[1]Benzothiophene-Fused Chiral Spiro Polycyclic Aromatic Compounds: Optical Resolution, Functionalization, and Optical Properties

Doubly Spiro-Conjugated Chiral Carbocycles Exhibiting SOMO-HOMO Inversion in Persistent Radical Cations

Persistent chiral organic open-shell systems have captured growing interest due to their potential applications in organic spintronic and optoelectronic devices. Nevertheless, the integration of configurationally stable chirality into an organic open-shell system continues to pose challenges in molecular design. The π-extended skeleton incorporated in spiro-conjugated carbocycles can provide robust chiroptical properties and a significant stabilization of the excited and ionic radical states. However, this approach has been relatively less explored in the design of persistent organic open-shell systems. We report here the (S,S)-, (R,R)-, and meso-isomers of doubly spiro-conjugated carbocycles featuring flat and rigid carbon-bridged para-phenylenevinylene (CPV) of different conjugation lengths connected by two spiro-carbon centers, which we denote D-spiro-CPV for its quasi-dimeric structure. Our synthetic method based on a double lithiation cyclization approach enables facile production of D-spiro-CPV. D-spiro-CPVs exhibit circularly polarized luminescence (CPL) with high fluorescence quantum yields (ΦFL) resulting in a high CPL brightness of 21 M-1 cm-1 and also exhibit high thermal and photostability. The monoradical cation of D-spiro-CPV absorbing near-infrared light is notably persistent, exhibiting a half-life of 570 h under ambient conditions due to doubly spiro-conjugative stabilization. Theoretical and electrochemical studies indicate the radical cation of D-spiro-CPVs presents a non-Aufbau electron filling, exhibiting inversion of the energy level of the singly occupied molecular orbital (SOMO) and the highest (doubly) occupied molecular orbitals with the SOMO level even below the HOMO-1 level (double SHI effect). Our discoveries provide valuable insights into non-Aufbau molecules and the development of configurationally stable, optically active persistent radicals.

Recent Advances of Chiral Isolated and Small Organic Molecules: Structure and Properties for Circularly Polarized Luminescence

This paper explores recent advancements in the field of circularly polarized luminescence (CPL) exhibited by small and isolated organic molecules. The development and application of small CPL molecule are systematically reviewed through eight different chiral skeleton sections. Investigating the intricate interplay between molecular structure and CPL properties, the paper aims at providing and enlighting novel strategies for CPL-based applications.

Optimal weak measurement scheme for chiral molecular detection based on photonic spin Hall effect

In this paper, we propose a precision method to measure the chiroptical signal of Artemisinin solutions using the photonic spin Hall effect (PSHE) on the Ce:YIG-YIG-SiO2 structure as a probe. The effects of transmission distance, incident angles, applied magnetic fields of different directions, and beam waist of light on the weak measurement system are analytically investigated through simulations. It is found that decreasing the beam waist of the incident spot, increasing the incident angle, increasing the transmission distance, and adding a longitudinal magnetic field is conducive to enhancing the amplification transverse shift of PSHE, thus the measurement sensitivity is greatly improved. Based on the optimal weak measurement scheme, the detection limit for concentration measurement of artemisinin based on optical rotatory (OR) was reduced to 0.05 mg/ml. The measurement precision of the OR angle has been improved to 10-7rad.

