Studies About the Effect of Halogenated Solvents on the Fluorescence Properties of 9-Aryl-Substituted Isoquinolinium Derivatives - A Case Study

It was demonstrated that 9-aryl-substituted isoquinolinium derivatives have significantly increased fluorescence quantum yields in halogenated solvents, mostly pronounced in chloroalkanes, which appears to be specific for this type of solvents. Further analysis with selected halogenated solvents revealed that the type and number of halogen substituents and the dielectric constant of the solvent have a distinct impact on the emission quantum yield. The solvent effect is explained by a solvation of the charge shift (CS) state by attractive halogen-π interactions (halogen bond), which impedes the torsional relaxation of the excited state.

Decoding the infrared spectra changes upon formation of molecular complexes: the case of halogen bonding in pyridine⋯perfluorohaloarene complexes

A recently developed computational scheme is employed to interpret changes in the infrared spectra of halogen-bonded systems in terms of intermolecular interaction energy components (electrostatic, exchange, induction, dispersion) taking pyridine⋯perfluorohaloarene complexes as examples. For all complexes, we find a strong linear correlation between the different terms of the interaction-induced changes of the IR band associated with an intermolecular halogen bond stretching mode and the corresponding terms of the interaction energy, which implies that the interaction components play similar roles in both properties. This is not true for other vibrational modes localized in one of the monomers studied here, for which the corresponding interaction-induced changes in IR bands may present a completely different decomposition than the interaction energy.

Design, synthesis, and herbicidal activity of novel phenoxypyridine derivatives containing natural product coumarin

BACKGROUND

In recent years, protoporphyrinogen oxidase (PPO, EC 1.3.3.4) inhibitors have been widely studied as important agricultural herbicides. Our research focused on the design and synthesis of novel PPO inhibitor herbicides, through linking of a diphenylether pyridine bioisostere structure to substituted coumarins, which aims to enhance environmental and crop safety while retaining high efficacy.

RESULTS

A total of 21 compounds were synthesized via acylation reactions and all compounds were characterized using infrared, ¹ H NMR, ¹³ C NMR, and high-resolution mass spectra. The respective configurations of compounds IV-6 and IV-12 were also confirmed using single crystal X-ray diffraction. The bioassay results showed that the title compounds displayed notable herbicidal activity, particularly compound IV-6 which displayed better herbicidal activity in greenhouse and field experiments, crop selectivity and safety for cotton and soybean compared with the commercial herbicide oxyfluorfen.

CONCLUSION

The work revealed that compound IV-6 deserves further attention as a candidate structure for a novel and safe herbicide. © 2021 Society of Chemical Industry.

Discovery of Novel Pyrazole-Quinazoline-2,4-dione Hybrids as 4-Hydroxyphenylpyruvate Dioxygenase Inhibitors

4-Hydroxyphenylpyruvate dioxygenase (HPPD, EC 1.13.11.27) has been identified as one of the most significant targets in herbicide discovery for resistant weed control. In a continuing effort to discover potent novel HPPD inhibitors, we adopted a ring-expansion strategy to design a series of novel pyrazole-quinazoline-2,4-dione hybrids based on the previously discovered pyrazole-isoindoline-1,3-dione scaffold. One compound, 3-(2-chlorophenyl)-6-(5-hydroxy-1,3-dimethyl-1H-pyrazole-4-carbonyl)-1,5-dimethylquinazoline-2,4(1H,3H)-dione (9bj), displayed excellent potency against AtHPPD, with an IC₅₀ value of 84 nM, which is approximately 16-fold more potent than pyrasulfotole (IC₅₀ = 1359 nM) and 2.7-fold more potent than mesotrione (IC₅₀ = 226 nM). Furthermore, the co-crystal structure of the AtHPPD-9bj complex (PDB ID 6LGT) was determined at a resolution of 1.75 Å. Similar to the existing HPPD inhibitors, compound 9bj formed a bidentate chelating interaction with the metal ion and a π-π stacking interaction with Phe381 and Phe424. In contrast, o-chlorophenyl at the N3 position of quinazoline-2,4-dione with a double conformation was surrounded by hydrophobic residues (Met335, Leu368, Leu427, Phe424, Phe392, and Phe381). Remarkably, the greenhouse assay indicated that most compounds displayed excellent herbicidal activity (complete inhibition) against at least one of the tested weeds at the application rate of 150 g of active ingredient (ai)/ha. Most promisingly, compounds 9aj and 9bi not only exhibited prominent weed control effects with a broad spectrum but also showed very good crop safety to cotton, peanuts, and corn at the dose of 150 g of ai/ha.

