Search Results (442)

Using density functional theory (M06-2X-D3/def2-TZVP), we investigated the 1,2-addition reactions of NH₃ with a series of heavy imine analogues, G13=P-Rea (where G13 denotes a Group 13 element; Rea = reactant), featuring a mixed G13–P–Ga backbone. Theoretical analyses revealed that the bonding nature of the G13=P moiety in G13=P-Rea molecules varies with the identity of the Group 13 center. For G13=B, Al, Ga, and In, the bonding is best described as a donor–acceptor (singlet–singlet) interaction, whereas for G13=Tl, it is characterized by an electron-sharing (triplet–triplet) interaction. According to our theoretical studies, all G13=P-Rea species—except the Tl=P analogue—undergo 1,2-addition with NH₃ under favorable energetic conditions. Energy decomposition analysis combined with natural orbitals for chemical valence (EDA–NOCV), along with frontier molecular orbital (FMO) theory, reveals that the primary bonding interaction in these reactions originates from electron donation by the lone pair on the nitrogen atom of NH₃ into the vacant p-π* orbital on the G13 center. In contrast, a secondary, weaker interaction involves electron donation from the phosphorus lone pair of the G13=P-Rea species into the empty σ* orbital of the N–H bond in NH₃. The calculated activation barriers are primarily governed by the deformation energy of ammonia. Specifically, as the atomic weight of the G13 element increases, the atomic radius and G13–P bond length also increase, requiring a greater distortion of the H₂N–H bond to reach the transition state. This leads to a higher geometrical deformation energy of NH₃, thereby increasing the activation barrier for the 1,2-addition reaction involving these Lewis base-stabilized, heavy imine-like G13=P-Rea molecules and ammonia. Full article

Video temporal grounding (VTG) aims to localize a semantically relevant temporal segment within an untrimmed video based on a natural language query. The task continues to face challenges arising from cross-modal semantic misalignment, which is largely attributed to redundant visual content in sensor-acquired video streams, linguistic ambiguity, and discrepancies in modality-specific representations. Most existing approaches rely on intra-modal feature modeling, processing video and text independently throughout the representation learning stage. However, this isolation undermines semantic alignment by neglecting the potential of cross-modal interactions. In practice, a natural language query typically corresponds to spatiotemporal content in video signals collected through camera-based sensing systems, encompassing a particular sequence of frames and its associated salient subregions. We propose a text-guided visual representation optimization framework tailored to enhance semantic interpretation over video signals captured by visual sensors. This framework leverages textual information to focus on spatiotemporal video content, thereby narrowing the cross-modal gap. Built upon the unified cross-modal embedding space provided by CLIP, our model leverages video data from sensing devices to structure representations and introduces two dedicated modules to semantically refine visual representations across spatial and temporal dimensions. First, we design a Spatial Visual Representation Optimization (SVRO) module to learn spatial information within intra-frames. It selects salient patches related to the text, capturing more fine-grained visual details. Second, we introduce a Temporal Visual Representation Optimization (TVRO) module to learn temporal relations from inter-frames. Temporal triplet loss is employed in TVRO to enhance attention on text-relevant frames and capture clip semantics. Additionally, a self-supervised contrastive loss is introduced at the clip–text level to improve inter-clip discrimination by maximizing semantic variance during training. Experiments on Charades-STA, ActivityNet Captions, and TACoS, widely used benchmark datasets, demonstrate that our method outperforms state-of-the-art methods across multiple metrics. Full article

