Predicting Efficient Antenna Ligands for Tb(III) Emission

Abstract

ABSTRACT:A series of highly luminescent Tb(III) complexes of para-substituted 2-hydroxyisophthalamide ligands (5LI-IAM-X) has been prepared (X = H, CH 3 , (C=O)NHCH 3 , SO 3 -, NO 2 , OCH 3 , F, Cl, Br) to probe the effect of substituting the isophthalamide ring on ligand and Tb(III) emission in order to establish a method for predicting the effects of chromophore modification on Tb(III) luminescence. The energies of the ligand singlet and triplet excited states are found to increase linearly with the -withdrawing ability of the substituent. The experimental results are supported by 2 time-dependent density functional theory (TD-DFT) calculations performed on model systems, which predict ligand singlet and triplet energies within ~5% of the experimental values. The quantum yield () values of the Tb(III) complex increases with the triplet energy of the ligand, which is in part due to the decreased non-radiative deactivation caused by thermal repopulation of the triplet. Together, the experimental and theoretical results serve as a predictive tool that can be used to guide the synthesis of ligands used to sensitize lanthanide luminescence.

Structures, luminescence and vibrational spectroscopy of europium and terbium nitro- and dinitro-substituted benzoates. Nitro groups as quenchers of Ln3+ luminescence

“…The lowest triplet state T n * can decay non-radiatively to the ground state of nitrobenzoate analogously to that studied in Refs. [9,11] for ligands containing the nitro group. So, the S n * state should be regarded as a quenching one.…”

“…So, the S n * state should be regarded as a quenching one. Both S n * and T n * states in the nitrobenzoates under investigation should involve an excitation of the electron density from the n-state of NO 2 oxygen lone pairs to the * system of ligand, in analogy to the nature of these states in the nitro-phenanthroline and nitro-bipyridine ligands of d 6 metal complexes [11] and in the terbium nitro-substituted 2-hydroxyisophthalamide [9].…”

“…Hypothetically, this effect is caused by participation of n-* transition of nitro group with admixing an intraligand charge transfer (ILCT) in dissipation of the excitation energy and by a low energy of the ligand lowest triplet state [2,4]. ILCT contributions to singlet-singlet and singlet-triplet transitions in the terbium nitro-substituted 2-hydroxyisophthalamide were demonstrated by TD-DFT calculations [9]. The authors supposed that the triplet state mentioned may be located too low or the ligand emission lifetime may be short for efficient energy transfer to Tb 3+ ion.…”

Lanthanide complexes as chiral probes exploiting circularly polarized luminescence

“…Further vibrational relaxation then occurs so only the lowest vibrational level of the S 1 37 Meanwhile, Φ Ln is the intrinsic quantum yield of the lanthanide ion, which was defined and discussed in Section 1.3.1.…”

Fluorescent polymeric aggregates induced by Eu3+ ions and their surface morphologies

“…However, the absorbance of ultraviolet radiation by rare earth ions is very weak, thereby establishing an upper limit on the potential to enhance fluorescence without chemical modification of the corresponding macromolecule-lanthanide complexes. This problem is addressed by introducing ''antenna ligands'' within the polymer chain [7][8][9][10][11]. Hence, one incorporates selected ligands that form complexes with lanthanide cations, such as UV-light-absorbing Si-O and pyridine [12][13][14].…”