Photosensized controlling benzyl methacrylate-based matrix enhanced Eu(3+) narrow-band emission for fluorescence applications

Abstract

This study synthesized a europium (Eu(3+)) complex Eu(DBM)(3)Cl-MIP (DBM = dibenzoyl methane; Cl-MIP = 2-(2-chlorophenyl)-1-methyl-1H-imidazo[4,5-f][1,10]phenanthroline) dispersed in a benzyl methacrylate (BMA) monomer and treated with ultraviolet (UV) light for polymerization. Spectral results showed that the europium complex containing an antenna, Cl-MIP, which had higher triplet energy into the Eu(3+) energy level, was an energetically enhanced europium emission. Typical stacking behaviors of π-π interactions between the ligands and the Eu(3+)-ion were analyzed using single crystal X-ray diffraction. Regarding the luminescence performance of this europium composite, the ligand/defect emission was suppressed by dispersion in a poly-BMA (PBMA) matrix. The underlying mechanism of the effective enhancement of the pure Eu(3+) emission was attributed to the combined effects of structural modifications, defect emissions, and carrier charge transfer. Fluorescence spectra were compared to the composite of optimized Eu3+ emission where they were subsequently chelated to four metal ions via carboxylate groups on the BMA unit. The optical enhanced europium composite clearly demonstrated highly efficient optical responses and is, therefore a promising application as an optical detection material.

Keywords: UV-curing; europium complex; fluorescence detection; metal-ion chelating; optical tuning.

Figure 1

(a) Absorption and Photoluminescence (PL) spectra of Cl-MIP and Eu(DBM)₃Cl-MIP; (b) Photoluminescence excitation spectrum of Eu(DBM)₃Cl-MIP (in CH₂Cl₂, 2 × 10⁻⁵ M); (c) Photoluminescence spectrum of Eu(DBM)₃Cl-MIP with the benzyl methacrylate (BMA) matrix at a 1.0 wt% level, after ultraviolet-lamp curing for 360 s.

Figure 1

(a) Absorption and Photoluminescence (PL) spectra of Cl-MIP and Eu(DBM)₃Cl-MIP; (b) Photoluminescence excitation spectrum of Eu(DBM)₃Cl-MIP (in CH₂Cl₂, 2 × 10⁻⁵ M); (c) Photoluminescence spectrum of Eu(DBM)₃Cl-MIP with the benzyl methacrylate (BMA) matrix at a 1.0 wt% level, after ultraviolet-lamp curing for 360 s.

Figure 2

(a) Intensities of the photoluminescence spectra of the europium/PBMA composite with different Eu³⁺ contents; (b) Dependence of the Eu³⁺ emission ratio and Eu³⁺/defect emission ratio of the Eu³⁺ content.

Figure 3

(a) Intensities of the photoluminescence spectra of the europium/PBMA composite with different ultraviolet (UV)-curing time; (b) Dependence of the europium emission ratio and Eu³⁺/defect on the BMA UV-curing time.

Figure 4

Optical transmittance, reflectance (a) and absorbance (b) spectra in the thin-film state. The test samples were bare PBMA (black-line), PRISTINE Eu(DBM)₃Cl-MIP (red-line), and a Eu³⁺/PBMA composite (green-line), with an average thickness of ~22 μm and a scan range of 0.4~2.0 μm.

Figure 5

Phosphorescence spectra of (1) Cl-MIP (green-line); (2) DBM in PBMA (navy-line); (3) EuCl₃.6H20 in PBMA (grey-line); (4) EuCl₃.6 H₂O + DBM in PBMA (red-line); and (5) Eu(DBM)₃Cl-MIP (blue-line), λ_ex = 375 nm.

Figure 6

Carrier transfer process of Eu³⁺/BMA composites with and without emissive defects in Eu³⁺ resonance energy levels. Internal conversion (IC); intersystem crossing process (ISC).

Figure 7

Photoluminescence spectra of the Eu³⁺/PBMA composite and neat Eu(DBM)₃Cl-MIP under identical conditions. Ligand emission signals indicate an amplified scale of ~417 nm, as shown in the inset.

Figure 8

PL signal variations of Fe³⁺, Zn²⁺, Ca²⁺, and Mg²⁺ ions by weight concentration in Eu³⁺/PBMA and ionic contents obtained from those ions as a solution with a 0.0243 g/0.5 g BMA mixture. The fluorescence signals, in situ recording of four metal ions binding to the Eu³⁺/PBMA composite at a scan rate of 240 nm/min and excitation at 360 nm.

Scheme 1

Synthetic illustration of the preparation of the ligand 2-(2-chlorophenyl)-1-methyl-1H-imidazo[4,5-f][1,10] phenanthroline (Cl-MIP), Eu³⁺compound (Eu(DBM)₃Cl-MIP), and Eu³⁺/poly-BMA (PBMA) composite films by conducting a photo-polymerization process. Conditions included: (a) NH₄OAc, phenanthracenedione, glacial HOAc, reflux for 2 h (61%); (b) NaH, CH₃I, DMF at room temperature for 18 h (85%); and (c) 1 N NaOH (aq), EuCl₃.6H₂O, anhydrous EtOH at 50 °C for 5 h, pH~7 (67%); (d) The test sample was covered with PET film, and then exposed to ultraviolet light for 300 s.

Chart 1

(a) Molecular structure of Eu(DBM)₃Cl-MIP, showing the atom-labeling scheme and thermal ellipsoids; (b) π–π interactions of the Eu(DBM)₃Cl-MIP complex. Dashed lines represent π–π interactions.