This study investigates the nonlinear aeroelastic behavior and energy harvesting performance of a two-degrees-of-freedom NACA 0012 airfoil under varying reduced velocities and electrical load resistances. The system exhibits a range of dynamic responses, including periodic and chaotic states, governed by strong fluid–structure interactions. Nonlinear oscillations first appear near the critical reduced velocity $U_r^{*}=6$, with large-amplitude limit-cycle oscillations emerging around $U_r^{*}=8$ in the absence of the electrical loading. As the load resistance increases, this transition shifts to higher $U_r^{*}$, reflecting the damping effect of the electrical load. Fourier spectra reveal the presence of odd and even superharmonics in the lift coefficient, indicating nonlinearities induced by fluid–structure coupling, which diminishes at higher resistances. Phase portraits and Poincaré maps capture transitions across dynamical regimes, from periodic to chaotic behavior, particularly at a low resistance. The voltage output correlates with variations in the lift force, reaching its maximum at an intermediate resistance before declining due to a suppressing nonlinearity. Flow visualizations identify various vortex shedding patterns, including single (S), paired (P), triplet (T), multiple-pair (mP) and pair with single (P + S) that weaken at higher resistances and reduced velocities. The results demonstrate that nonlinearity plays a critical role in efficient voltage generation but remains effective only within specific parameter ranges. Full article

Achieving high quantum yields for Yb³⁺ ion emission in complexes with organic ligands is a challenging task, as most Yb³⁺ complexes with such ligands typically exhibit efficiencies below 3.5%. Our research demonstrates that the introduction of heavy atom-containing ancillary ligands, such as TPPO or TPAO, along with the careful engineering of the main β-diketone ligand, can increase the luminescence efficiency up to 20-fold by the alteration of the energy migration pathway. It is demonstrated that the combination of two distinct organic ligands leads to the blockage of singlet–triplet intersystem crossing (ISC), alongside electronic energy transfer from β-diketone to Yb³⁺ ions through charge transfer states. The synthesized complexes exhibit quantum yields of 6.5% and 7.0% in the solid state, which places them at the top globally among this class of materials with simple non-deuterated and non-fluorinated ligands. Full article

Precise identification and quantification of fish movement states are of significant importance for conducting fish behavior research and guiding aquaculture production, with object tracking serving as a key technical approach for achieving behavioral quantification. The traditional DeepSORT algorithm has been widely applied to object tracking tasks; however, in practical aquaculture environments, high-density cultured fish exhibit visual characteristics such as similar textural features and frequent occlusions, leading to high misidentification rates and frequent ID switching during the tracking process. This study proposes an underwater fish object tracking method based on the improved DeepSORT algorithm, utilizing ResNet as the backbone network, embedding Deformable Convolutional Networks v2 to enhance adaptive receptive field capabilities, introducing Triplet Loss function to improve discrimination ability among similar fish, and integrating Convolutional Block Attention Module to enhance key feature learning. Finally, by combining the aforementioned improvement modules, the ReID feature extraction network was redesigned and optimized. Experimental results demonstrate that the improved algorithm significantly enhances tracking performance under frequent occlusion conditions, with the MOTA metric improving from 64.26% to 66.93% and the IDF1 metric improving from 53.73% to 63.70% compared to the baseline algorithm, providing more reliable technical support for underwater fish behavior analysis. Full article

