Computational study of the photophysical properties and electronic structure of iridium(III) photosensitizer complexes with electron-withdrawing groups.

A series of novel [Ir(tpy)(btp)Cl]+ complexes (Ir1-Ir4) have been reported to show excellent performance as photosensitizers. The introduction of electron-withdrawing groups increases visible light absorption and the lifetime of triplet states. To improve the photophysical properties, we theoretically design Ir5-Ir9 with electron-withdrawing groups (Cl, F, COOH, CN and NO2). Surprisingly, our findings indicate that the photosensitizer performance does not strictly increase with the electron-withdrawing ability of the substituents. In this work, the geometric and electronic structures, transition features, and photophysical properties of Ir1-Ir9 are investigated. The natural transition orbital (NTO) analysis indicates that the T1 and T2 states play a role in the photochemical pathways. Ultraviolet-visible (UV-vis) absorption spectra and charge-transfer spectra (CTS) have been investigated to show that the introduction of electron-withdrawing groups not only improves the visible light absorbing ability, but also changes the nature of electron excitation, providing a future molecular design strategy for similar series of photosensitizers. The rates of (reverse) intersystem crossing and the Huang-Rhys factors are evaluated to interpret the experimental results within the framework of Marcus theory. For complexes Ir1-Ir7, the introduction of electron-withdrawing groups leads to a lower efficiency of reverse intersystem crossing and a strong non-radiative process T2 → T1, resulting in a long triplet lifetime and excellent performance as a photosensitizer. Furthermore, some newly designed complexes (Ir7-Ir9) show great potential as thermally activated delayed fluorescence emitters, contrary to our initial expectations.

Exploring α-electron-deficiency-induced [1,2]-fluorine migration.

The present study investigates the standard model of [1,2]-fluorine migration and that triggered by the rearrangement of cyclopropyl-substituted fluoroepoxides. The [1,2]-fluorine migration reaction proceeds via a synchronous concerted, tight-ion-pair mechanism. When coupled with other reaction coordinates, the whole reaction follows an asynchronous mechanism, while the [1,2]-fluorince migration unit still retains its tight-ion-pair feature and the reaction coordinates of two C-F distances vary synchronously. A general reaction program for α-electron-deficiency-induced [1,2]-fluorine migration is proposed through an analysis of the intermediates generated from nucleophilic addition. The reaction mechanisms associated with α-electron deficiency and the rearrangement are scrutinized using computational chemistry. Two additional reaction programs for [1,2]-fluorine migration are identified. The Gibbs free energy change of [1,2]-fluorine migration exhibits a linear dependence on the value of the Fukui function of the substrate, which could lead to the production of the desired α-monofluoroketone and enhance the utilization of fluorine atoms.

Highly Efficient and Selective Visible-light Photocatalytic CO2 Reduction to CO Using a 2D Co(II)-Imidazole MOF as Cocatalyst and Ru(bpy)3 Cl2 as Photosensitizer.

The first application of an imidazole MOF, the 2D Co(II)- imidazole framework, {[Co(TIB)2 (H2 O)4 ]SO4 } (TIB stands for 1,3,5-tris(1-imidazolyl) benzene) (CoTIB) in photocatalytic CO2 reduction was carried out, and compared with that of ZIF-67. The CO2 /CoTIB (1.0 mg)/Ru(bpy)3 Cl2 (bpy=2,2'-bipyridine) (11.3 mg)/CH3 CN (40 mL)/TEOA (10 mL)/H2 O (400 µL) system produced 76.9 µmol of CO in 9 h, corresponding to the efficiency of 9.4 mmol g-1 h-1 (TOF: 7.3 h-1 ) with a >99% selectivity. Its catalytic activity is even higher than that of ZIF-67 based on TOF values. However, CoTIB is non-porous and has a very poor CO2 adsorption capacity and poor conductivity. Extensive photocatalytic experiments and energy-level diagrams suggest that the reduction did not depend on the CO2 adsorption by the cocatalyst, but can occur by the direct electron transfer from conduction-band maximum (CBM) of the cocatalyst to the zwitterionic alkylcarbonate adduct formed by the reaction of TEOA and CO2 . In addition, the process utilizes the short-lived singlet state (1 MLCT), not the long-lived triplet state (3 MLCT) of Ru(bpy)3 Cl2 to transfer electrons to the CBM of CoTIB. We found that the high efficiency of a cocatalyst, a photosensitizer, or a photocatalytic system depends on the matching of all related energy levels of the photosensitizer, the cocatalyst, CO2 , and the sacrificial agent in the reaction system.