Preparation, Aromaticity, and Bromination of Spiro Iridafurans

Iridium centers of [Ir(μ-Cl)(C8H14)2]2 (1) activate the Cβ(sp2)-H bond of benzylideneacetone to give [Ir(μ-Cl){κ2-C,O-[C(Ph)CHC(Me)O]}2]2 (2), which is the starting point for the preparation of the spiro iridafurans IrCl{κ2-C,O-[C(Ph)CHC(Me)O]}2(PiPr3) (3), [Ir{κ2-C,O-[C(Ph)CHC(Me)O]}2(MeCN)2]BF4 (4), [Ir(μ-OH){κ2-C,O-[C(Ph)CHC(Me)O]}2]2 (5), Ir{κ2-C,O-[C(Ph)CHC(Me)O]}2{κ2-C,N-[C6MeH3-py]} (6), and Ir{κ2-C,O-[C(Ph)CHC(Me)O]}2{κ2-O,O-[acac]} (7). The five-membered rings are orthogonally arranged with the oxygen atoms in trans in an octahedral environment of the iridium atom. Spiro iridafurans are aromatic. The degree of aromaticity and the negative charge of the CH-carbon of the rings depend on ligand trans to the carbon directly attached to the metal. Aromaticity has been experimentally confirmed by bromination of iridafurans with N-bromosuccinimide (NBS). Reactions are sensitive to the degree of aromaticity of the ring and the negative charge of the attacked CH-carbon. Iridafurans can be selectively brominated, when different ligands lie trans to metalated carbons. Bromination of 3 occurs in the ring with the metalated carbon trans to chloride, whereas the bromination of 6 takes place in the ring with the metalated carbon trans to pyridyl. The first gives IrCl{κ2-C,O-[C(Ph)CBrC(Me)O]}{κ2-C,O-[C(Ph)CHC(Me)O]}(PiPr3) (8), which reacts with more NBS to form IrCl{κ2-C,O-[C(Ph)CBrC(Me)O]}2(PiPr3) (9). The second yields Ir{κ2-C,O-[C(Ph)CBrC(Me)O]}{κ2-C,O-[C(Ph)CHC(Me)O]}{κ2-C,N-[C6MeH3-py]} (10). The origin of the selectivity is kinetic, with the rate-determining step of the reaction being the NBS attack. The activation energy depends on the negative charge of the attacked atom; a higher negative charge allows for a lower activation energy. Accordingly, complex 7 undergoes bromination in the acetylacetonate ligand, giving Ir{κ2-C,O-[C(Ph)CHC(Me)O]}2{κ2-O,O-[acacBr]} (11).

Furan-Containing Chiral Spiro-Fused Polycyclic Aromatic Compounds: Synthesis and Photophysical Properties

Spiro-fused polycyclic aromatic compounds (PACs) have received growing interest as rigid chiral scaffolds. However, furan-containing spiro-fused PACs have been quite limited. Here, we design spiro[indeno[1,2-b][1]benzofuran-10,10′-indeno[1,2-b][1]benzothiophene] as a new family of spiro-fused PACs that contains a furan unit. The compound was successfully synthesized in enantiopure form and also transformed to its S,S-dioxide derivative and the pyrrole-containing analog via aromatic metamorphosis. The absorption and emission properties of the obtained furan-containing chiral spiro-fused PACs are apparently different from those of their thiophene analogs that have been reported, owing to the increased electron-richness of furan compared to thiophene. All of the furan-containing chiral spiro-fused PACs were found to be circularly polarized luminescent materials.

Chiral Triarylborane-based Small Organic Molecules for Circularly Polarized Luminescence

Circularly polarized luminescence (CPL) has shown promising application potentials in 3D display, optical data storage, smart sensors/probers, CPL lasers, and light source for asymmetric photosynthesis. In the last decade, the CPL-active small organic molecules (CPL-SOMs) have attracted rapidly increasing research interest owing to the great advantages of SOMs, such as high luminescence efficiency, facile modification of chemical structure, fine emission wavelength tuning, precise relationships between structure and properties, and as well as easy fabrication. Promoted by the unique effects of boryl group, such as strong electron-accepting ability, great steric effect, and Lewis acidity to bind with Lewis bases, we herein summarized our recent research results about the creation of CPL-SOMs by modification of chiral scaffolds, such as [2.2]paracyclophane, [5]/[7]helicene, and binaphthyl, with boryl group. The preliminary results have well demonstrated that the chiral triarylborane-based SOMs exhibit promising CPL properties, such as intense CPL in combination of high luminescence dissymmetry factor (|g_lum |) with high fluorescence efficiency, solvent-induced sign inversion, facile emission wavelength tuning, high fluorescence efficiency in the solid, and substituent-induced sign inversion.

Electrical Detection of Molecular Transformations Associated with Chemical Reactions Using Graphene Devices

This study proposes a method to electrically detect chemical reactions that involve bond changes through reactions on graphene surfaces. To achieve a highly sensitive detection, we focused on the thiol-ene reaction that combines the maleimide and thiol groups. Graphene field-effect transistors (FETs) were used to detect the binding changes of the modified molecules. Graphene has high carrier mobility and is sensitive to changes in the electronic state of its surface. Graphene has been used as a sensor to detect low-concentration targets with high sensitivity. N-(9-Acridinyl)maleimide (NAM) was chosen as the modified molecule to immobilize maleimide on graphene through π-interaction, and methanethiol (MeSH) was set as the target thiol. The modification of NAM to graphene was first confirmed by attenuated total reflection Fourier transform infrared spectroscopy, and the modification density was 0.5 ± 0.1/nm² through cyclic voltammetry. Owing to a bond exchange, the transfer characteristics of the graphene FET shifted by 2 V to the negative direction after being exposed to MeSH at 10 parts per billion (ppb), equivalent to 0.2 ng, under ultraviolet irradiation. With 5000 ppb of acetic acid, it only shifted 0.7 V. With 1000 ppb of ethanol and 10,000 ppb of methanol, it shifted to the positive direction by 0.4 and 0.6 V, respectively. Because the nontarget molecule showed only a slight response, a thiol-ene chemical reaction was detected. The proposed method can detect the bond-change reaction using an ultralow concentration of MeSH, which indicates that at least 10 ppb (or 0.2 ng) of MeSH was detected by the graphene FET.

