Guest-Responsive Near-Infrared-Luminescent Metal-Organic Cage Organized by Porphyrin Dyes and Yb(III) Complexes.

Metal-organic cages (MOCs) with luminophores have significant advantages for the facile detection of specific molecules based on turn-on or turn-off luminescence changes induced by host-guest complexation. One important challenge is the development of turn-on-type near-infrared (NIR)-luminescent MOCs. In this study, we synthesized a novel MOC consisting of two porphyrin dyes linked by four Yb(III) complexes, which exhibit bimodal red and NIR fluorescence signals upon photoexcitation of the porphyrin π system. Single-crystal X-ray structural analysis and computational molecular modeling revealed that planar aromatic perfluorocarbons were intercalated into the MOC. The tight packing between the MOC and guests enhanced the NIR fluorescence of Yb(III) by suppressing energy transfer from the photoexcited porphyrin to oxygen molecules. Guest-responsive turn-on NIR fluorescence changes in an MOC were successfully demonstrated.

Structure-changeable luminescent Eu(III) complex as a human cancer grade probing system for brain tumor diagnosis.

Accurate determination of human tumor malignancy is important for choosing efficient and safe therapies. Bioimaging technologies based on luminescent molecules are widely used to localize and distinguish active tumor cells. Here, we report a human cancer grade probing system (GPS) using a water-soluble and structure-changeable Eu(III) complex for the continuous detection of early human brain tumors of different malignancy grades. Time-dependent emission spectra of the Eu(III) complexes in various types of tumor cells were recorded. The radiative rate constants (kr), which depend on the geometry of the Eu(III) complex, were calculated from the emission spectra. The tendency of the kr values to vary depended on the tumor cells at different malignancy grades. Between T = 0 and T = 3 h of invasion, the kr values exhibited an increase of 4% in NHA/TS (benign grade II gliomas), 7% in NHA/TSR (malignant grade III gliomas), and 27% in NHA/TSRA (malignant grade IV gliomas). Tumor cells with high-grade malignancy exhibited a rapid upward trend in kr values. The cancer GPS employs Eu(III) emissions to provide a new diagnostic method for determining human brain tumor malignancy.

Controlling Dielectric Film Defects to Increase the Breakdown Voltage of Conductive Polymer Solid Capacitors.

Aluminum solid polymer capacitors are promising devices for the increased demand for power electronics applications. Nonetheless, the low breakdown voltage of commercially available catalysts (∼100 V) limits their applications. In this study, a hydroxide-film-covered high-purity aluminum was anodized at 700 V in boric acid at 85 °C, and the effect of a second hot water immersion (posthydration treatment) after anodizing on the breakdown voltage was studied as a possible future treatment to enhance the withstand voltages of solid electrolytic capacitors. The dielectric breakdown voltage of the anodized aluminum with a PEDOT:PSS coating was ∼500 V, being ∼200 V less than the anodizing voltage; however, the dielectric breakdown voltage was increased above 700 V by introducing the posthydration treatment due to the formation of a nanovoid layer above the dielectric alumina film. Our research suggests that the highly dispersed nanovoids incorporated with PEDOT:PSS avoid the current concentration at some local regions, effectively increasing the dielectric breakdown voltage. The posthydration treatment increased the leakage current by introducing physical defects in the dielectric film. However, the leakage current was reduced by a voltage sweep below the breakdown voltage after the PEDOT:PSS coating or a second anodizing process before the coating, keeping the breakdown voltage above 600 V. A promising processing route to obtain aluminum solid capacitors with high withstand voltage (600 V) found in our research is, first, dipping in hot water; second, anodizing at 700 V; then a second hot water treatment; and a second anodizing at 400 V, which keeps the capacitance invariable with a breakdown voltage enhanced.

Sandglass-Typed Single Chameleon Luminophore for Water Mapping Measurements: Intramolecular Energy Migrations in the Hydrophilic Tb(III)/Sm(III) Cluster.