Comment on "Realization of the Zn3+ oxidation state" by H. Fang, H. Banjade, Deepika and P. Jena, Nanoscale, 2021, 13, 14041-14048.

Two zinc-boron clusters (ZnBeB11(CN)12 and ZnBeB23(CN)22) reported in a theoretical study by P. Jena and co-workers are reinvestigated using quantum chemistry calculations. The results prove that the zinc atoms in these two clusters retain a normal oxidation state of +2, overturning the conclusion reached in the previous study that a +3 oxidation state is present. The semi-empirical LOBA method points out this contrast, which is demonstrated via various wavefunction analysis approaches. No unpaired electrons are observed on zinc atoms nor is there a spin density difference distribution, revealing that the zinc atoms have a fully occupied 3d10 electron shell. Density of states studies give the same conclusion, and they further show that zinc atoms adopt an sp2-hybrid type during bonding. From the perspective of energy, we advise that the electron affinity energy is not a reliable way of evaluating the oxidation state. Instead, binding energy calculations and constrained DFT are applicable, and these also support the presence of Zn2+. The simulated XPS peaks are consistent with the experimental data for Zn(II) measured in ZnS. Lastly, the ETS-NOCV method is adopted to give insights into the bonding structures between zinc atoms and boron clusters. It is suggested that future theoretical research into similar problems is analyzed more cautiously to avoid potentially misleading other researchers.

A Printed Paper-Based Anion Sensor Array for Multi-Analyte Classification: On-Site Quantification of Glyphosate.

We report a paper-based chemosensor array device (PCSAD) for the quantitative detection of oxyanions including the herbicide glyphosate (GlyP) in aqueous media. The mechanism of the oxyanion detection relies on a coordination-binding-based sensor array. In this study, the competitive coordination binding among Zn2+ , four catechol dyes, and seven oxyanions caused noticeable colour changes. The colour changes were employed for qualitative and quantitative analyses using an in-house automated image-processing algorithm with pattern recognition for digital images. A linear discrimination analysis discerned similarly structured oxyanions with 100 % accuracy. The regression analysis allowed the accurate quantification of GlyP in the herbicide products with a limit of detection of 16 mg/L, which is lower than the health advisory value for children (20 mg/L) stipulated by the environmental protection agency (EPA). PCSAD is a powerful sensor device for the on-site quantification of aqueous anions for environmental assessment.

96-Well Microtiter Plate Made of Paper: A Printed Chemosensor Array for Quantitative Detection of Saccharides.

Simple, rapid, and accurate detection methods for saccharides are potentially applicable to various fields such as clinical and food chemistry. However, the practical applications of on-site analytical methods are still limited. To this end, herein, we propose a 96-well microtiter plate made of paper as a paper-based chemosensor array device (PCSAD) for the simultaneous classification of 12 saccharides and the quantification of fructose and glucose among 12 saccharides. The mechanism of the saccharide detection relied on an indicator displacement assay (IDA) on the PCSAD using four types of catechol dyes, 3-nitrophenylboronic acid, and the saccharides. The design of the PCSAD and the experimental conditions for the IDA were optimized using a central composite design. The chemosensors exhibited clear color changes upon the addition of saccharides on the paper because of the competitive boronate esterification. The color changes were employed for the subsequent qualitative, semiquantitative, and quantitative analyses using an automated algorithm combined with pattern recognition for digital images. A qualitative linear discrimination analysis offered discrimination of 12 saccharides with a 100% classification rate. The semiquantitative analysis of fructose in the presence of glucose was carried out from the viewpoint of food analysis utilizing a support vector machine, resulting in clear discrimination of the various concentrations of fructose. Most importantly, the quantitative detection of fructose in two types of commercial soft drinks was also successfully carried out without sample pretreatments. Thus, the proposed PCSAD can be a powerful method for on-site food analyses that can meet the increasing demand from consumers for sensors of saccharides.

