New members of fluorescent 1,8-naphthyridine-based BF2 compounds: selective binding of BF2 with terminal bidentate N^N^O and N^C^O groups and tunable spectroscopy properties

Two-Photon-Responsive "TICT + AIE" Active Naphthyridine-BF2 Photoremovable Protecting Group: Application for Specific Staining and Killing of Cancer Cells

The combined effects of twisted intramolecular charge transfer (TICT) and aggregation-induced emission (AIE) phenomena have demonstrated a significant influence on excited-state chemistry. These combined TICT and AIE features have been extensively utilized to enhance photodynamic and photothermal therapy. Herein, we demonstrated the synergistic capabilities of TICT and AIE phenomena in the design of the photoremovable protecting group (PRPG), namely, NMe2-Napy-BF2. This innovative PRPG incorporates TICT and AIE characteristics, resulting in four remarkable properties: (i) red-shifted absorption wavelength, (ii) strong near-infrared (NIR) emission, (iii) viscosity-sensitive emission property, and (iv) accelerated photorelease rate. Inspired by these intriguing attributes, we developed a nanodrug delivery system (nano-DDS) using our PRPG for cancer treatment. In vitro studies showed that our nano-DDS manifested effective cellular internalization, specific staining of cancer cells, high-resolution confocal imaging of cancerous cells in the NIR region, and controlled release of the anticancer drug chlorambucil upon exposure to light, leading to cancer cell eradication. Most notably, our nano-DDS exhibited a substantially increased two-photon (TP) absorption cross section (435 GM), exhibiting its potential for in vivo applications. This development holds promise for significant advancements in cancer treatment strategies.

Aggregation/Crystallization-Induced Emission in Naphthyridine-Based Carbazolyl-Modified Donor-Acceptor Boron Dyes Tunable by Fluorine Atoms

Four donor-acceptor boron difluoride complexes based on the carbazole electron donor and the [1,3,5,2]oxadiazaborinino[3,4-a][1,8]naphthyridine acceptor were designed, synthesized, and systematically spectroscopically investigated in solutions, in dye-doped polymer films, and in the solid states. The dyes exhibit an intense blue to red solid-state emission with photoluminescence quantum yields of up to 59 % in pure dye samples and 86 % in poly(methyl methacrylate) films. All boron complexes show aggregation-induced emission and reversible mechanofluorochromism. The optical properties of these dyes and their solid state luminescence can be tuned by substitution pattern, i. e., the substituents at the naphthyridine unit. Exchange of CH3- for CF3-groups does not only increase the intramolecular charge transfer character, but also provides a crystallization-induced emission enhancement.

Structure and bonding of proximity-enforced main-group dimers stabilized by a rigid naphthyridine diimine ligand

The development of ligands capable of effectively stabilizing highly reactive main-group species has led to the experimental realization of a variety of systems with fascinating properties. In this work, we computationally investigate the electronic, structural, energetic, and bonding features of proximity-enforced group 13-15 homodimers stabilized by a rigid expanded pincer ligand based on the 1,8-naphthyridine (napy) core. We show that the redox-active naphthyridine diimine (NDI) ligand enables a wide variety of structural motifs and element-element interaction modes, the latter ranging from isolated, element-centered lone pairs (e.g., E = Si, Ge) to cases where through-space π bonds (E = Pb), element-element multiple bonds (E = P, As) and biradical ground states (E = N) are observed. Our results hint at the feasibility of NDI-E₂ species as viable synthetic targets, highlighting the versatility and potential applications of napy-based ligands in main-group chemistry.

Recent Advances in BODIPY Compounds: Synthetic Methods, Optical and Nonlinear Optical Properties, and Their Medical Applications

Organoboron compounds are attracting immense research interest due to their wide range of applications. Particularly, low-coordinate organoboron complexes are receiving more attention due to their improbable optical and nonlinear optical properties, which makes them better candidates for medical applications. In this review, we summarize the various synthetic methods including multicomponent reactions, microwave-assisted and traditional pathways of organoboron complexes, and their optical and nonlinear properties. This review also includes the usage of organoboron complexes in various fields including biomedical applications.

Diphosphino-Functionalized 1,8-Naphthyridines: a Multifaceted Ligand Platform for Boranes and Diboranes

A 1,8-naphthyridine diphosphine (NDP) reacts with boron-containing Lewis acids to generate complexes featuring a number of different naphthyridine bonding modes. When exposed to diborane B2 Br4 , NDP underwent self-deprotonation to afford [NDP-B2 Br3 ]Br, an unsymmetrical diborane comprised of four fused rings. The reaction of two equivalents of monoborane BBr3 and NDP in a non-polar solvent provided the simple phosphine-borane adduct [NDP(BBr3 )2 ], which then underwent intramolecular halide abstraction to furnish the salt [NDP-BBr2 ][BBr4 ], featuring a different coordination mode from that of [NDP-B2 Br3 ]Br. Direct deprotonation of NDP by KHMDS or PhCH2 K generates mono- and dipotassium reagents, respectively. The monopotassium reagent reacts with one or half an equivalent of B2 (NMe2 )2 Cl2 to afford NDP-based diboranes with three or four amino substituents.