This work presents the synthesis, characterisation, photophysical properties, time-resolved spectroscopic behaviour, and biological evaluation of two structurally distinct heavy-atom-free BODIPY-anthracene dyads (BDP-1) and the newly designed 2,6-bis[1-(tert-butyl) 4-(prop-2-yn-1-yl) piperazine-1,4-dicarboxylate] BODIPY-anthracene (BDP-2), incorporating 2,6-alkynyl-piperazine substituents for potential application in antimicrobial photodynamic therapy. BDP-1 exhibits absorption and emission maxima at 507 nm and 516 nm, respectively, with a Stokes shift of 344 cm⁻¹ in dichloromethane (DCM), characteristic of unsubstituted BODIPYs. In contrast, BDP-2 undergoes a red-shift in the absorption maximum to 552 nm (Stokes shift of 633 cm⁻¹), which is attributed to the extended conjugation from the introduction of the alkyne groups. Time-resolved infrared spectroscopy confirmed efficient spin-orbit charge transfer intersystem crossing, and nanosecond transient absorption studies confirmed the formation of a long-lived triplet state for BDP-2 (up to 138 µs in MeCN). A binding constant (K_b) of 9.6 × 10⁴ M⁻¹ was obtained for BDP-2 when titrated with bovine serum albumin (BSA), which is higher than comparable BODIPY derivatives. BDP-2 displayed improved hemocompatibility compared to BDP-1 (<5% haemolysis of human erythrocytes up to 200 μg·mL⁻¹). Antimicrobial activity of BDP-1 and BDP-2 was most potent when irradiated at 370 nm compared to the other wavelengths employed. However, BDP-2 did not retain the potent (6 log) and rapid (within 15 min) eradication of Staphylococcus aureus achieved by BDP-1 under irradiation at 370 nm. These findings demonstrate the rational design of BDP-2 as a biocompatible, and heavy-atom-free BODIPY offering promise for targeted antimicrobial photodynamic therapeutic applications. Full article

A tetradentate Pt(II) complex with a 5/6/6 structural backbone, Pt(PhPiPy-O-PytmCz), was synthesized by incorporating two distinct cycloalkyl groups. These structural modifications significantly enhanced the photoluminescence quantum yield and effectively increased the distance between molecules, thereby mitigating undesirable intermolecular interactions and triplet-state quenching. This strategic molecular design resulted in an external quantum efficiency of 11.5% at a wavelength of 539 nm and significantly enhanced operational lifetimes in green phosphorescent organic light-emitting diodes (OLEDs). These findings are expected to inspire the development of new green luminescent materials and innovative strategies in OLED technology. Full article

Photosensitizers with high singlet oxygen (¹O₂) generation capacity under near-infrared (NIR) irradiation are essential and challenging for photodynamic therapy (PDT). A simple yet effective molecular design strategy is realized to construct 1 + 1 > 2 photosensitizers with synergistic effects by covalently integrating iridium complexes with cyanine via ether linkages, as well as introducing aldehyde groups to suppress non-radiative decay, named CHO−Ir−Cy. It is demonstrated that CHO−Ir−Cy successfully maintains the NIR absorption and emission originated from cyanine units and high ¹O₂ generation efficiency from the iridium complex part, which gives full play to their respective advantages while compensating for shortcomings. Density functional theory (DFT) calculations reveal that CHO−Ir−Cy exhibits a stronger spin–orbit coupling constant (ξ (S1, T1) = 9.176 cm⁻¹) and a reduced energy gap (ΔE = −1.97 eV) between triplet excited states (T₁) and first singlet excited states (S₁) compared to parent Ir−Cy or Cy alone, directly correlating with its enhanced ¹O₂ production. Remarkably, CHO−Ir−Cy demonstrates superior cellular internalization in 4T1 murine breast cancer cells, generating substantially elevated ¹O₂ yields compared to individual Ir−Cy/Cy under 808 nm laser irradiation. Such enhanced reactive oxygen species production translates into effective cancer cell ablation while maintaining favorable biocompatibility, significant phototoxicity and negligible dark toxicity. This molecular engineering strategy overcomes the inherent NIR absorption limitation of traditional iridium complexes and ensures their own high ¹O₂ generation ability through dye–metal synergy, establishing a paradigm for designing metal–organic photosensitizers with tailored photophysical properties for precision oncology. Full article