Novel hydrophilic and color-changeable single chameleon luminophores composed of Tb(III)/Sm(III) nona-nuclear clusters [TbxSm9-x(Sal-PEG-n)16(µ-OH)10]+(NO3)- (x = 1, 2, 3, and 9; Sal-PEG-n: salicylate polyethylene glycolmethylester, n = 2 and 4) are reported for water mapping measurements. Their characteristic sandglass structures and aggregates were analyzed using X-ray single crystal analysis and dynamic light scattering (DLS) measurements. The green- and yellow-luminescence of [Tb3Sm6(Sal-PEG-4)16(µ-OH)]+(NO3)- in water were observed at 20 and 50 °C, respectively. The ratio-metric luminescence analysis using green Tb(III) and orange Sm(III) emission bands is a promising candidate for exact temperature distribution measurements in fluid dynamics. The effective temperature-sensing property based on the competitive intramolecular energy transfer processes between Tb(III)-to-ligand and Tb(III)-to-Sm(III) in a non-a-nuclear cluster is explained using temperature-dependent kinetic analyses in the excited state.

Thermally-assisted photosensitized emission in a trivalent terbium complex.

Luminescent lanthanide complexes containing effective photosensitizers are promising materials for use in displays and sensors. The photosensitizer design strategy has been studied for developing the lanthanide-based luminophores. Herein, we demonstrate a photosensitizer design using dinuclear luminescent lanthanide complex, which exhibits thermally-assisted photosensitized emission. The lanthanide complex comprised Tb(III) ions, six tetramethylheptanedionates, and phosphine oxide bridge containing a phenanthrene frameworks. The phenanthrene ligand and Tb(III) ions are the energy donor (photosensitizer) and acceptor (emission center) parts, respectively. The energy-donating level of the ligand (lowest excited triplet (T1) level = 19,850 cm-1) is lower than the emitting level of the Tb(III) ion (5D4 level = 20,500 cm-1). The long-lived T1 state of the energy-donating ligands promoted an efficient thermally-assisted photosensitized emission of the Tb(III) acceptor (5D4 level), resulting in a pure-green colored emission with a high photosensitized emission quantum yield (73%).

Characteristic stacked structures and luminescent properties of dinuclear lanthanide complexes with pyrene units.

A novel design strategy of stacked organic fluorophores using dinuclear lanthanide (Ln(III)) complexes is demonstrated for the formation of excimer. The dinuclear Ln(III) complexes are composed of two Ln(III) (Eu(III) or Gd(III)) ions, six hexafluoroacetylacetonate (hfa), and two pyrene-based phosphine oxide ligands. Single-crystal analysis revealed a rigid pyrene-stacked structure via CH-F (pyrene/hfa) intramolecular interactions. The rigid aggregation structures of the two-typed organic ligands around Ln(III) resulted in high thermal stability (decomposition temperature: 340°C). The aggregated ligands exhibited excimer-type green emission from the stacked pyrene-center. The change in the Ln(III) ion promotes effective shifts of excimer emissions (Gd(III):500 nm, Eu(III):490 nm). The organic aggregation system using red-luminescent Eu(III) also provides temperature-sensitive ratiometric emission composed of π-π* and 4f-4f transitions by energy migration between aggregated ligands and Eu(III).

Molecular Weight-Dependent Oxidation and Optoelectronic Properties of Defect-Free Macrocyclic Poly(3-hexylthiophene).

The redox behaviors of macrocyclic molecules with an entirely π-conjugated system are of interest due to their unique optical, electronic, and magnetic properties. In this study, defect-free cyclic P3HT with a degree of polymerization (DPn) from 14 to 43 was synthesized based on our previously established method, and its unique redox behaviors arising from the cyclic topology were investigated. Cyclic voltammetry (CV) showed that the HOMO level of cyclic P3HT decreases from -4.86 eV (14 mer) to -4.89 eV (43 mer), in contrast to the linear counterparts increasing from -4.94 eV (14 mer) to -4.91 eV (43 mer). During the CV measurement, linear P3HT suffered from electro-oxidation at the chain ends, while cyclic P3HT was stable. ESR and UV-Vis-NIR spectroscopy suggested that cyclic P3HT has stronger dicationic properties due to the interactions between the polarons. On the other hand, linear P3HT showed characteristics of polaron pairs with multiple isolated polarons. Moreover, the dicationic properties of cyclic P3HT were more pronounced for the smaller macrocycles.

