The Nephelauxetic Effect Becomes an Important Design Factor for Photoactive First-Row Transition Metal Complexes

The expansion of d-orbitals as a result of metal-ligand bond covalence, the so-called nephelauxetic effect, is a well-established concept of coordination chemistry, yet its importance for the design of new photoactive complexes based on first-row transition metals is only beginning to be recognized. Until recently, much focus has been on optimizing the ligand field strength, coordination geometries, and molecular rigidity, but now it becomes evident that the nephelauxetic effect can be a game changer regarding the photophysical properties of 3d metal complexes in solution at room temperature. In Cr^III and Mn^IV complexes with the d³ valence electron configuration, the nephelauxetic effect was exploited to shift the well-known ruby-like red luminescence to the near-infrared spectral region. In Fe^II and Co^III complexes with the low-spin d⁶ electron configuration, charge-transfer excited states were stabilized with respect to detrimental metal-centered excited states, to improve their properties and to enhance their application potential. In isoelectronic (3d⁶) isocyanide complexes of Cr⁰ and Mn^I, the nephelauxetic effect is likely at play as well, enabling luminescence and other favorable photoreactivity. This minireview illustrates the broad applicability of the nephelauxetic effect in tailoring the photophysical and photochemical properties of new coordination compounds made from abundant first-row transition metals.     

Highly Cooperative CO2 Adsorption via a Cation Crowding Mechanism on a Cesium-Exchanged Phillipsite Zeolite

An understanding of the CO₂ adsorption mechanisms on small-pore zeolites is of practical importance in the development of more efficient adsorbents for the separation of CO₂ from N₂ or CH₄. Here we report that the CO₂ isotherms at 25–75 °C on cesium-exchanged phillipsite zeolite with a Si/Al ratio of 2.5 (Cs-PHI-2.5) are characterized by a rectilinear step shape: limited uptake at low CO₂ pressure (P_CO2) is followed by highly cooperative uptake at a critical pressure, above which adsorption rapidly approaches capacity (2.0 mmol g⁻¹). Structural analysis reveals that this isotherm behavior is attributed to the high concentration and large size of Cs⁺ ions in dehydrated Cs-PHI-2.5. This results in Cs⁺ cation crowding and subsequent dispersal at a critical loading of CO₂, which allows the PHI framework to relax to its wide pore form and enables its pores to fill with CO₂ over a very narrow range of P_CO2. Such a highly cooperative phenomenon has not been observed for other zeolites.     

Conjugated Nanohoop Polymers based on Antiaromatic Dibenzopentalenes for Charge Storage in Organic Batteries

With their bent π-systems, cyclic conjugation and inherent cavities, conjugated nanohoops are attractive for organic electronics applications. For ease of processing and morphological stability, an incorporation into polymers is desirable, but to date was hampered with few exceptions by synthetic difficulties. We herein present a unique strategy for the synthesis of conjugated nanohoop polymers using a dibenzo[a,e]pentalene (DBP) as central connector. We demonstrate this versatility by synthesizing three electronically diverse copolymers with dithienyldiketo(pyrrolopyrrol), fluorene and carbazole comonomers, and report the first donor-acceptor nanohoop polymer. Optoelectronic investigations reveal the prevalence of cyclic or linear conjugation, depending on the comonomer unit, and ambipolar electrochemical properties through the antiaromatic character of the DBP units. As the first report on using conjugated nanohoops for charge storage as positive electrode materials, we show a significant improvement in battery performance in a nanohoop-containing polymer compared to an equivalent nanohoop-free reference polymer. We believe this study will pave the way for the synthesis of a diverse range of nanohoop polymers and further stimulate their exploration for charge storage in batteries.     

