A nitrogen-rich Eu-MOF for ultrasensitive fluorescence detection of 6-mercaptopurine and 6-thioguanine.

The efficiency of Eu(3+) luminescence by energy transfer from an antenna ligand can be strongly dependent on the metal ion coordination geometry. The geometric component of the Eu(III) sensitization has been probed using series of tetradentate 1,2-HOPO derivatives that are connected by bridges of varying length and geometry. The ligands are N,N'-(1,2-phenylene)bis(1-hydroxy-6-oxo-1,6-dihydropyridine-2-carboxamide) for the ligand (L(1)), 1-hydroxy-N-(2-(1-hydroxy-6-oxo-1,6-dihydropyridine-2-carboxamido)benzyl)-6-oxo-1,6-dihydropyridine-2-carboxamide (L(2)) and N,N'-(1,2-phenylenebis(methylene))bis(1-hydroxy-6-oxo-1,6-dihydropyridine-2-carboxamide) (L(3)). Spectroscopic characterization of both the Gd(III) and the Eu(III) metal complexes, time-dependent density functional theory (TD-DFT) analysis of model compounds and evaluation of the kinetic parameters for the europium emission were completed. Some striking differences were observed in the luminescence quantum yield by altering the bridging unit. The [Eu(L(2))(2)](-) derivative shows efficient sensitization coupled with good metal centered emission. For [Eu(L(3))(2)](-), the large quenching of the luminescence quantum yield compared to [Eu(L(2))(2)](-) is primarily a result of one inner sphere water molecule bound to the europium cation while for [Eu(L(1))(2)](-), the low luminescence quantum yield can be attributed to inefficient sensitization of the europium ion.

Metal clusters have attracted wide interests due to their unique electronic and optical properties, but the low luminescence quantum yield (QY) prevents them from potential biomedical applications. In this work, silver-doped Au nanoclusters (NCs) are shown to be able to improve the QY of metal clusters. We succeeded in synthesizing ultrabright glutathione (GSH) protected AuAg clusters with 10.8% QY by a one-pot route. Their florescence is about 7.5 times brighter than pure Au NCs, with super photostability and good biocompatibility in physiological environment. Based on density functional theory (DFT) calculations, we investigated the electronic structures and optical properties of the AuAg NCs. The results show that the increase of the density of states of the lowest unoccupied molecular orbital (LUMO) leads to the fluorescence enhancement. In addition, two-photon excitation fluorescence imaging has been performed to show their great potential for biomedicine.

Cyclometalated iridium(III) complexes have been used in various optical materials, including organic light-emitting diodes (OLEDs) and photocatalysts, and a deeper understanding and prediction of their luminescence quantum yields (LQYs) greatly aid in accelerating material design. In this study, we integrated density functional theory (DFT) calculations with machine learning (ML) techniques to extract factors controlling LQY. Although a substantial data set of Ir(III) complexes and their LQYs is indispensable for constructing accurate ML models to predict LQYs, generating this type of data set is challenging due to the complexities associated with ab initio calculations of LQYs. To address this issue, we investigated the nonradiative decay process of nine Ir(III) complexes emitting blue to green, each exhibiting varying experimental LQYs, by using DFT calculations. For all nine complexes, the quenching process was induced by the rotation of the single bond in one of the ligands, which converted the six-coordinate structure to the five-coordinate structure. Since the decay mechanism was common for the nine Ir(III) complexes, parameters correlated with LQYs could be used as objective variables instead of LQYs. Based on this idea, we collected a data set featuring Ir(III) complexes and the energy differences between their six- and five-coordinate triplet structures, which correlated with LQYs. We also constructed ML models using the calculated LQYs as the objective variables with the parameters from the ground-state calculations as explanatory variables. The analyses of the constructed model revealed that the LUMO energy of the ligand made the most significant negative contribution to LQY. This suggests that the potential energy surface of the metal-to-ligand charge transfer (MLCT) excited state, which stabilizes the six-coordinate structure, is reduced by decreasing the energy of the unoccupied orbitals.

