Luminescent Ln3+-based silsesquioxanes with a ß-diketonate antenna ligand: toward the design of efficient temperature sensors.

We report the synthesis and single-crystal X-ray diffraction, magnetic, and luminescence measurements of a novel family of luminescent cage-like tetranuclear silsesquioxanes (PhSiO1.5)8(LnO1.5)4(O)(C5H8O2)6(EtOH)2(CH3CN)2⋅2CH3CN (where Ln = Tb, 1; Tb/Eu, 2; and Gd, 3), featuring seven-coordinated lanthanide ions arranged in a one-capped trigonal prism geometry. Compounds 1 and 2 exhibit characteristic Tb3+ and Tb3+/Eu3+-related emissions, respectively, sensitized by the chelating antenna acetylacetonate (acac) ligands upon excitation in the UV and visible spectral regions. Compound 3 is used to assess the energies of the triplet states of the acac ligand. For compound 1, theoretical calculations on the intramolecular energy transfer and multiphonon rates indicate a thermal balance between the 5D4 Stark components, while the mixed Tb3+/Eu3+ analog 2, with a Tb:Eu ratio of 3:1, showcases intra-cluster Tb3+-to-Eu3+ energy transfer, calculated theoretically as a function of temperature. By utilizing the intensity ratio between the 5D4→7F5 (Tb3+) and 5D0→7F2 (Eu3+) transitions in the range 11-373 K, we demonstrate the realization of a ratiometric luminescent thermometer with compound 2, operating in the range 11-373 K with a maximum relative sensitivity of 2.0% K-1 at 373 K. These findings highlight the potential of cage-like silsesquioxanes as versatile materials for optical sensing-enabled applications.

Insights into NdIII to YbIII Energy Transfer and Its Implications in Luminescence Thermometry.

This work challenges the conventional approach of using NdIII 4F3/2 lifetime changes for evaluating the experimental NdIII → YbIII energy transfer rate and efficiency. Using near-infrared (NIR) emitting Nd:Yb mixed-metal coordination polymers (CPs), synthesized via solvent-free thermal grinding, we demonstrate that the NdIII [2H11/2 → 4I15/2] → YbIII [2F7/2 → 2F5/2] pathway, previously overlooked, dominates energy transfer due to superior energy resonance and J-level selection rule compatibility. This finding upends the conventional focus on the NdIII [4F3/2 → 4I11/2] → YbIII [2F7/2 → 2F5/2] transition pathway. We characterized Nd0.890Yb0.110(BTC)(H2O)6 as a promising cryogenic NIR thermometry system and employed our novel energy transfer understanding to perform simulations, yielding theoretical thermometric parameters and sensitivities for diverse Nd:Yb ratios. Strikingly, experimental thermometric data closely matched the theoretical predictions, validating our revised model. This novel perspective on NdIII → YbIII energy transfer holds general applicability for the NdIII/YbIII pair, unveiling an important spectroscopic feature with broad implications for energy transfer-driven materials design.

Morphology does not matter: WSe2 luminescence nanothermometry unravelled.

Transition metal dichalcogenides, including WSe2, have gained significant attention as promising nanomaterials for various applications due to their unique properties. In this study, we explore the temperature-dependent photoluminescent properties of WSe2 nanomaterials to investigate their potential as luminescent nanothermometers. We compare the performance of WSe2 quantum dots and nanorods synthesized using sonication synthesis and hot injection methods. Our results show a distinct temperature dependence of the photoluminescence, and conventional ratiometric luminescence thermometry demonstrates comparable relative thermal sensitivity (0.68-0.80% K-1) and temperature uncertainty (1.3-1.5 K), irrespective of the morphology of the nanomaterials. By applying multiple linear regression to WSe2 quantum dots, we achieve enhanced thermal sensitivity (30% K-1) and reduced temperature uncertainty (0.1 K), highlighting the potential of WSe2 as a versatile nanothermometer for microfluidics, nanofluidics, and biomedical assays.

Exploring the Luminescence, Redox, and Magnetic Properties in a Multivariate Metal-Organic Radical Framework.