Enhanced circularly polarized luminescence of chiral Eu(III) coordination polymers with structural strain.

Three types of Eu(III) coordination polymers with different distorted chiral ligands, [Eu(+tfc)3(p-dpeb)]n, [Eu(+pfc)3(p-dpeb)]n, and [Eu(+hfc)3(p-dpeb)]n (+tfc: (+)-3-(trifluoroacetyl)camphorate, +pfc: (+)-3-(pentafluoropropionyl)camphorate, +hfc: (+)-3-(heptafluorobutyryl)camphorate, p-dpeb: 1,4-bis(diphenylphosphorylethynyl)benzene), were prepared for elucidating the relationship between their structural distortions, ligand-to-metal charge transfer (LMCT), and circularly polarized luminescence (CPL) properties. Their strain factors in the ligands were evaluated using crystallographic data obtained by single-crystal X-ray structural analyses. The characteristics of the LMCT excited states were estimated from theoretical calculations. The introduction of a bulky substituent into the chiral ligand afforded a distorted structure of ß-diketonates and changed the direction of the transition electric dipole moments, which are related to the magnitude of the CPL intensity. The CPL dissymmetry factor (gCPL) of [Eu(+hfc)3(p-dpeb)]n, with a large distorted structure, was -0.22, while those of [Eu(+tfc)3(p-dpeb)]n and [Eu(+pfc)3(p-dpeb)]n, with small distorted structures, were -0.05 and -0.10, respectively. The controlled steric hindrance of the chiral ligands in Eu(III) coordination polymers is one of the strain factors enhancing their CPL properties.

Plant growth acceleration using a transparent Eu3+-painted UV-to-red conversion film.

The stimulation of photosynthesis is a strategy for achieving sustainable plant production. Red light is useful for plant growth because it is absorbed by chlorophyll pigments, which initiate natural photosynthetic processes. Ultraviolet (UV)-to-red wavelength-converting materials are promising candidates for eco-friendly plant cultures that do not require electric power. In this study, transparent films equipped with a UV-to-red wavelength-converting luminophore, the Eu3+ complex, were prepared on commercially available plastic films for plant growth experiments. The present Eu3+-based films absorb UV light and exhibit strong red luminescence under sunlight. Eu3+-painted films provide significant growth acceleration with size increment and biomass production for vegetal crops and trees in a northern region. The plants cultured with Eu3+-painted films had a 1.2-fold height and 1.4-fold total body biomass than those cultures without the Eu3+ luminophores. The present film can promote the plant production in fields of agriculture and forestry.

Effective Photosensitization in Excited-State Equilibrium: Brilliant Luminescence of TbIII Coordination Polymers Through Ancillary Ligand Modifications.

Invited for this month's cover are the collaborating groups of Yuichi Kitagawa, Yasuchika Hasegawa, Tetsuya Taketsugu, and co-workers at Hokkaido University. The cover picture shows a photosensitizer that has a long excited-state lifetime and provides strong emissions for TbIII coordination polymers. The photosensitization ability can be considerably altered by changing the ancillary ligands in the TbIII coordination polymers. The results provide new insights on the design of photosensitizers for improving the properties of photo-functional materials. More information can be found in the Research Article by Y. Kitagawa, Y. Hasegawa, and co-workers.

Preparation of photonic molecular trains via soft-crystal polymerization of lanthanide complexes.

Soft-crystals are defined as flexible molecular solids with highly ordered structures and have attracted attention in molecular sensing materials based on external triggers and environments. Here, we show the soft-crystal copolymerization of green-luminescent Tb(III) and yellow-luminescent Dy(III) coordination centers. Soft-crystal polymerization is achieved via transformation of monomeric dinuclear complexes and polymeric structures with respect to coordination number and geometry. The structural transformation is characterized using single-crystal and powder X-ray diffraction. The connected Tb(III) crystal-Dy(III) crystal show photon energy transfer from the Dy(III) centre to the Tb(III) centre under blue light excitation (selective Dy(III) centre excitation: 460 ± 10 nm). The activation energy of the energy transfer is estimated using the temperature-dependent emission lifetimes and emission quantum yields, and time-dependent density functional theory (B3LYP) calculations. Luminescence-conductive polymers, photonic molecular trains, are successfully prepared via soft-crystal polymerization on crystal media with remarkable long-range energy migration.