N=8 Armchair Graphene Nanoribbons: Solution Synthesis and High Charge Carrier Mobility**

Structurally defined graphene nanoribbons (GNRs) have emerged as promising candidates for nanoelectronic devices. Low band gap (<1 eV) GNRs are particularly important when considering the Schottky barrier in device performance. Here, we demonstrate the first solution synthesis of 8-AGNRs through a carefully designed arylated polynaphthalene precursor. The efficiency of the oxidative cyclodehydrogenation of the tailor-made polymer precursor into 8-AGNRs was validated by FT-IR, Raman, and UV/Vis-near-infrared (NIR) absorption spectroscopy, and further supported by the synthesis of naphtho[1,2,3,4-ghi]perylene derivatives ( 1 and 2 ) as subunits of 8-AGNR , with a width of 0.86 nm as suggested by the X-ray single crystal analysis. Low-temperature scanning tunneling microscopy (STM) and solid-state NMR analyses provided further structural support for 8-AGNR . The resulting 8-AGNR exhibited a remarkable NIR absorption extending up to ∼2400 nm, corresponding to an optical band gap as low as ∼0.52 eV. Moreover, optical-pump TeraHertz-probe spectroscopy revealed charge-carrier mobility in the dc limit of ∼270 cm² V⁻¹ s⁻¹ for the 8-AGNR .     

Ruthenium-Catalyzed Direct Reductive Amination of Carbonyl Compounds for the Synthesis of Amines: An Overview

Reductive amination is a valuable method for amine synthesis that has been the topic of a century‘s worth of in-depth study in both academia and industry. Amines and their derivatives serve as incredibly adaptable building blocks for a broad array of organic substrates and are significant precursors for a myriad of advanced chemicals, physiologically active compounds, agrochemicals, biomolecules, pharmaceuticals, and polymers. The creation of innovative catalytic processes for the long-term and selective synthesis of amines from readily accessible and environmentally benign reagents remains a top priority in chemical research. Both heterogeneous and homogeneous catalysts have been designed with success to enable these reactions to explore new amines. Ruthenium catalysts are employed in reductive amination owing to their stability, selectivity, versatility, low toxicity, and high efficiency. This review comprehensively overviews the Ru-catalyzed reductive amination processes and includes the literature from 2009 to 2022.     

The Mechanical and Biological Performance of Photopolymerized Gelatin-Based Hydrogels as a Function of the Reaction Media

From the first experiments with biomaterials to mimic tissue properties, the mechanical and biochemical characterization has evolved extensively. Several properties can be described, however, what should be essential is to conduct a proper and physiologically relevant characterization. Herein, the influence of the reaction media (RM) and swelling media (SM)–phosphate buffered saline (PBS) and Dulbecco's modified Eagle's medium (DMEM) with two different glucose concentrations–is described in gelatin methacrylamide (GelMA) hydrogel mechanics and in the biological behavior of two tumoral cell lines (Caco-2 and HCT-116). All scaffolds are UV-photocrosslinked under identical conditions and evaluated for mass swelling ratio and stiffness. The results indicate that stiffness is highly susceptible to the RM, but not to the SM. Additionally, PBS-prepared hydrogels exhibited a higher photopolymerization degree according to high resolution magic-angle spinning (HR-MAS) NMR. These findings correlate with the biological response of Caco-2 and HCT-116 cells seeded on the substrates, which demonstrated flatter morphologies on stiffer hydrogels. Overall, cell viability and proliferation are excellent for both cell lines, and Caco-2 cells displayed a characteristic apical-basal polarization based on F-actin/Nuclei fluorescence images. These characterization experiments highlight the importance of conducting mechanical testing of biomaterials in the same medium as cell culture.     

On the Statistical Calibration of Physical Models

We introduce a novel statistical calibration framework for physical models, relying on probabilistic embedding of model discrepancy error within the model. For clarity of illustration, we take the measurement errors out of consideration, calibrating a chemical model of interest with respect to a more detailed model, considered as “truth” for the present purpose. We employ Bayesian statistical methods for such model‐to‐model calibration and demonstrate their capabilities on simple synthetic models, leading to a well‐defined parameter estimation problem that employs approximate Bayesian computation. The method is then demonstrated on two case studies for calibration of kinetic rate parameters for methane air chemistry, where ignition time information from a detailed elementary‐step kinetic model is used to estimate rate coefficients of a simple chemical mechanism. We show that the calibrated model predictions fit the data and that uncertainty in these predictions is consistent in a mean‐square sense with the discrepancy from the detailed model data.