Synthesis of 1,8-Naphthyridines by the Ionic Liquid-Catalyzed Friedlander Reaction and Application in Corrosion Inhibition

A several of basic ionic liquids (ILs) were synthesized as green solvents and catalysts for the preparation of 1,8-naphthyridyl derivatives via the Friedlander reaction. [Bmmim][Im] exhibited remarkable catalytic activity to achieve the synthetic targets, and the reaction conditions were optimized. The model product 2,3-diphenyl-1,8-naphthyridine (1,8-Nap), with carboxyethylthiosuccinic acid (CETSA) to form an IL corrosion inhibitor ([1,8-Nap][CETSA]), and its corrosion inhibition performance for Q235 steel in 1 M HCl were researched by weight loss measurements, and the results showed that the inhibition efficiency was 96.95% when the concentration of [1,8-Nap][CETSA] was 1 mM at 35 °C. The electrochemical test verified that [1,8-Nap][CETSA] acted as a mixed-type inhibitor but mainly exhibited cathodic behavior. The inhibitor adsorbed on the metal surface was further proved by surface topography analysis.

Organolithium-Mediated Postfunctionalization of Thiazolo[3,2-c][1,3,5,2]oxadiazaborinine Fluorescent Dyes

An effective method for transition-metal-free postfunctionalization of thiazolo[3,2-c][1,3,5,2]oxadiazaborinine dyes via direct lithiation of the 1,3-thiazole ring was developed. The reaction allows valuable regioselective C-H modification of these N,O-chelated organoboron chromophores incorporating different groups, including C-, Hal-, Si-, S-, Se-, and Sn-substituents. As a result, a library of novel fluorescent 1,3-thiazole-based organoboron complexes has been synthesized and characterized. The influence of the donor/acceptor strength of the substituent E on the photophysical properties has been established. The compound with a bulky lipophilic substituent (SnBu₃) exhibits a relatively high solid-state photoluminescence quantum yield of 44%.

Fluorescent boron complexes based on new N,O-chelates as promising candidates for flow cytometry

This study presents the synthesis and optical properties of a new class of bright green-yellow fluorescent dyes with potential applications in bioimaging. A facile synthetic route via the chelation of aryl(hetaryl)aminoacryloylthiophene scaffolds with a BF2 fragment is presented. The photophysical properties of the dyes are attributed to the nature and position of electron-donating and electron-withdrawing substituents. Upon coordination to a BF2 fragment, characteristic emission was observed, with λem ranging from 503 to 543 nm and quantum yields of 0.14-0.42. Compared with parent aryl(hetaryl)aminoacryloylthiophenes, a significant red shift in absorption (up to 480 nm in solution) and emission (up to 543 nm in solution and 610 nm in the solid state) and high chemical stability and photostability were observed. The electron-accepting character of the substituents on the terminal aromatic ring or replacing this fragment with pyridine or pyrazine moieties resulted in increased quantum yields. To gain insight into the electronic structures and optical properties, quantum mechanical calculations were performed. The results of (TD-)DFT calculations supported the structural and spectroscopic data and showed the features of electronic distribution in the frontier molecular orbitals and active electrophilic and nucleophilic sites in the compounds investigated. Synthesized BF2 complexes are promising dyes for cell imaging and flow cytometry owing to their ready penetration and accumulation in cells.

Benzo[4,5]thiazolo[3,2- c][1,3,5,2]oxadiazaborinines: Synthesis, Structural, and Photophysical Properties

A family of highly emissive benzo[4,5]thiazolo[3,2- c][1,3,5,2]oxadiazaborinines, conjugated with the donor 4-dimethylaminophenyl group, was designed and synthesized. Their photophysical, both in solution and in the solid state, and structural properties were investigated. The influence of donor and acceptor substituents (R) in the benzothiazole unit on photophysical properties of complexes was found out. The tetrafluorobenzothiazole analogue exhibits nonbonded nuclear spin-spin coupling between fluorines from the BF₂ group and α-fluorine atom at the benzene ring. Additionally, this boron complex demonstrates a comparatively high solid-state fluorescence quantum yield (Φ = 0.34).

