Preparation and Photoluminescence Properties of Polymer–Rare-Earth Complexes Composed of Bidentate Schiff-Base-Ligand-Functionalized Polysulfone and Eu(III) Ion

Abstract

A bidentate Schiff base (SB) ligand was synthesized and bonded on the side chains of polysulfone (PSF) via several polymer reactions by molecular design, and the bidentate Schiff base ligand-functionalized PSF, PSF-SB, was gained. On this basis, a new type of polymer-rare earth complexes, binary complex PSF-(SB) 3 -Eu(Ⅲ) and ternary complex PSF-(SB) 3 -Eu(Ⅲ)-(Phen) 1 , was prepared via the coordination reactions between PSF-SB as macromolecular ligand and 1,10-phenanthroline (Phen) as the second small-molecule ligand and Eu(Ⅲ) ion, respectively. The functional polymer PSF-SB was fully characterized by FTIR, 1 H-NMR and chemical analysis method, and the complexes were also fully characterized by FTIR and UV absorption spectroscopy. The fluorescence emission characteristics and luminescent mechanism of the complexes were investigated in depth. The experimental results show that the macromolecular ligand PSF-SB itself emits strong fluorescence centered at 415 nm. However, after coordinating to Eu(Ⅲ) ion, the fluorescence emission of PSF-SB itself weakens remarkably, and it should be attributed to the intramolecular energy transfer. Both the binary and ternary complexes exhibit the strong characteristic fluorescence emission of Eu(Ⅲ) ion. This fact demonstrates that the bidentate Schiff base ligand SB bonded on the side chains of PSF can effectively produce the intramolecular energy transfer, namely it can strongly sensitize the fluorescence emission of Eu(Ⅲ) ion, indicating that the triplet state energy of the bonded ligand SB is well matched with the resonant level energy of Eu(III) ion. The fluorescence emission intensity of the ternary complex PSF-(SB) 3 -Eu(Ⅲ)-(Phen) 1 is stronger than that of the binary complex PSF-(SB) 3 -Eu(Ⅲ), and it associates with the synergism coordination of the second ligand Phen with the bond ligand SB as well as its effect of substituting the coordinated water molecules around Eu(Ⅲ) ion. structure a larger conjugated aromatic ring is contained, onto the side chain of PSF, and a bidentate Schiff base ligand-functionalized polysulfone, PSF-SB, was successfully prepared through 3-step macromolecular reactions. Finally, the binary and ternary polymer-rare earth (Eu(Ⅲ) and Tb(Ⅲ)) complexes were obtained, and their photoluminescence properties and luminescent mechanism were researched. The study result showed that the bidentate Schiff base ligand bonded to the side chains of PSF, SB, can strongly sensitize the fluorescence emission of Eu(Ⅲ) ion because of the better energy level matching. To our knowledge, the luminescent bidentate Schiff base-type polymer-rare earth complexes have not been reported in the literature. The study result in this work is significant in developing photoluminescence polymer-rare earth complex materials.

Synthesis and luminescence properties of polymer–rare earth complexes containing salicylaldehyde‐type bidentate Schiff base ligand

“…Recently, we synchronously synthesized and bonded a bidentate Schiff base ligand with the type of benzaldehyde–aminopyridine on the side chain of PSF, and obtained a bidentate Schiff base ligand‐functionalized PSF. Finally, via coordination reaction, polymer–Eu(III) complexes with red emission were obtained, and a Schiff base‐type polymer–RE complex was reported for the first time. This is a significant breakthrough in luminescent polymer–RE complex materials.…”

“…Using the procedure described in Gao et al, PSF was first chloromethylated with BCMB. PSF was dissolved in dichloromethane, followed by addition of SnCl 4 as a Lewis acid catalyst; the chloromethylation reagent BCMB was then slowly added dropwise.…”

“…The total volume of the supernatant was 200 ml, made up of 50 ml DMAC and 150 ml ethanol. A known volume of supernatant was taken to determine conversion of the chloromethyl group of CMPSF or the bonding degree of HSA on the side chain of PSF using ultraviolet (UV) spectrophotometry at 279 nm, as described in Gao et al The obtained polymer product was washed with ethanol and distilled water alternately, and was dried under vacuum, resulting in the modified polysulfone, PSF–SA, on whose side chain salicylaldehyde as a group was bonded. The determination result indicated that for PSF–SA, the chloromethyl group conversion of CMPSF was 90%.…”

“…This is a significant breakthrough in luminescent polymer–RE complex materials. However, the bidentate Schiff base ligand‐functionalized PSF in Gao et al coordinated only to the Eu(III) ion to form polymer–RE complexes displaying red luminescence, whereas polymer–Tb(III) complexes emitting green fluorescence could not obtained. It is obvious that the chemical structures of the macromolecular or bond ligands greatly affect the luminescent properties of the complexes.…”

“…The mechanism of their luminescence and the relationship between their structures and photoluminescence properties were investigated. Compared with Gao et al, this study is a new development, and both red and green luminescent complexes are obtained at the same time. Therefore, this work further expands and enriches luminescent polymer–RE complexes containing Schiff base type ligands via a new molecular design.…”