Efficient Donor for Terbium Luminescence Based on Polymer Ligand Containing Quinolinone Fluorophore

Abstract

AbstractSummary: Polymer ligand containing a quinolinone fluorophore and carboxyl binding sites (III) was synthesized by the reaction of parent poly[styrene‐alt‐(maleic anhydride)] with 7‐amino‐4‐methylquinolin‐2(1H)‐one (I) and methanol. The ligand‐to‐metal resonance energy transfer and ligand binding properties of Tb(III)‐III complexes were investigated by steady‐state and time‐resolved luminescence spectroscopy in methanol or deuterated methanol and compared with those of the low‐molecular‐weight model compound, N‐[4‐methyl‐2‐oxo‐1,2‐dihydroquinolin‐7‐yl]succinamic acid (II). The long‐lived emission intensity of Tb3+ at 490, 545, 585, and 620 nm corresponding to the 5D4 → 7F6, 5D4 → 7F5, 5D4 → 7F4, and 5D4 → 7F3 transitions, respectively, was strongly increased by the addition of III (as much as 10 000 times) and decreased in the order of Tb(III)‐III ≫ Tb(III)‐II > Tb(III)‐I > Tb(III). The efficiency of energy transfer (E) was evaluated from emission intensity of the donor (III) in the presence or absence of the acceptor (Tb3+) as E = 0.71–0.94, depending on the acceptor concentration and ligand neutralization. The experimental luminescence‐decay curves were double‐exponential (τ1, τ2) with a predominating longer component (rel B1 = 85%) for Tb(III)‐III and single‐exponential (τ) for Tb(III)‐II. One or three methanol molecules were coordinated to Tb3+ in Tb(III)‐III with or without neutralization of III, respectively, whereas approximately 6.5 methanol molecules were coordinated to Tb3+ in Tb(III)‐II. Terbium ion coordinates with 7–8 molecules of methanol in methanolic solution.Schematic energy‐level diagram for fluorescence resonance energy transfer in a Tb(III)‐ligand complex.magnified imageSchematic energy‐level diagram for fluorescence resonance energy transfer in a Tb(III)‐ligand complex.