Halogen-Bond Assisted Photoinduced Electron Transfer

The formation of a halogen-bond (XB) complex in the excited state was recently reported with a quadrupolar acceptor–donor–acceptor dye in two iodine-based liquids (J. Phys. Chem. Lett.2017, 8, 3927–3932). The ultrafast decay of this excited complex to the ground state was ascribed to an electron transfer quenching by the XB donors. We examined the mechanism of this process by investigating the quenching dynamics of the dye in the S₁ state using the same two iodo-compounds diluted in inert solvents. The results were compared with those obtained with a non-halogenated electron acceptor, fumaronitrile. Whereas quenching by fumaronitrile was found to be diffusion controlled, that by the two XB compounds is slower, despite a larger driving force for electron transfer. A Smoluchowski–Collins–Kimball analysis of the excited-state population decays reveals that both the intrinsic quenching rate constant and the quenching radius are significantly smaller with the XB compounds. These results point to much stronger orientational constraint for quenching with the XB compounds, indicating that electron transfer occurs upon formation of the halogen bond.

Impact of Hydrogen Bonding on the Fluorescence of N-Amidinated Fluoroquinolones

The fluorescence properties of AIE-active N-amidinated fluoroquinolones, efficiently obtained by a perfluoroaryl azide-aldehyde-amine reaction, have been studied. The fluorophores were discovered to elicit a highly sensitive fluorescence quenching response towards guest molecules with hydrogen-bond-donating ability. This effect was evaluated in a range of protic/aprotic solvents with different H-bonding capabilities, and also in aqueous media. The influence of acid/base was furthermore addressed. The hydrogen-bonding interactions were studied by IR, NMR, UV/Vis and time-resolved fluorescence decay, revealing their roles in quenching of the fluorescence emission. Due to the pronounced quenching property of water, the N-amidinated fluoroquinolones could be utilized as fluorescent probes for quantifying trace amount of water in organic solvents.

Halogen-Bond-Assisted Photoluminescence Modulation in Carbazole-Based Emitter

Halogen bonding between a carbazole-based, pyridine-substituted organic semiconductor and a common halogen-bond donor (pentafluoroiodobenzene) yields efficient halogen-bond-driven fluorescence modulation in solution. Steady-state, time-resolved emission and absorption spectroscopy as well as density functional theory studies demonstrate that the fluorescence modulation arises from halogen-bond-induced intramolecular charge transfer. Fluorescence modulation offers a range of possibilities both in solution and in the solid state, for instance providing a potential pathway for the design of tunable luminescent materials for light-emitting devices.

Halogen bond triggered aggregation induced emission in an iodinated cyanine dye for ultra sensitive detection of Ag nanoparticles in tap water and agricultural wastewater

Aggregation induced emission (AIE) has emerged as a powerful method for sensing applications. Based on AIE triggered by halogen bond (XB) formation, an ultrasensitive and selective sensor for picomolar detection of Ag nanoparticles (Ag NPs) is reported. The dye (CyI) has an iodine atom in its skeleton which functions as a halogen bond acceptor, and aggregates on the Ag NP plasmonic surfaces as a halogen bond donor or forms halogen bonds with the vacant π orbitals of silver ions (Ag⁺). Formation of XB leads to fluorescence enhancement, which forms the basis of the Ag NPs or Ag⁺ sensor. The sensor response is linearly dependent on the Ag NP concentration over the range 1.0–8.2 pM with an LOD of 6.21 pM (σ = 3), while for Ag⁺ it was linear over the 1.0–10 μM range (LOD = 2.36 μM). The sensor shows a remarkable sensitivity for Ag NPs (pM), compared to that for Ag⁺ (μM). The sensor did not show any interference from different metal ions with 10-fold higher concentrations. This result indicates that the proposed sensor is inexpensive, simple, sensitive, and selective for the detection of Ag NPs in both tap and wastewater samples.

Based on AIE triggered by halogen bond (XB) formation, we established an ultrasensitive and selective sensor for picomolar detection of Ag nanoparticles (Ag NPs).

The Halogen Bond

The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.

Going beyond electrospray: mass spectrometric studies of chemical reactions in and on liquids

Recently developed and applied ionization techniques have brought mass spectrometry to bear on previously inaccessible chemistry. We offer our perspective on this field and its application for studying reaction mechanisms.

There has been a burst in the number and variety of available ionization techniques to use mass spectrometry to monitor chemical reactions in and on liquids. Chemists have gained the capability to access chemistry at unprecedented timescales, and monitor reactions and detect intermediates under almost any set of conditions. Herein, recently developed ionization techniques that facilitate mechanistic studies of chemical processes are reviewed. This is followed by a discussion of our perspective on the judicious application of these and similar techniques in order to study reaction mechanisms.

Structural investigation on toluene-3,4-dithiolatoantimony(iii) alkyldithiocarbonate complexes: thermal, powder XRD and biological studies

On thermal decomposition of the mixed sulfur donor antimony(iii) complexes, we obtained antimony sulfide at 600 °C, which was confirmed by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX).