Lanthanide-Oligomeric Brush Films: From Luminescence Properties to Structure Resolution

Lanthanide (Ln) based luminescent materials are experiencing an increasing interest in their applications in several fields. In this study, we report a series of new lanthanide-oligomeric brush films, supported on quartz substrates and prepared using a layer-by-layer method (LbL). Oligomeric brush films are composed of small oligomers from our previously reported coordination polymers [x-EuL] and [x-TbL] (with x = 1, 3, and 5 generations of Ln complexes), which are grown perpendicularly from a carboxylate self-assembled monolayer. Oligomers composed of our previously described helical lanthanide complex LnL (Ln: Eu and Tb) as a luminescent moiety and benzene-1,4-dicarboxylate acid (bdc) used as a linker. Mixed films having the fifth-generation Ln complexes composed of equimolar mixture of Eu and Tb ions were prepared. Oligomeric brush films are highly transparent and exhibited a colored emission under UV irradiation. Pure Ln (Eu or Tb) films showed a strong luminescence from the Ln ions. Their luminescent properties depended on the number of lanthanide layers in the films composed of the first to third generations of lanthanide complexes. Then, the increase of the complex layers induced no difference in the luminescent properties. An energy transfer from Tb to Eu ions in the mixed films indicated a short distance between lanthanide ions of a fifth layer. The structural analysis together with the observed luminescent properties and some previous studies allowed to clarify the disposition of the oligomers in the films.

Multicolor upconversion luminescence of dye-coordinated Er3+ at the interface of Er2O3 and CaF2 nanoparticles

Multicolor upconversion luminescence of Er³⁺ was successfully enhanced by optimizing the interface in dye-coordinated nanoparticles with a core/shell structure. Red and green upconversion emissions of Er³⁺ were obtained at the interface of oxide nanoparticles via the intramolecular energy transfer from the coordinating squaraine dye with high light-absorption ability, which was more efficient than emissions through the energy transfer from metal ions such as Yb³⁺. Additionally, CaF₂ nanoparticles as a core material minimized the energy loss with nonradiative downward relaxations in Er³⁺, resulting in the observation of unusual blue upconversion emissions from the upper energy level of Er³⁺ by nonlaser excitation using a continuous-wave (CW) Xe lamp at an excitation power of 1.2 mW/cm².

Europium amphiphilic naphthalene based complex for the enhancement of linearly polarized luminescence in Langmuir–Blodgett films

The complexation in LB films induces the linearly polarized luminescence of europium by the excited 1-naphtoate ligand.

Gelation and luminescence of lanthanide hydrogels formed with deuterium oxide

Gel formations and efficient lanthanide luminescence appeared in deuterium oxide (D₂O) medium instead of light water (H₂O), and their solvation possibilities by using luminescence lifetimes were discussed. The lanthanide ions in the hydrogel of 1 obtained by H₂O (abbreviated as H₂O-Ln1; Ln = Eu, Tb, and Gd) in our previous report act as the coupling part between neighbor molecules for the bundle structure. Here, D₂O also acts as a medium to form the lanthanide-hydrogel of 1, and increases intensities of luminescence for Tb, because a soft crystalline state reducing resonance thermal relaxation is realized. The gel-formation and luminescence band positions of Ln1 in D₂O corresponded to those in H₂O. From the observation of luminescence lifetimes in H₂O and D₂O, the number of coordinating water molecules on Eu and Tb were estimated to be around 3 or 4 for both. The luminescence intensity of Eu1 did not increase even in D₂O, due to a blue shift of the excited triplet state of 1, as compared to that in H₂O.

Luminescent lanthanide hydrogels using the low-molecular weight gelator 1 in D₂O were developed and evaluated quantitatively.

Phosphorescence Resulting from Interaction between Two Non-equivalent Metals on a Helical π-Conjugated Surface

A [7]helicene bis-ruthenium complex, with one ruthenium atom bound to the cyclopentadienyl (Cp) ring and the other coordinated to the arene ring at the edge of the helicene, was synthesized. This complex showed phosphorescence both in butyronitrile (Φ=31 %, 77 K) and in the solid state (Φ=18 %, 77 K). The two non-equivalent ruthenium metal atoms, attached to the helicene ligand, interact with each other upon photoabsorption and emission.