Fluorescent ZnII Chemosensor Mediated by a 1,8-Naphthyridine Derivative and It's Photophysical Properties

One of the greatest challenges in using fluorescent chemosensors for highly selective and sensitive transition-metal ions is finding an efficient and simple method for its synthesis. In this study, a highly efficient fluorescence chemosensor for ZnII was developed from N-Boc-L-proline modified 1,8-naphthyridine. The fluorescence intensity of the chemosensor was increased significantly only in the presence of ZnII ion which provided a perceived color change for rapid visual sensing, while other metal ions showed fluorescence quenching or little changes. It was worth noting that the chemosensor L distinguished ZnII from CdII commonly having similar properties. The solvent effect and possible bonding mode for fluorescence enhancement have been also discussed. Results of this study indicated that the Boc-group in l-proline significantly improved the sensitivity and selectivity for ZnII detection performance, as confirmed by comparison experiments and time dependent-density functional theory (TD-DFT) calculations.

N,O π-Conjugated 4-Substituted 1,3-Thiazole BF2 Complexes: Synthesis and Photophysical Properties

A series of 1,3-thiazole-based organoboron complexes has been designed and synthesized by acylation of 2-amino 4-subsituted 1,3-thiazoles with (4-dimethylamino)benzoyl chloride and the subsequent BF₂ complexation reaction. The influence of substituents in position 4 of the thiazole ring on photophysical properties of the complexes has been investigated. Synthesized thiazolo[3,2-c][1,3,5,2]oxadiazaborinines mainly showed intensive fluorescence in solutions. Complex with a 4,5-unsubstituted thiazole unit demonstrated an aggregation induced emission (AIE) effect and a very high fluorescent quantum yield (94%) in the solid state because of the inhibition of π-π/π-n interactions in the molecular packing.

Crystal structure of N-(7-di-bromo-methyl-5-methyl-1,8-naphthyridin-2-yl)benzamide-pyrrolidine-2,5-dione (1/1)

The title compound, C17H13Br2N3O·C4H5NO2, is a co-crystal of N-(7-di-bromo-methyl-5-methyl-1,8-naphthyridin-2-yl)benzamide and pyrrolidine-2,5-dione (succinimide). The benzamide mol-ecule exhibits pseudo-mirror symmetry, with an r.m.s. deviation of the non-H atoms of 0.09 Å (except for the two Br atoms). The angle between the least-squares planes of the two mol-ecules is 26.2 (2)°. In the crystal, the two mol-ecules are mutually linked by N-H⋯O and N-H⋯N hydrogen bonds. The packing is consolidated by C-H⋯(O,N) hydrogen bonds and π-π stacking inter-actions.

Crystal structure of 9-(dibromomethyl)-1,1-difluoro-3,7-dimethyl-1H-[1,3,5,2]oxadiazaborinino[3,4-a][1,8]naphthyridin-11-ium-1-uide

The mol­ecule in the title compound, C₁₂H₁₀BBr₂F₂N₃O, exhibits point group symmetry m.

The mol­ecule of the title 1,8-naphthyridine-BF₂ derivative, C₁₂H₁₀BBr₂F₂N₃O, is located on a mirror plane running parallel to the entire ring system and the attached methyl C atoms. Individual mol­ecules are stacked along the b-axis direction. The cohesion in the crystal structure is accomplished by C—H⋯F hydrogen bonds and additional off-set π–π inter­actions [centroid-to-centroid distance = 3.6392 (9) Å, slippage 0.472 Å], leading to the formation of a three-dimensional supra­molecular network.

1,1-Difluoro-3-phenyl-9-(pyridin-2-yl)-1H-1λ4,11λ4-1,3,5,2-oxadiazaborinino[3,4-a][1,8]naphthyridine

In the title compound, C20H13BF2N4O, the central fused three-ring oxadiazaborininonaphthyridine system is planar (r.m.s. deviation of 0.03 Å). The phenyl ring lies in the plane of this ring system, making a dihedral angle of 0.61 (14)°, and is inclined to the pyridine ring by 9.02 (19)°. In the crystal, molecules are connected by C—H...F hydrogen bonds, forming chains propagating along theb-axis direction. The chains are linked by offset π–π interactions [intercentroid distance = 3.4550 (13) Å], forming a three-dimensional supramolecular architecture.

The Influence of the π-Conjugated Spacer on Photophysical Properties of Difluoroboranyls Derived from Amides Carrying a Donor Group

A series of difluoroboranyls derived from amides carrying a variable π-conjugated spacer between the electron-donating (D) and electron-accepting (A) groups was synthesized and characterized with (1)H, (11)B, (13)C, (15)N, and (19)F NMR, electronic absorption, fluorescence spectroscopies, and first-principle calculations. The D-to-A distance in the series varied from 1.5 to 4.5 Å, causing bathochromic shifts of both the absorption and fluorescence maxima by more than 120 and 213 nm, respectively. These trends are rationalized by quantum-mechanical calculations that allow for quantification of the charge-transfer distance. Theoretical calculations were also performed to determine the vibronic couplings and thus to reproduce the experimental band shapes.