A Water-Gated Organic Thin-Film Transistor for Glyphosate Detection: A Comparative Study with Fluorescence Sensing.

Invited for the cover of this issue is the group of Tsuyoshi Minami at the University Tokyo. The image illustrates that despite being fabricated with the same polythiophene material, a water-gated organic thin-film transistor is a more sensitive device than a fluorescence sensor chip. Read the full text of the article at 10.1002/chem.202003529.

A Water-Gated Organic Thin-Film Transistor for Glyphosate Detection: A Comparative Study with Fluorescence Sensing.

This work reports the design of a highly sensitive solid-state sensor device based on a water-gated organic thin-film transistor (WG-OTFT) for the selective detection of herbicide glyphosate (GlyP) in water. A competitive assay among carboxylate-functionalized polythiophene, Cu2+ , and GlyP was employed as a sensing mechanism. Molecular recognition phenomena and electrical double layer (EDL) (at the polymer/water interface) originated from the field-effect worked cooperatively to amplify the sensitivity for GlyP. The limit of detection of WG-OTFT (0.26 ppm) was lower than that of a fluorescence sensor chip (0.95 ppm) which is the conventional sensing method. In contrast to the previously reported insulated molecular wires to block interchain interactions, molecular aggregates under the field-effect has shown to be effective for amplification of sensitivity through "intra"- and "inter"-molecular wire effects. The opposite strategy in this study could pave the way for fully utilizing the sensing properties of polymer-based solid-state sensor devices.

Supramolecular Sensor for Astringent Procyanidin C1: Fluorescent Artificial Tongue for Wine Components.

An artificial tongue that detects astringent components for a comprehensive evaluation of taste has not been established to date. Herein, we first propose fluorescent polythiophene (PT) derivatives (S1-S3) modified with 3-pyridinium boronic acid as supramolecular chemosensors for wine components including astringent procyanidin C1. After numerous attempts for the synthetic conditions, more than 95 mol % of the PT unit was modified with the pyridinium boronic acid moiety. To evaluate the PT derivatives as chemosensors of the artificial tongue, qualitative and quantitative analyses were performed with four types of wine components (i.e., sweet, sour, bitter, and astringent tastes) in combination with pattern recognition models. Notably, procyanidin C1 in the actual wine sample was successfully detected in a quantitative manner. In other words, we have established an authentic artificial tongue using PT based supramolecular chemosensors.

Fluorescence Anion Chemosensor Array Based on Pyrenylboronic Acid.

A novel fluorescence chemosensor array composed of pyrenylboronic acid-based probes for multi- anion detection has been developed. The pyrenylboronic acid derivatives showed fluorescence quenching or enhancement due to photoinduced electron transfer originating from anion binding. The recognition ability was assessed by fluorescence titrations and electrospray ionization mass spectrometry. Because the array is constructed with cross-reactive probes, the combination of differential binding affinities for anions (i.e., fluoride, acetate, oxalate, malonate, citrate, dihydrogen phosphate, and pyrophosphate) and pattern recognitions, such as linear discriminant analysis, offered a successful simultaneous anion detection with a classification rate of 100%. Furthermore, the chemosensor array allowed for quantitative prediction of oxalate, malonate, and citrate in mixtures using a support vector machine. Importantly, the array system employs low-cost and commercially available reagents as probes. Thus, this study could lead to the development of user-friendly and high-throughput methods to detect a variety of analytes in complicated systems.