Sensitive Photodetection with Photomultiplication Effect in an Interfacial Eu2+/3+ Complex on a Mesoporous TiO2 Film

A simple device structure composed of an interfacial Eu^2+/3+ complex on a mesoporous TiO₂ film is developed by a solution process and acts as the high-performance photodetector with photomultiplication phenomena. The electron transfer from the photoexcited organic ligand, 2,2':6',2″-terpyridine (terpy), as a photosensitizer to TiO₂ is accelerated by the reduction level of Eu^3+/2+ ions chemically bonding among terpy and TiO₂, resulting in the generation of a large photocurrent. It is worth noting that its external quantum efficiency is in excess of 10⁵% under applied reverse bias. The corresponding responsivity of the device is also determined to be 464 A/W at an irradiation light intensity of 0.7 mW/cm² (365 nm), which is more than 3 orders of magnitude larger than those of inorganic photodetectors. A dark current of the device can be reduced to 10^-9 A/cm² by introducing a Eu oxide thin-film layer as a carrier blocking layer at the interface between transparent conducting oxide (TCO) and the TiO₂ layer, and the specific detectivity reaches 5.2 × 10¹⁵ jones at 365 nm with -3 V. The performance of our organic-inorganic hybrid photodetector surpasses those of existing ultraviolet photodetectors.

Alkyl chain elongation and acyl group effects in a series of Eu/Tb complexes with hexadentate π-electronic skeletons and their enhanced luminescence in solutions

Enhanced luminescence and structural aspects of bpy-based Eu complexes with long alkyl chains and acyl groups were elucidated in solutions.

Solar-Pumping Upconversion of Interfacial Coordination Nanoparticles

An interfacial coordination nanoparticle successfully exhibited an upconversion blue emission excited by very low-power light irradiation, such as sunlight. The interfacial complex was composed of Yb ions and indigo dye, which formed a nano-ordered thin shell layer on a Tm₂O₃ nanoparticle. At the surface of the Tm₂O₃ particle, the indigo dye can be excited by non-laser excitation at 640 nm, following the intramolecular energy transfer from the indigo dye to the Yb ions. Additionally, the excitation energy of the Yb ion was upconverted to the blue emission of the Tm ion at 475 nm. This upconversion blue emission was achieved by excitation with a CW Xe lamp at an excitation power of 0.14 mW/cm², which is significantly lower than the solar irradiation power of 1.4 mW/cm² at 640 ± 5 nm.

Water-soluble lanthanide complexes with a helical ligand modified for strong luminescence in a wide pH region

Luminescent helical lanthanide complexes with hydrophilicity were examined for stability and reversibility in a pH region between 1.9 and 11.9.

Serum Wisteria floribunda agglutinin-positive Mac-2-binding protein for patients with chronic hepatitis B and C: a comparative study

We compared Wisteria floribunda agglutinin-positive Mac-2-binding protein (WFA⁺ -M2BP) levels between patients with chronic hepatitis B (n=249) and chronic hepatitis C (n=386) based on the degree of liver fibrosis. We examined WFA⁺ -M2BP levels in patients with F4 (cirrhosis), F3 or more (advanced fibrosis) and F2 or more (significant fibrosis) in the two groups. We further examined the relationship between five fibrosis markers and the degree of fibrosis. The WFA⁺ -M2BP values ranged from 0.25 cut-off index (COI) to 12.9 COI in patients with hepatitis B and 0.34-20.0 COI in patients with hepatitis C (P<.0001). The median WFA⁺ -M2BP values in F4 in the two groups were 2.83 COI in patients with hepatitis B and 5.03 COI in patients with hepatitis C (P=.0046). The median WFA⁺ -M2BP values in F3 or more in the two groups were 1.79 COI in patients with hepatitis B and 3.79 COI in patients with hepatitis C (P<.0001). The median WFA⁺ -M2BP values in F2 or more in the two groups were 1.49 COI in the hepatitis B cohort and 3.19 COI in the hepatitis C group (P<.0001). Among five liver fibrosis markers, WFA⁺ -M2BP had the highest correlation coefficient (r_s =.629) in terms of correlation with the degree of fibrosis in the patients with hepatitis C and had the second highest r_s value (.415) in the hepatitis B group. Although WFA⁺ -M2BP could be a useful indicator of liver fibrosis, WFA⁺ -M2BP levels in the two groups significantly differed even in the same degree of fibrosis. Individual cut-off values in each aetiology for the degree of fibrosis should be determined.