Octahedral d(6) low-spin Re(I) tricarbonyl complexes are of considerable interest as noninvasive imaging probes and have been deeply studied owing to their biological stability, low toxicity, large Stokes shifts, and long luminescence lifetimes. We reported recently the bimodal IR and luminescence imaging of a Re(I) tricarbonyl complex with a Pyta ligand (4-(2-pyridyl)-1,2,3-triazole) in cells and labeled such metal-carbonyl complexes SCoMPIs for single-core multimodal probes for imaging. Re(I) tricarbonyl complexes have unique photophysical properties allowing for their unequivocal detection in cells but also present some weaknesses such as a very low luminescence quantum yield in aqueous medium. Further optimizations would thus be desirable. We therefore developed new Re(I) tricarbonyl complexes prepared from different ancillary ligands. Complexes with benzothiadiazole-triazole ligands show interesting luminescent quantum yields in acetonitrile and may constitute valuable luminescent metal complexes in organic media. A series of complexes with bidentate 1-(2-quinolinyl)-1,2,3-triazole (Taquin) and 1-(2-pyridyl)-1,2,3-triazole (Tapy) ligands bearing various 4-substituted alkyl side chains has been designed and synthesized with efficient procedures. Their photophysical properties have been characterized in acetonitrile and in a H2O/DMSO (98/2) mixture and compared with those of the parent Quinta- and Pyta-based complexes. Tapy complexes bearing long alkyl chains show impressive enhancement of their luminescent properties relative to the parent Pyta complex. Theoretical calculations have been performed to further characterize this new class of rhenium tricarbonyl complexes. Preliminary cellular imaging studies in MDA-MB231 breast cancer cells reveal a strong increase in the luminescence signal in cells incubated with the Tapy complex substituted with a C12 alkyl chain. This study points out the interesting potential of the Tapy ligand in coordination chemistry, which has been so far underexploited.

The photophysical properties of lanthanide complexes have been studied extensively; however, fundamental parameters such as the intrinsic quantum yield as well as radiative and nonradiative decay rates are difficult or even impossible to measure experimentally. Herein, a photoacoustic (PA) method is proposed to determine the intrinsic quantum yield of lanthanide complexes with lifetimes in the order of milliseconds. This method is used to determine the intrinsic quantum yields for europium(III)-containing metallomesogens as well as terbium(III) complexes. The results show that the PA signal is sensitive to both the lifetime and the ratio of the fast-to-slow heat component of the samples. It is found that there is an efficient ligand sensitization and a moderate intrinsic quantum yield for the complexes. The intrinsic quantum yield of Eu(3+) in the metallomesogens exhibits an obvious increase upon the isotropic liquid to smectic A transition. The proposed PA method is quite simple, and can contribute to a clearer understanding of the photophysical processes in luminescent lanthanide complexes.

Design and preparation of a multi-responsive Cd-based fluorescent coordination polymer for smart sensing of nitrobenzene and ornidazole

Rare earth ions are the backbone of a wide range of optoelectronic applications, ranging from solid-state lasers and fiber amplifiers to silicon photonics. So far experiments on single rare-earth ions have been elusive because of the long excited state lifetimes and low absorption cross sections. Here we present the first single molecule photoemission study of an endohedral metallofullerene (Y3N@C80). This molecule has a low intrinsic photoluminescence quantum yield and a long radiative lifetime. We find that the Y3N species is rigidly attached to the C80 cage, imparting a fixed absorption dipole moment to the molecule as a whole. To improve the absorption and emission of light, we couple single Y3N@C80 molecules to single gold nanoparticles, which results in a photoluminescence enhancement of 2 orders of magnitude. Such unexpectedly high enhancements are a consequence of the low intrinsic quantum yield of Y3N@C80. Our work paves the way for applications of rare-earth ions on the single emitter level.

Pre-accumulation and in-situ destruction of diclofenac by a photo-regenerable activated carbon fiber supported titanate nanotubes composite material: Intermediates, DFT calculation, and ecotoxicity

A novel strategy is presented for constructing ratiometric fluorescent detection platform based on terbium(Ⅲ) ion as a single luminescence center, enabling sensing of permanganate ions (MnO4‒) in water. The approach leverages the differential quenching mechanisms of MnO4‒ on distinct emission bands of terbium-based metal-organic frameworks (Tb-MOFs), using the intensity ratio of specific emission wavelengths (I548/I622) as the detection signal for MnO4‒ quantification. A ratiometric probe [Tb(BCB)(DMF)]·(DMF)1.5(H2O)2 (H3BCB: 4,4',4''-benzenetricarbonyltribenzoic acid) (1) was developed, demonstrating high selectivity, sensitivity, and anti-interference capability toward MnO4‒. The study of quenching mechanism reveals that the 622nm emission is quenched solely by the inner filter effect (IFE), whereas the 548nm emission undergoes synergistic quenching by IFE and Förster resonance energy transfer (FRET). This differential quenching leads to a distinct decrease in I548/I622, forming a robust ratiometric sensing platform. Notably, the method eliminates interference from dichromate ions (Cr2O72‒). The strategy's generality is validated by a second Tb-MOF ([Tb(cpia)(H2O)2]n·nH2O (H3cpia: 5-(4-carboxyphenoxy) isophthalic acid) (2)), which also functions as a ratiometric probe for MnO4‒. These findings establish a universal design principle for constructing single-luminescence-center ratiometric fluorescence platforms.

