Highly Luminescent Europium-Based Heteroleptic Coordination Polymers with Phenantroline and Glutarate Ligands

Abstract

Isostructural lanthanide-based coordination polymers with general chemical formula [Ln­(phen)­(glu)­(NO3)]∞ with Ln = La–Tm (except Ce and Pm) have been synthesized by hydrothermal methods (H2glu stands for glutaric acid and phen stands for 1,10-phenantroline). They crystallize in the monoclinic system with the P21/c (no. 14) space group. The crystal structure has been solved on the basis of the La derivative. It can be described as the superimposition of molecular chains of dimeric La­(phen)­(NO3)-La­(phen)­(NO3) units bridged by glutarate ligands. Luminescent properties have been explored and show that the Eu derivative exhibits the highest luminance observed for Eu-based coordination polymers (85 to 105 cd·m–2). Effects of the dilution of the Eu3 + and Tb3 + luminescent ions by Gd3 + optically inactive ions are unexpected and to the best of our knowledge unprecedented. This could be related to the different intermetallic energy-transfer mechanisms in competition and to the nonisotropic distribution of the lanthanide ions in these molecular alloys. The investigation of molecular alloys with general chemical formula [Eu1–x Tb x (phen)­(glu)­(NO3)]∞ with 0 ≤ x ≤ 1 highlights a very sizable and constant Eu3 + luminescence whatever the x value, which further confirms the existence of very strong intermetallic energy transfers in this family of compounds. It is also noticeable that some coordination polymers based on weakly emissive lanthanide ions exhibit very well defined emission spectra.

Enhancement of the Luminescence Properties of Eu (III) Containing Paramagnetic Saponite Clays

“…The emission spectra of Phen-GdEuSAP samples, collected under irradiation at both 290 (λexc of Phen) and 395 nm (λexc of Eu 3+ ) (Figure 3), showed that upon direct excitation of the antenna group there is a marked increase in the intensity of the hypersensitive 5 D0-7 F2 transition at 615 nm of Eu 3+ compared to the direct excitation of the lanthanide, thus confirming the interaction of Phen molecules with Eu 3+ sites and the occurrence of the ligand-to-metal energy transfer phenomenon [36,37,50]. The emission spectra of both hybrid materials excited at 290 nm (λmax of Phen) shown in Figure 3 also show a broad emission band centered at 415 nm associated with the residual T1 → S0 ( 3 π* → 1 π) electronic transition of Phen [46][47][48][49]54] (Figure S5B).…”

“…The excitation spectrum of the Phen-GdEuSAP_1 sample collected at 615 nm (Figure S4) shows the characteristic narrow peaks of the intra-4f 6 electronic transitions of Eu 3+ ( 5 D 0 -7 F J , J = 0-4; λ max = 395 nm, 7 F 0 -5 L 6 ) [52] and Gd 3+ ( 8 S 7/2 -6 I J ; λ max = 272 nm, 8 S 7/2 -6 P J ) [53] together with the S 0 → S 1 ( 1 π → 1 π*) electronic transition of the Phen, located at 290 nm [46][47][48][49]54] (Figure S5A).…”

“…The parameters were derived from the time-resolved fluorescence spectroscopy analyses at solid state of the experimental lifetimes (τ D ) of the Donor system (Phen-SAP clays) and those (τ DA ) of the Donor-Acceptor (Phen-GdEuSAP clays), collecting the decay curves of the S 0 excited state of Phen at 415 nm [46][47][48][49]54] upon excitation at 295 nm (Figure S7A,B for Phen-GdEuSAP samples and Figure S8A,B for Phen-SAP samples). The curves were well fitted with a bi-exponential function, obtaining average τ values for each one.…”

“…Pristine Na + -exchanged saponite (Na-SAP) intercalated with Phen molecules was also prepared as the reference material (Phen-SAP). The 1,10-phenanthroline molecule was chosen because it is a common photo-enhancer for Eu 3+ -based compounds used in literature [46][47][48][49], since it is able to interact easily with Eu 3+ and transfer energy to its nearby emitting sites through a ligand-to-metal energy transfer process (antenna effect) [36,37,50]. This non-radiative mechanism is based on a phononmediated coulombic (dipolar-dipolar) interaction between the Phen (donor group) and the Eu 3+ (acceptor group), which can effectively enhance the photoluminescence performance of europium [46][47][48][49].…”

Two luminescent film sensors constructed from new lanthanide coordination polymers for ratiometric detection of Zn2+ and NH3 in water and their white emission properties

“…According to previous reports, the S 1 of the ligand was calculated to be 30 120 cm −1 (332 nm) by referring to the absorbance edges of the UV–Vis spectra. 34 As depicted in Fig. 3b, the phosphorescence spectrum of GdL at 77 K showed broad bands ranging from 380 to 600 nm with the maximum peak appearing at 420 nm (23 809 cm −1 ).…”