Novel Polyimide Separator Prepared with Two Porogens for Safe Lithium-Ion Batteries.

A porous polyimide (PI) membrane is successfully prepared via nonsolvent-induced phase separation with two porogens: dibutyl phthalate and glycerin. The as-prepared uniform porous PI membrane shows excellent separator properties for lithium-ion batteries (LIBs). Compared with the commercial polyethylene (PE) separator, the PI separator exhibits significant thermal stability, better ionic conductivity, and wettability both in carbonate and ether electrolytes for LIBs. The battery coin-cells assembled with the PI separator is more robust and still works even after heating at 140 °C for 1 h, while the cells with the commercial PE separator could not charge any more due to the shrinkage of the PE under the same condition.

Simple Colorimetric Chemosensor Array for Oxyanions: Quantitative Assay for Herbicide Glyphosate.

Although the determination of oxyanions due to correlation with metabolic processes and diseases is in high demand, most of the developed methods are suffering from a shortage of a capability of on-site analysis, sensitivity, and user-friendliness. This paper introduces the first colorimetric chemosensor array targeting various anions including glyphosate. The proposed sensor benefits from some notable features such as utilizing only commercially available reagents, recognizing similarly structured compounds by biomaterial-free sensors, and providing a fingerprint-like response originating from pattern recognition. The detection mechanism is based on an anion sensing strategy named coordination binding-based sensor array (CBSA). In CBSA, competitive coordinative bonding of a metal ion (Zn2+) between a catechol dye (i.e., indicator) and target anions occurs, and changes in the optical properties of the dye represent the target's concentration. For data processing, two chemometrical techniques including linear discrimination analysis (LDA) and an artificial neural network (ANN) for pattern classification and regression/prediction purposes were successfully employed, respectively. Finally, the proposed chemosensor was subjected to glyphosate samples (commercial herbicide and tap water samples) and produced satisfactory results.

Corrigendum: A Saccharide Chemosensor Array Developed Based on an Indicator Displacement Assay Using a Combination of Commercially Available Reagents.

[This corrects the article DOI: 10.3389/fchem.2019.00049.].

A Saccharide Chemosensor Array Developed Based on an Indicator Displacement Assay Using a Combination of Commercially Available Reagents.

Herein, a very simple colorimetric chemosensor array is reported for saccharides (D-glucose, D-fructose, D-xylose, D-galactose, D-mannose, L-rhamnose, and N-acetyl-D-gluosamine). While various types of chemosensors for saccharides have been investigated extensively to-this-date, tremendous additional efforts are still required on a regular basis for the syntheses of new chemosensors. Complicated syntheses would be a bottleneck, given that artificial receptor-based chemosensing systems are not so popular in comparison to biomaterial-based (e.g., enzyme-based) sensing systems. Toward this end, chemosensor array systems using molecular self-assembled materials can avoid the abovementioned synthetic efforts and achieve simultaneous qualitative and quantitative detection of a number of guest saccharides. Using a practical approach, we focus on an indicator displacement assay (IDA) to fabricate a chemosensor array for colorimetric saccharide sensing. On this basis, 3-nitrophenylboronic acid (3-NPBA) spontaneously reacts with catechol dyes such as alizarin red S (ARS), bromopyrogallol red (BPR), pyrogallol red (PR), and pyrocatechol violet (PV), and yields boronate ester derivatives with color changes. The addition of saccharides into the aqueous solution of the boronate esters induces color recovery owing to the higher binding affinity of 3-NPBA for saccharides, thus resulting in the release of dyes. By employing this system, we have succeeded in discriminating saccharides qualitatively and quantitatively with a classification success rate of 100%. Most importantly, our chemosensor array has been fabricated by only mixing low cost commercially available reagents in situ, which means that complicated synthetic processes are avoided for saccharide sensing. We believe this simple colorimetric assay that uses only commercially available reagents can create new, user-friendly supramolecular sensing pathways for saccharides.