Effective Photosensitization in Excited-State Equilibrium: Brilliant Luminescence of TbIII Coordination Polymers Through Ancillary Ligand Modifications.

Molecular photosensitizers provide efficient light-absorbing abilities for photo-functional materials. Herein, effective photosensitization in excited-state equilibrium is demonstrated using five TbIII coordination polymers. The coordination polymers are composed of TbIII ions (emission center), hexafluoroacetylacetonato (photosensitizer ligands), and phosphine oxide-based bridges (ancillary ligands). The two types of ligand combinations induces a rigid coordination structure via intermolecular interactions, resulting in high thermal stability (with decomposition temperatures above 300 °C). Excited-triplet-state lifetimes of photosensitizer ligands (τ=120-1320 µs) are strongly dependent on the structure of the ancillary ligands. The photosensitizer with a long excited-triplet-state lifetime (τ≥1120 µs) controls the excited state equilibrium between the photosensitizer and TbIII , allowing the construction of TbIII coordination polymer with high TbIII emission quantum yield (≥70 %).

Asymmetric Lumino-Transformer: Circularly Polarized Luminescence of Chiral Eu(III) Coordination Polymer with Phase-Transition Behavior.

A chiral Eu(III) coordination polymer with phase-transition behavior, [Eu(+tfc)3(m-dpeb)]n, (+tfc: (+)-3-trifluoroacetylcamphorato, m-dpeb: 1,3-bis(diphenylphosphorylethynyl)benzene) was reported for understanding the effect of polymer chain arrangement (orientation effect) on the circularly polarized luminescence (CPL) in a solid system. The phase-transition behavior of the transformable Eu(III) coordination polymer was characterized using differential scanning calorimetry and powder X-ray diffraction. The Eu(III) coordination polymer exhibited phase transition at approximately 180 °C. The magnitude of the CPL intensity was drastically changed because of the phase transition, without coordination geometrical change around the Eu(III) ion. In this study, the orientation effect of a chiral Eu(III) coordination polymer on the CPL properties in crystalline solid is demonstrated.

Tribo-Excited Chemical Reaction Using an EuIII Complex with a Stacked Anthracene Framework.

Invited for the cover of this issue are Yuichi Kitagawa, Yasuchika Hasegawa, and co-workers at Hokkaido University. The image depicts tribo-excited chemical reaction using trivalent lanthanide complexes with stacked anthracene ligands. Read the full text of the article at 10.1002/chem.202104401.

Tribo-Excited Chemical Reaction Using an EuIII Complex with a Stacked Anthracene Framework.

A spin-selective tribo-chemical reaction using a dinuclear lanthanide complex is demonstrated for the first time. The dinuclear complex is composed of two EuIII ions, hexafluoroacetylacetonato ligands, and anthracene-based phosphine oxide bridges. Single-crystal analysis revealed a face-to-face-type anthracene dimer structure in the dinuclear EuIII complex. Mechanical stimulus on the dinuclear EuIII complex induced selective formation of oxidized anthracene. The tribo-chemical reaction is based on a characteristic energy-transfer pathway for the selective formation of an excited triplet state.

Hybrid EuIII Coordination Luminophore Standing on Two Legs on Silica Nanoparticles for Enhanced Luminescence.

