The First Inert and Photostable Encapsulated Lanthanide(III) Complexes Based on Dendritic 9,10‐Diphenylanthracene Ligands: Synthesis, Strong Near‐Infrared Emission Enhancement, and Photophysical Studies

Abstract

A series of inert and photostable encapsulated lanthanide(III) complexes—based on dendritic anthracene ligands—is shown for the first time to exhibit strong near‐IR emission bands via efficient energy transfer from the excited states of the peripheral antenna to the Ln3+ ions (Er3+, Yb3+, and Nd3+). A significant decrease in the fluorescence of the anthracene ligand is accompanied by a strong increase in the near‐IR emission of the Ln3+ ions. The near‐IR emission intensities of Ln3+ ions in the encapsulated Ln3+–dendrimer complexes are dramatically enhanced on increasing the generation number (n) of dendrons, owing to site‐isolation and light‐harvesting effects. Furthermore, a first attempt is made to distinguish between the site‐isolation and light‐harvesting effects in the present complexes. Photophysical studies indicate the sensitization of Ln3+ luminescence by energy transfer through the excited singlet state of the anthracene ligands, and the energy‐transfer efficiency between the dendritic anthracene ligands and the Ln3+ ion is evaluated to be in the range of 90 to 97 %. Their energy‐transfer efficiency is in good agreement with the result that the biexponential decays contain a radiative decay of anthracene units (< ca. 10 %) and an energy‐transfer component (> ca. 90 %) from the excited state of anthracene ligands to the Ln3+ ions. Time‐resolved luminescence spectra show monoexponential decays with a lifetime of 2 μs for the Er3+ ion 11 μs for the Yb3+ ion and 0.7 μs for the Nd3+ ion in thin films, and calculated intrinsic quantum yields of the Ln3+ ions are in the range of ca. 0.025 to 0.55 %.

Synthesis and Judd–Ofelt analysis of a sol–gel material doped with a Ln2(Benzoate)6(Phen)2 (Ln=Er/Yb) complex

“…In this region around 980 nm, the Yb 3+ has a larger absorption, and therefore, the spectrum shows a strong broad band at 980 nm. Table 1 The main absorption bands of FTIR spectrum for Er 1.4 Yb 0.6 (Benzoate) 6 …”

“…In these compounds, the organic ligands act as photosensitizers or antenna chromophores, efficiently absorbing and transferring the energy of light to excite the lanthanide (Ln 3+ ) ions via an energy-transfer process [5,6]. Among the Ln 3+ ions, Er 3+ is one of the most popular Ln 3+ ions for the characteristic emission around 1550 nm, which is the wavelength currently used in telecommunications.…”

Rare-earth (Eu3+, Tb3+) hybrids through amide bridge: Chemically bonded self-assembly and photophysical properties

“…In those compounds, the emission of Eu 3+ or Tb 3+ complexes usually results from the so-called ''antenna effect", which is defined as a light conversion process via an energy absorption, energy-transfer and emission sequence. In such a process, the organic ligands act as photosensitizers or antenna chromophores to absorb and transfer the energy of light to excite the lanthanide ions via an energy-transfer process [6,7]. Due to the versatility in organic synthesis, the luminescent properties of lanthanide complexes can be custom-tailored depending on the desired application.…”

Dendritic Architectures for Design of Photo– and Spin–Functional Nanomaterials

“…Therefore, mixing the gel of 84 with 1-octanol, which is a scavenger of the hydrogen bonding, results in spin transition and gel-to-sol phase transition simultaneously. In fact, on addition of different amounts of 1-octanol to the gel, the spin-transition temperature can be changed over a wide range from 65 to 20 C. The spin-crossover gels are characterized by their narrower temperature range for the spin transition than the solid samples, synchronous to the sol-gel phase transition, and their quick response to temperature changes both on heating and cooling. Since gels are generally more sensitive than solids to external perturbations, the spin-crossover gels may have a large potential in, e.g., sensory applications.…”

“…To clarify siteisolation effect of dendritic wedges, Kim and coworkers have employed poly(benzyl ether) dendrons bearing a focal anthracene carboxylic acid unit to coordinate with Ln 3þ in the presence of terpyridine as a coligand. 20 A film of Er 3þ complex 11, upon excitation of the anthracene unit at 357 nm, emits at 1530 nm, whose intensity is 4.8 times stronger than that upon excitation of poly(benzyl ether) dendron at 290 nm. As the generation number of the dendrons increases from 0 to 3, the emission intensity is enhanced by more than 100 folds upon excitation at the anthracene unit.…”