Liquid crystals exhibit unique properties that can be tailored in response to external stimuli. Significant research is directed toward the development of luminescent materials exhibiting liquid crystallinity for various applications. The present work reports Au(I) complexes featuring N-heterocyclic carbene and phenyl acetylide ligands. Metal complexes enable the utilization of the triplet excitons through their inherent spin–orbit coupling, promoting intersystem crossing from singlet (S_n) to triplet (T_n) states to observe room-temperature phosphorescence (RTP). The strong bonds between carbene and Au enhance the thermal stability, and the substituted benzimidazole ring alters the thermodynamic and photophysical properties of the complexes. Incorporating the acetylide ligands with long alkoxy chains led to the formation of liquid crystalline (LC) phases, which exhibited stability over a wide temperature range. Additionally, the luminescence behavior was affected by the ethynyl ligands, and high quantum yields of RTP were observed. This study establishes the development of LC Au(I) complexes with a thermodynamically stable LC mesophase over a wide temperature range for applications in the field of light-emitting functional materials. Full article

The demand for polymer composite materials in the dental market is increasing every year. This rise is due to their excellent properties and ongoing technological advancements. The goal of this study was to develop new photoinitiators included in the liquid organic matrix, which is one of the main components of dental composites. Therefore, a series of compounds based on the indenoquinoxaline skeleton was synthesized, differing in the substituent. The spectroscopic properties of these compounds allowed their use as visible-light photoinitiators of radical polymerization in combination with (phenylthio)acetic acid. In addition to the polymerization kinetics, the lifetime and quantum yield of the triplet-state formation and the rate constants of its quenching by (phenylthio)acetic acid were determined. The durability of the designed composites was also assessed. Ageing tests included hydrothermal ageing, allowing for the determination of sorption, solubility, and mass change. Solutions imitating the oral cavity environment—distilled water, artificial saliva, n-heptane, and 3% acetic acid—as well as solutions containing pigments were used for these studies. Determination of the mass change and colour stability allowed for the assessment of how these materials react to long-term exposure in the oral environment. It was found that the solution simulating the natural oral environment has a significant impact on the hydrolytic stability and colour stability of the materials. Full article

N-phenyl-1H-Indole-5-carboxamide (Ind-CA) exhibits previously unknown room-temperature phosphorescence (RTP) when immobilized in poly (vinyl alcohol) film (PVA film). High-fluorescence anisotropy of Ind-CA in PVA suggests that the fluorophores are strongly immobilized in a polymer matrix, while a relatively low (ca. 0.1) quantum yield indicates a strong non-radiative singlet excited state deactivation. With an increased triplet-state population, Ind-CA can be used for various phosphorescence studies. The room-temperature phosphorescence (RTP) capability of Ind-CA indicates that there is an intricate balance between RTP and the structure of the indole-containing luminophore, as an isomeric N-1H-indole-5-ylbenzamide (Ind-BA) does not show any appreciable levels of RTP. Moreover, the phosphorescence lifetime of Ind-CA is about two orders of magnitude longer than many other 5-substituted indoles. These results further highlight the prospects for the potential rational designs of small molecules with desired triplet-state configuration and RTP characteristics. Full article

Photochemical degradation is a major removal pathway for pharmaceutical pollutants in water, and dissolved organic matter (DOM) in water is an important factor affecting this process. This study investigates the differential effects of seasonally-varied dissolved organic matter (DOM) from Songhua River and Liao River on the photodegradation of pharmaceutical pollutants, using levofloxacin (LFX), sulfamethoxazole (SMZ), and ibuprofen (IBP) as target compounds. The results demonstrated that summer and autumn DOM inhibited the photodegradation of LFX and SMZ through light screening and dynamic quenching effects, with inhibition rates of 35.1% and 55.5%, respectively, whereas winter DOM enhanced degradation through photo-oxidation mechanisms. DOM from Songhua River and Liao River significantly promoted the photodegradation of IBP. Quenching experiments showed differences in the contributions of photochemically reactive intermediates (PPRIs) to the photodegradation of different target pollutants, with hydroxyl radicals (•OH) dominating LFX photodegradation (48.79% contribution), excited triplet states of DOM (³DOM*) dominating SMZ photodegradation (85.20% contribution), and singlet oxygen (¹O₂) dominating IBP photodegradation (79.89% contribution). The photodegradation pathways were elucidated by measuring the photodegradation by-products of the target pollutants: LFX mainly underwent piperazine ring cleavage and oxidative decarboxylation, SMZ underwent isoxazole ring opening and deamination during photodegradation, and IBP underwent photodecarboxylation and oxidation reactions. Under the influence of the DOM from the Songhua River and Liao River, the generation of multiple photodegradation by-products led to an increasing trend in the acute toxicity of target pollutants to luminescent bacteria. This investigation elucidates the dual regulatory mechanisms of natural aquatic DOM on both photo-induced degradation pathways and toxicity evolution dynamics of pharmaceutical contaminants, which is of great significance for understanding the photochemical transformation behavior and risk assessment of pharmaceutical pollutants in aquatic environments. Full article