Persistent neutral organic radicals are excellent building blocks for the design of functional molecular materials due to their unique electronic, magnetic, and optical properties. Among them, triphenylmethyl radical derivatives have attracted a lot of interest as luminescent doublet emitters. Although neutral organic radicals have been underexplored as linkers for building metal-organic frameworks (MOFs), they hold great potential as organic elements that could introduce additional electronic properties within these frameworks. Herein, we report the synthesis and characterization of a novel multicomponent metal-organic radical framework (PTMTCR@NR-Zn MORF), which is constructed from the combination of luminescent perchlorotriphenylmethyl tricarboxylic acid radical (PTMTCR) and nonemissive nonradical (PTMTCNR) organic linkers and Zn(II) ions. The PTMTCR@NR-Zn MORF structure is layered with microporous one-dimensional channels embedded within these layers. Kelvin probe force microscopy further confirmed the presence of both organic nonradical and radical linkers in the framework. The luminescence properties of the PTMTCR ligand (first studied in solution and in the solid state) were maintained in the radical-containing PTMTCR@NR-Zn MORF at room temperature as fluorescence solid-state quenching is suppressed thanks to the isolation of the luminescent radical linkers. In addition, magnetic and electrochemical properties were introduced to the framework due to the incorporation of the paramagnetic organic radical ligands. This work paves the way for the design of stimuli-responsive hybrid materials with tunable luminescence, electrochemical, and magnetic properties by the proper combination of closed- and open-shell organic linkers within the same framework.

Probing the Protein Folding Energy Landscape: Dissociation of Amyloid-ß Fibrils by Laser-Induced Plasmonic Heating.

Insoluble amyloid fibrils made from proteins and peptides are difficult to be degraded in both living and artificial systems. The importance of studying their physical stability lies primarily with their association with human neurodegenerative diseases, but also owing to their potential role in multiple bio-nanomaterial applications. Here, gold nanorods (AuNRs) were utilized to investigate the plasmonic heating properties and dissociation of amyloid-ß fibrils formed by different peptide fragments (Aß16-22/Aß25-35/Aß1-42) related to the Alzheimer's disease. It is demonstrated that AuNRs were able to break mature amyloid-ß fibrils from both the full length (Aß1-42) and peptide fragments (Aß16-22/Aß25-35) within minutes by triggering ultrahigh localized surface plasmon resonance (LSPR) heating. The LSPR energy absorbed by the amyloids to unfold and move to higher levels in the protein folding energy landscape can be measured directly and in situ by luminescence thermometry using lanthanide-based upconverting nanoparticles. We also show that Aß16-22 fibrils, with the largest persistence length, displayed the highest resistance to breakage, resulting in a transition from rigid fibrils to short flexible fibrils. These findings are consistent with molecular dynamics simulations indicating that Aß16-22 fibrils possess the highest thermostability due to their highly ordered hydrogen bond networks and antiparallel ß-sheet orientation, hence affected by an LSPR-induced remodeling rather than melting. The present results introduce original strategies for disassembling amyloid fibrils noninvasively in liquid environment; they also introduce a methodology to probe the positioning of amyloids on the protein folding and aggregation energy landscape via nanoparticle-enabled plasmonic and upconversion nanothermometry.

Lanthanide-based logic: a venture for the future of molecular computing.

Managing the continuous and fast-growing volume of information, the progress in the Internet-of-Things, and the evolution from digitalization to networking are huge technological chores. Si-based integrated chips face increasing demands as they strive to meet these challenges. However, there is growing recognition that information processing and computing based on molecules performing logic operations may play a decisive role in shaping the future of the computer industry. Molecular logic gates are molecular counterparts of electronic devices that, instead of exclusively by electrical signals, can be stimulated by diverse chemical or physical input signals that produce optical outputs according to a well-defined logical transfer function. Several materials have been applied for molecular logic, however, the Ln3+-based ones appear to be a commendable choice, as they can respond to both chemical and physical stimuli, presenting unique photophysical properties that make them quite popular for photonics applications. Here we critically review illustrative molecular logic systems based on Ln3+ ions and discuss their potential for integration in future molecular photonic-electronic hybrid logic computing systems.

Tunable Optical Molecular Thermometers Based on Metallacrowns.

The effect of ligands' energy levels on thermal dependence of lanthanide emission was examined to create new molecular nanothermometers. A series of Ln2Ga8L8'L8″ metallacrowns (shorthand Ln2L8'), where Ln = Gd3+, Tb3+, or Sm3+ (H3L' = salicylhydroxamic acid (H3shi), 5-methylsalicylhydroxamic acid (H3mshi), 5-methoxysalicylhydroxamic acid (H3moshi), and 3-hydroxy-2-naphthohydroxamic acid (H3nha)) and H2L″ = isophthalic acid (H2iph), was synthesized and characterized. Within the series, ligand-centered singlet state (S1) energy levels ranged from 23,300 to 27,800 cm-1, while triplet (T1) energy levels ranged from 18,150 to 21,980 cm-1. We demonstrated that the difference between T1 levels and relevant energies of the excited 4G5/2 level of Sm3+ (17,800 cm-1) and 5D4 level of Tb3+ (20,400 cm-1) is the major parameter controlling thermal dependence of the emission intensity via the back energy transfer mechanism. However, when the energy difference between S1 and T1 levels is small (below 3760 cm-1), the S1 → T1 intersystem crossing (and its reverse, S1 ← T1) mechanism contributes to the thermal behavior of metallacrowns. Both mechanisms affect Ln3+-centered room-temperature quantum yields with values ranging from 2.07(6)% to 31.2(2)% for Tb2L8' and from 0.0267(7)% to 2.27(5)% for Sm2L8'. The maximal thermal dependence varies over a wide thermal range (ca. 150-350 K) based on energy gaps between relevant ligand-based and lanthanide-based electronic states. By mixing Tb2moshi8' with Sm2moshi8' in a 1:1 ratio, an optical thermometer with a relative thermal sensitivity larger than 3%/K at 225 K was created. Other temperature ranges are also accessible with this approach.

