing intramolecular direct arylation, the Scholl reaction, and finally photo-induced radical cyclization. The target non-alternant, nitrogen-embedded polycyclic aromatic hydrocarbon (PAH) incorporates two abutting pentagons between four adjacent heptagons forming unique 7−7−5−5−7−7 topology. Such a combination of odd-membered-ring defects entails a negative Gaussian curvature within its surface with a significant distortion from planarity (saddle height ≈ 4.3 Å). Its absorption and fluorescence maxima are located in the orange-red region, with weak emission originating from the intramolecular charge-transfer character of a low-energy absorption band. Cyclic voltammetry measurements revealed that this stable under ambient conditions aza-nanographene underwent three fully reversible oxidation steps (two one-electron followed by one two-electron) with an exceptionally low first oxidation potential of Eox1 = −0.38 V (vs. Fc/Fc+).

Ag–NHC Complexes in the π-Activation of Alkynes

Abstract: Silver–NHC (NHC = N-heterocyclic carbene) complexes play a special role in the field of transition-metal complexes due to (1) their prominent biological activity, and (2) their critical role as transfer reagents for the synthesis of metal-NHC complexes by transmetalation. However, the application of silver–NHCs in catalysis is underdeveloped, particularly when compared to their group 11 counterparts, gold–NHCs (Au–NHC) and copper–NHCs (Cu–NHC). In this Special Issue on Featured Reviews in Organometallic Chemistry, we present a comprehensive overview of the application of silver–NHC complexes in the p-activation of alkynes. The functionalization of alkynes is one of the most important processes in chemistry, and it is at the bedrock of organic synthesis. Recent studies show the significant promise of silver–NHC complexes as unique and highly selective catalysts in this class of reactions. The review covers p-activation reactions catalyzed by Ag–NHCs since 2005 (the first example of p-activation in catalysis by Ag–NHCs) through December 2022. The review focuses on the structure of NHC ligands and p-functionalization methods, covering the following broadly defined topics: (1) intramolecular cyclizations; (2) CO2 fixation; and (3) hydrofunctionalization reactions. By discussing the role of Ag–NHC complexes in the p-functionalization of alkynes, the reader is provided with an overview of this important area of research and the role of Ag–NHCs to promote reactions that are beyond other group 11 metal–NHC complexes.