In this study, we have demonstrated a two-legged, upright molecular design method for monochromatic and bright red luminescent LnIII -silica nanomaterials. A novel EuIII -silica hybrid nanoparticle was developed by using a doubly binding TPPO-Si(OEt)3 (TPPO: triphenyl phosphine oxide) linker. The TPPO-Si(OEt)3 was confirmed by 1 H, 31 P, 29 Si NMR spectroscopy and single-crystal X-ray analysis. Luminescent Eu(hfa)3 and Eu(tfc)3 moieties (hfa: hexafluoroacetylacetonate, tfc: 3-(trifluoromethylhydroxymethylene)camphorate) were fixed onto TPPO-Si(OEt)3 -modified silica nanoparticles, producing Eu(hfa)3 (TPPO-Si)2 -SiO2 and Eu(tfc)3 (TPPO-Si)2 -SiO2 , respectively. Eu(hfa)3 (TPPO-Si)2 -SiO2 exhibited the higher intrinsic luminescence quantum yield (93 %) and longer emission lifetime (0.98 ms), which is much larger than those of previously reported EuIII -based hybrid materials. Eu(tfc)3 (TPPO-Si)2 -SiO2 showed an extra-large intrinsic emission quantum yield (54 %), although the emission quantum yield for the precursor Eu(tfc)3 (TPPO-Si(OEt)3 )2 was found to be 39 %. These results confirmed that the TPPO-Si(OEt)3 linker is a promising candidate for development of EuIII -based luminescent materials.

Long-lived emission beyond 1000 nm: control of excited-state dynamics in a dinuclear Tb(III)-Nd(III) complex.

A long-lived near-infrared Nd(iii) emission is demonstrated using a Tb(iii) donor. The observed emission lifetime of 290 µs at 1057 nm for a Tb(iii)-Nd(iii) dinuclear complex is attributed to the long-lived Tb(iii) donor and the appropriate spacing between the lanthanide ions. This design strategy leads to novel lanthanide photophysics.

Coordination Geometrical Effect on Ligand-to-Metal Charge Transfer-Dependent Energy Transfer Processes of Luminescent Eu(III) Complexes.

Photophysical properties of europium (Eu(III)) complexes are affected by ligand-to-metal charge transfer (LMCT) states. Two luminescent Eu(III) complexes with three tetramethylheptadionates (tmh) and pyridine (py), [Eu(tmh)3(py)1] (seven-coordinated monocapped-octahedral structure) and [Eu(tmh)3(py)2] (eight-coordinated square antiprismatic structure), were synthesized for geometrical-induced LMCT level control. Distances between Eu(III) and oxygen atoms of tmh ligands were estimated using single-crystal X-ray analyses. The contribution percentages of π-4f mixing in HOMO and LUMO at the optimized structure in the ground state were calculated using DFT (LC-BLYP). The Eu-O distances and their π-4f mixed orbitals affect the energy level of LMCT states in Eu(III) complexes. The LMCT energy level of an eight-coordinated Eu(III) complex was higher than that of a seven-coordinated Eu(III) complex. The energy transfer processes between LMCT and Eu(III) ion were investigated using temperature-dependent and time-resolved emission lifetime measurements of 5D0 → 7FJ transitions of Eu(III) ions. In this study, the LMCT-dependent energy transfer processes of seven- and eight-coordinated Eu(III) complexes are demonstrated for the first time.

Bright sky-blue fluorescence with high color purity: assembly of luminescent diphenyl-anthracene lutetium-based coordination polymer.

Pure sky-blue fluorescence (FWHM: 50 nm) from lutetium-based coordination polymer with diphenyl-anthracene derivative is demonstrated for the first time. The observed high color purity is based on the tightly packed crystal structure of the coordination polymer with multiple CH-F interactions.

First Tribo-Excited Chemical Reaction of a Stacked Lanthanide Coordination Polymer with an in Situ Reaction Monitor.

A tribo-excited chemical reaction using a stacked lanthanide coordination polymer is demonstrated for the first time. The polymer is composed of a EuIII ion, hexafluoroacetylacetonato ligands, and an anthracene-based phosphine oxide bridge. The tightly stacked structure with hydrogen bonding was characterized by X-ray crystal structure analysis. The mechanical stimulus leads to tribo-excited oxidation in the EuIII coordination polymer. Electron ionization mass spectroscopy and photo-spectroscopic analysis reveal that the chemical product afforded by tribo-oxidation is different from that obtained by photo-oxidation.