Luminescence thermometry in a Dy4 single molecule magnet.

The tetranuclear linear complex [Dy4(1,1,4-H3Lr)2(OAc)6]·CH3OH (1·CH3OH) was satisfactorily prepared and characterized. Its X-ray structure shows that it contains two types of octacoordinated DyIII ions, with distorted triangular dodecahedral and square antiprism geometries. This complex is an SMM, with multiple relaxation pathways, and with an anisotropic energy barrier of 39.7 K. 1·CH3OH also operates as a luminescent thermometer in the 11-295 K range, with a maximum relative thermal sensitivity of 1.6% K-1 and a minimum temperature uncertainty of 1.1 K at 295 K. Thus, 1·CH3OH is the first Dy4 SMM with luminescent thermometry, and this system is a rare example of dysprosium SMM that accesses the thermometric characteristics involving the ligand ascribed to the triplet emission in combination with DyIII emission.

[Ga3+ 8 Sm3+ 2 , Ga3+ 8 Tb3+ 2 ] Metallacrowns are Highly Promising Ratiometric Luminescent Molecular Nanothermometers Operating at Physiologically Relevant Temperatures.

Nanothermometry is the study of temperature at the submicron scale with a broad range of potential applications, such as cellular studies or electronics. Molecular luminescent-based nanothermometers offer a non-contact means to record these temperatures with high spatial resolution and thermal sensitivity. A luminescent-based molecular thermometer comprised of visible-emitting Ga3+ /Tb3+ and Ga3+ /Sm3+ metallacrowns (MCs) achieved remarkable relative thermal sensitivity associated with very low temperature uncertainty of Sr =1.9 % K-1 and δT<0.045 K, respectively, at 328 K, as an aqueous suspension of polystyrene nanobeads loaded with the corresponding MCs. To date, they are the ratiometric molecular nanothermometers offering the highest level of sensitivity in the physiologically relevant temperature range.

Protein Cohabitation: Improving the Photochemical Stability of R-Phycoerythrin in the Solid State.

The poor photochemical stability of R-phycoerythrin (R-PE) has been a bottleneck for its broad-spectrum applications. Inspired by nature, we studied a sustainable strategy of protein cohabitation to enhance R-PE stability by embedding it in a solid matrix of gelatin. Both pure R-PE and fresh phycobiliprotein (PBP) extracts recovered from Gracilaria gracilis were studied. The incorporation of R-PE in the gelatin-based films (gelatin-RPE and gelatin-PBPs) has improved its photochemical stability for at least 8 months, the longest time period reported so far. These results were evidenced by not only absorption but also emission quantum yield measurements (Φ). Moreover, the photostability of gelatin-RPE films upon continuous excitation with an AM1.5G solar simulator was tested and found to remain stable for 23 h after initial decreasing up to 250 min. In the end, another approach was established to allow 100% photostability for a 3 h exposure to an AM1.5G solar simulator by doping the gelatin-based film including R-Phycoerythrin with n-propyl gallate stabilized with Tween 80, allowing their use as naturally based optically active centers in photovoltaic applications.

High pressure luminescence of Nd3+ in YAlO3 perovskite nanocrystals: A crystal-field analysis.

Pressure-induced energy blue- and red-shifts of the 4F3/2 → 4I9/2,11/2 near-infrared emission lines of Nd3+ ions in YAlO3 perovskite nano-particles have been measured from ambient conditions up to 29 GPa. Different positive and negative linear pressure coefficients have been calibrated for the emission lines and related to pressure-induced changes in the interactions between those Nd3+ ions and their twelve oxygen ligands at the yttrium site. Potentiality of the simple overlap model, combined with ab initio structural calculations, in the description of the effects of these interactions on the energy levels and luminescence properties of the optically active Nd3+ ion is emphasized. Simulations show how the energies of the 4f3 ground configuration and the barycenters of the multiplets increase with pressure, whereas the Coulomb interaction between f-electrons decreases and the crystal-field strength increases. All these effects combined explain the wavelength blue-shifts of some near-infrared emission lines of Nd3+ ions. Large pressure rates of various emission lines suggest that a YAlO3 perovskite nano-crystal can be a potential candidate for near-infrared optical pressure sensors.