In Situ Synthesis of MnS Hollow Microspheres on Reduced Graphene Oxide Sheets as High-Capacity and Long-Life Anodes for Li- and Na-Ion Batteries

Uniform MnS hollow microspheres in situ crystallized on reduced graphene oxide (RGO) nanosheets via a facile hydrothermal method. The MnS/RGO composite material was used as the anode for Na-ion batteries for the first time and exhibited excellent cycling performance, superior specific capacity, and great cycle stability and rate capability for both Li- and Na-ion batteries. Compared with nonencapsulated pure MnS hollow microspheres, these MnS/RGO nanocomposites demonstrated excellent charge–discharge stability and long cycle life. Li-ion storage testing revealed that these MnS/RGO nanocomposites deliver high discharge–charge capacities of 640 mAh g^–1 at 1.0 A g^–1 after 400 cycles and 830 mAh g^–1 at 0.5 A g^–1 after 100 cycles. The MnS/RGO nanocomposites even retained a specific capacity of 308 mAh g^–1 at a current density of 0.1 A g^–1 after 125 cycles as the anode for Na-ion batteries. The outstanding electrochemical performance of the MnS/RGO composite attributed to the RGO nanosheets greatly improved the electronic conductivity and efficiently mitigated the stupendous volume expansion during the progress of charge and discharge

Long-Lived Room Temperature Deep-Red/Near-IR Emissive Intraligand Triplet Excited State (³IL) of Naphthalimide in Cyclometalated Platinum(II) Complexes and Its Application in Upconversion

[C^∧NPt­(acac)] (C^∧N = cyclometalating ligand; acac = acetylacetonato) complexes in which the naphthalimide (NI) moiety is directly cyclometalated (NI as the C donor of the C–Pt bond) were synthesized. With 4-pyrazolylnaphthalimide, isomers with five-membered (<b>Pt-2</b>) and six-membered (<b>Pt-3</b>) chelate rings were obtained. With 4-pyridinylnaphthalimide, only the complex with a five-membered chelate ring (<b>Pt-4</b>) was isolated. A model complex with 1-phenylpyrazole as the C^∧N ligand was prepared (<b>Pt-1</b>). Strong absorption of visible light (ε = 21 900 M^–1 cm^–1 at 443 nm for <b>Pt-3</b>) and room temperature (RT) phosphorescence at 630 nm (<b>Pt-2</b> and <b>Pt-3</b>) or 674 nm (<b>Pt-4</b>) were observed. Long-lived phosphorescences were observed for <b>Pt-2</b> (τ_P = 12.8 μs) and <b>Pt-3</b> (τ_P = 61.9 μs). <b>Pt-1</b> is nonphosphorescent at RT in solution because of the acac-localized T₁ excited state [based on density functional theory (DFT) calculations and spin density analysis], but a structured emission band centered at 415 nm was observed at 77 K. Time-resolved transient absorption spectra and spin density analysis indicated a NI-localized intraligand triplet excited state (³IL) for complexes <b>Pt-2</b>, <b>Pt-3</b>, and <b>Pt-4</b>. DFT calculations on the transient absorption spectra (T₁ → T_<i>n</i> transitions, <i>n</i> > 1) also support the ³IL assignment of the T₁ excited states of <b>Pt-2</b>, <b>Pt-3</b>, and <b>Pt-4</b>. The complexes were used as triplet sensitizers for triplet–triplet-annihilation (TTA) based upconversion, and the results show that <b>Pt-3</b> is an efficient sensitizer with an upconversion quantum yield of up to 14.1%, despite its low phosphorescence quantum yield of 5.2%. Thus, we propose that the sensitizer molecules at the triplet excited state that are otherwise nonphosphorescent were involved in the TTA upconversion process, indicating that weakly phosphorescent or nonphosphorescent transition-metal complexes can be used as triplet sensitizers for TTA upconversion

Facile Soaking Strategy Toward Simultaneously Enhanced Conductivity and Toughness of Self-Healing Composite Hydrogels Through Constructing Multiple Noncovalent Interactions