Chiral Benzo[b]silole-Fused 9,9'-Spirobi[fluorene]: Synthesis, Chiroptical Properties, and Transformation to π-Extended Polycyclic Arene

Chiral spiro π-conjugated compounds have emerged as a new class of circularly polarized luminescent organic materials. Here we report the synthesis and (chir)optical properties of a chiral benzo[b]silole-fused 9,9'-spirobi[fluorene] (SBF) and π-extended spiro polycyclic arene. The benzo[b]silole-fused SBF was successfully synthesized by a rhodium-catalyzed intramolecular silylative cyclization. It was further transformed to the chiral π-extended spiro polycyclic arene by an annulative π-extension reaction. Less effective spiroconjugation was observed for these spiro compounds through UV-Vis absorption spectroscopy and theoretical calculations. They exhibit circularly polarized luminescence with the dissymmetry factors of up to 0.76×10^-3 . Theoretical calculations demonstrate that emission of the benzo[b]silole-fused SBF occurs from one subunit, the structure of which is slightly different from that in the Frank-Condon state.

Construction of polysubstituted spiro[2.3] or [3.3] cyclic frameworks fused with a tosylated pyrrolidine promoted by visible-light-induced photosensitization

A novel visible-light-induced intramolecular [2 + 2] cycloaddition of methylenecyclopropanes (MCPs) for the rapid construction of polysubstituted spiro[2.3] or [3.3] cyclic frameworks fused with a tosylated pyrrolidine.

Three-Component Access to Functionalized Spiropyrrolidine Heterocyclic Scaffolds and Their Cholinesterase Inhibitory Activity

A novel one-pot [3+2]-cycloaddition reaction of (E)-3-arylidene-1-phenyl-succinimides, cyclic 1,2-diketones (isatin, 5-chloro-isatin and acenaphtenequinone), and diverse α-aminoacids such as 2-phenylglycine or sarcosine is reported. The reaction provides succinimide-substituted dispiropyrrolidine derivatives with high regio- and diastereoselectivities under mild reaction conditions. The stereochemistry of these N-heterocycles has been confirmed by four X-ray diffraction studies. Several synthetized compounds show higher inhibition on acetylcholinesterase (AChE) than butyrylcholinesterase (BChE). Of the 17 synthesized compounds tested, five exhibit good AChE inhibition with IC₅₀ of 11.42 to 22.21 µM. A molecular docking study has also been undertaken for compound 4n possessing the most potent AChE inhibitory activity, disclosing its binding to the peripheral anionic site of AChE enzymes.

Designing a near-infrared circularly polarized luminescent dye by dissymmetric spiro-fusion

A novel spiro-fused terrylene dimer (SDT) was designed and synthesized by a dissymmetric spiro-fusion strategy. The spiro-conjugation effect caused a distinct red-shift and enhancement of the absorption spectrum. Two chiral enantiomers of SDT have been absolutely resolved and identified in combination with theoretical calculations. Circularly polarized luminescence (CPL) measurement revealed its potential as a near-infrared chiral luminescent material.

Solvent-sensitive circularly polarized luminescent compounds bearing a 9,9′-spirobi[fluorene] skeleton

Chiral 9,9′-spirobi[fluorene] derivatives with a donor–π–acceptor system were prepared and found to exhibit solvent-sensitive circularly polarized luminescence.

Synthesis and chiroptical properties of stereogenic cyclic dimers based on 2,2′-biselenophene and [2.2]paracyclophane

2,2′-Biselenophenes embedded into a stereogenic cyclic structure exhibited remarkable chiroptical properties.

Spiro[pyrrol-benzopyran]-based probe with high asymmetry for chiroptical sensing via circular dichroism

We proposed an efficient approach to construct a novel spiro[pyrrol-benzopyran] scaffold with high asymmetry for reaction-based chiroptical sensing via circular dichroism.