Coupling organic light-harvesting materials with lead halide perovskite quantum dots (LHP QDs) is an attractive approach that could provide great potential in optoelectronic applications owing to the diversity of organic materials available and the intriguing optical and electronic properties of LHP QDs. Here, we demonstrate energy collection by CsPbI₃ QDs from a near-infrared (NIR) light-harvesting upconversion system. The upconversion system consists of Pd-tetrakis-5,10,15,20-(p-methoxycarbonylphenyl)-tetraanthraporphyrin (PdTAP) as the sensitizer to harvest NIR photons and rubrene as the annihilator to generate upconverted photons via triplet fusion. Steady-state and time-resolved photoluminescence spectra reveal that CsPbI₃ QDs are energized via radiative energy transfer from the singlet excited rubrene with photophysics fidelity of respective components. In addition, a volumetric display demo incorporating CsPbI₃ QDs as light emitters employing triplet fusion upconversion was developed, showing bright luminescent images from CsPbI₃ QDs. These results present the feasibility of integrating organic light-harvesting systems and perovskite QDs, enabling diverse light harvesting and activation of perovskite materials for optoelectronic applications. Full article

Ground penetrating radar (GPR) is an effective and efficient nondestructive testing technology for subsurface investigations. Deep learning-based methods have been successfully used in automatic underground target recognition. However, these methods are mostly based on supervised learning, requiring large amounts of labeled training data to guarantee high accuracy and generalization ability, which is a challenge in GPR fields due to time-consuming and labor-intensive data annotation work. To alleviate the demand for abundant labeled data, a semi-supervised deep learning method named attention–temporal ensembling (Attention-TE) is proposed for underground target recognition using GPR B-scan images. This method integrates a semi-supervised temporal ensembling architecture with a triplet attention module to enhance the classification performance. Experimental results of laboratory and field data demonstrate that the proposed method can automatically recognize underground targets with an average accuracy of above 90% using less than 30% of labeled data in the training dataset. Ablation experimental results verify the efficiency of the triplet attention module. Moreover, comparative experimental results validate that the proposed Attention-TE algorithm outperforms the supervised method based on transfer learning and four semi-supervised state-of-the-art methods. Full article

It is experimentally established that there is no ground triplet state of the natural $He$ atom. There is also no exact analytical solution to the Schrödinger equation corresponding to this state. For a two-dimensional two-electron ‘artificial atom’ or a semiconductor quantum dot in a magnetic field, as described by the Schrödinger–Pauli equation, we provide theoretical proof of the existence of a ground triplet state by deriving an exact analytical correlated wave function solution to the equation. The state exists in the Wigner high-electron-correlation regime. We further explain that the solution satisfies all requisite symmetry and electron coalescence constraints of a triplet state. Since, due to technological advances, such a Wigner crystal quantum dot can be created, we propose an experimental search for the theoretically predicted ground triplet-state spectral line. We note that there exists an analytical solution to the Schrödinger–Pauli equation for a ground singlet state in the Wigner regime for the same value of the magnetic field. The significance to quantum mechanics of the probable experimental observation of the ground triplet state for an ‘artificial atom’ is discussed. Full article