Tough and stretchable conductive hydrogels are desirable for the emerging field of wearable and implanted electronics. Unfortunately, most existing conductive hydrogels have low mechanical strength. Current strategies to enhance mechanical properties include employing tough host gel matrices or introducing specific interaction between conductive polymer and host gel matrices. However, these strategies often involve additional complicated processes. Here, a simple yet effective soaking treatment is employed to concurrently enhance mechanical and conductive properties, both of which can be facilely tailored by controlling the soaking duration. The significant improvements are correlated with co-occurring mechanism of deswelling and multiple noncovalent interactions. The resulting optimal sample exhibits attractive combination of high water content (75 wt %), high tensile stress (∼2.5 MPa), large elongation (>600%), reasonable conductivity (∼25 mS/cm), and fast self-healing property with the aid of hot water. The potential application of gel as a strain sensor is demonstrated. The applicability of this method is not limited to conductive hydrogels alone but can also be extended to strengthen other functional hydrogels with weak mechanical properties

Facile Soaking Strategy Toward Simultaneously Enhanced Conductivity and Toughness of Self-Healing Composite Hydrogels Through Constructing Multiple Noncovalent Interactions

Tough and stretchable conductive hydrogels are desirable for the emerging field of wearable and implanted electronics. Unfortunately, most existing conductive hydrogels have low mechanical strength. Current strategies to enhance mechanical properties include employing tough host gel matrices or introducing specific interaction between conductive polymer and host gel matrices. However, these strategies often involve additional complicated processes. Here, a simple yet effective soaking treatment is employed to concurrently enhance mechanical and conductive properties, both of which can be facilely tailored by controlling the soaking duration. The significant improvements are correlated with co-occurring mechanism of deswelling and multiple noncovalent interactions. The resulting optimal sample exhibits attractive combination of high water content (75 wt %), high tensile stress (∼2.5 MPa), large elongation (>600%), reasonable conductivity (∼25 mS/cm), and fast self-healing property with the aid of hot water. The potential application of gel as a strain sensor is demonstrated. The applicability of this method is not limited to conductive hydrogels alone but can also be extended to strengthen other functional hydrogels with weak mechanical properties

Molecular Structure–Intersystem Crossing Relationship of Heavy-Atom-Free BODIPY Triplet Photosensitizers

A thiophene-fused BODIPY chromophore displays a large triplet-state quantum yield (Φ_T = 63.7%). In contrast, when the two thienyl moieties are not fused into the BODIPY core, intersystem crossing (ISC) becomes inefficient and Φ_T remains low (Φ_T = 6.1%). First-principles calculations including spin–orbit coupling (SOC) were performed to quantify the ISC. We found larger SOC and smaller singlet–triplet energy gaps for the thiophene-fused BODIPY derivative. Our results are useful for studies of the photochemistry of organic chromophores

Different Quenching Effect of Intramolecular Rotation on the Singlet and Triplet Excited States of Bodipy

It is well-known that the fluorescence of a chromophore can be efficiently quenched by the free rotor effect, sometimes called intramolecular rotation (IMR), i.e. by a large-amplitude torsional motion. Using this effect, aggregation induced enhanced emission (AIE) and fluorescent molecular probes for viscosity measurements have been devised. However, the rotor effect on triplet excited states was rarely studied. Herein, with molecular rotors of Bodipy and diiodoBodipy, and by using steady state and time-resolved transient absorption/emission spectroscopies, we confirmed that the triplet excited state of the Bodipy chromophore is not quenched by IMR. This is in stark contrast to the fluorescence (singlet excited state), which is significantly quenched by IMR. This result is rather interesting since a long-lived excited state (triplet, 276 μs) is not quenched by the IMR, but the short-lived excited state (singlet, 3.8 ns) is quenched by the same IMR. The unquenched triplet excited state of the Bodipy was used for triplet–triplet annihilation upconversion, and the upconversion quantum yield is 6.3%