One-pot green synthesis of N,S co-doped biomass carbon dots from natural grapefruit juice for selective sensing of Cr(VI)

Rapid Peptide Fragmentation without Electrons, Collisions, Infrared Radiation, or Native Chromophores

On the structural, photophysical and antimicrobial properties of bimetallic Re-Fe coordination compounds bearing diimines ligands.

<p indent="0mm">Lanthanide-doped upconversion nanoparticles (UCNPs) exhibit unique anti-Stokes properties, they absorb low-energy long-wave photons and convert them into high-energy short-wave photons for emission, and UCNPs also possess low toxicity and highly stable chemical properties. However, UCNPs suffer from a small absorption cross section and low luminescence quantum yield, which severely limit their applications in photovoltaic devices and biomedical fields. How to enhance the luminescence performance of UCNPs is crucial for the development of upconversion nanoparticles. Studies have shown that utilizing the surface plasmon (SP) effect to construct a coupling mode between UCNPs and metal nanostructures can enhance and stabilize luminescence efficiency. Building upon the aforementioned theories, our research proposes a nanoarray structure comprising a silicon substrate, a gold layer, a periodic gold pillar nanoarray, and UCNPs. By changing the materials of the cylindrical arrays, optimizing the period of the gold pillar arrays, and adjusting the thickness of the UCNPs, the perfect matching of the <sc>808 nm</sc> excitation wavelength, <sc>450 nm</sc> emission wavelength, and the surface plasmon resonance wavelength of the UCNPs was successfully achieved. This matching results in a significant enhancement of the emission and excitation processes of the UCNPs at the same time. Through numerical simulations, this novel nano-array structure enables the upconversion luminescence enhancement factor of the UCNPs layer to reach 1.4×10⁵, which significantly improves the upconversion luminescence efficiency. This study not only offers an entirely new design concept for plasma structures that combine a simple fabrication process, high absorption efficiency, low energy loss, and excellent control over localized surface plasmon resonance, but also exhibits immense application potential in fields such as photovoltaic devices, photocatalytic reactions, and high-sensitivity biosensing.

A new persistent organic free radical has been synthetized with Br atoms occupying the ortho- and para-positions of a trityl core. After the isolation of its two propeller-like atropisomers, Plus (P) and minus (M), their absolute configurations were assigned by a combination of theoretical and experimental data. Remarkably, no hints of racemization were observed up to 60 °C for more than two hours, due to the higher steric hindrance imposed by the bulky Br atoms. Therefore, when compared to its chlorinated homologue (t1/2 =18 s at 60 °C), an outstanding stability against racemization was achieved. A circularly polarized luminescence (CPL) response of both enantiomers was detected. This free radical shows a satisfactory luminescent dissymmetry factor (|glum (592 nm)|≈0.7×10-3 ) despite its pure organic nature and low luminescence quantum yield (LQY). Improved organic magnetic CPL emitters derived from the reported structure can be envisaged thanks to the wide possibilities that Br atoms at para-positions offer for further functionalization.

Redox-controlled luminescence quenching is presented for a new Ru(II)-bipyridine complex [Ru(bpy)2(1)]2+ where ligand 1 is an anthra[1,10]phenanthrolinequinone. The complex emits from a short-lived metal-to-ligand charge transfer, 3MLCT state (τ = 5.5 ns in deaerated acetonitrile) with a low luminescence quantum yield (5 × 10-4). The emission intensity becomes significantly enhanced when the switchable anthraquinone unit is reduced to corresponding hydroquinone. On the contrary, chemical one-electron reduction of the anthraquinone moiety to semiquinone in aprotic tetrahydrofuran results in total quenching of the emission.