Isoquinoline-based Eu(iii) luminescent probes for citrate sensing in complex matrix

Influence of Hydroxycoumarin Substituents on the Photophysical Properties of Chiroptical Tb(III) and Eu(III) Complexes

In this article, the synthesis, density functional theory (DFT) structural characterization, and spectroscopic investigation of chiral and heteroleptic Tb(III) and Eu(III) complexes are presented. These molecules are characterized by two different ligands: the enantiopure N,N'-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane-N,N'-diacetic acid (H2bpcd) and a hydroxycoumarin-based ligand bearing different substituents in C(3) position (i.e., acetyl group in Coum, ethyl ester in CoumA, secondary and tertiary amides in CoumB and CoumC, respectively). The coumarin ligands exhibited different luminescence sensitization efficiency toward Tb(III) and Eu(III) ions in the related complexes of chemical formula [Ln(bpcd)(Coum)], [Ln(bpcd)(CoumA)], [Ln(bpcd)(CoumB)], [Ln(bpcd)(CoumC)]. Through theoretical calculations of intramolecular energy transfer (IET) processes (ligand-to-metal) in Eu(III) and Tb(III) complexes, along with quantum yield calculations, we provide a reasonable explanation for the observed differences in their luminescence properties. The nature of the coumarin ligand also affects the chiroptical properties of the Tb(III) complexes [i.e., circularly polarized luminescence (CPL) and electronic circular dichroism (ECD)].

Synthesis of 1-Aminoisoquinolines and Their Application in a Host-Guest Doped Strategy To Construct Ultralong Room-Temperature Phosphorescence Materials for Bioimaging

Organic ultralong room-temperature phosphorescence (RTP) materials have attracted great attention for their wide applications in optoelectronic devices and bioimaging. However, the development of these materials remains a challenging task, partially due to the lack of rational molecular design strategies and unclear luminescence mechanisms. Herein, we present a method for facile access to structurally diverse substituted 1-aminoisoquinoline derivatives through a copper-catalyzed one-pot three-component coupling reaction that provides a promising approach to rapidly assemble a library of 1-aminoisoquinolines for exploring the regularity of the host-guest doped system. A series of host-guest RTP materials with wide-ranging lifetimes from 4.4 to 299.3 ms were constructed by doping various substituted isoquinolines derivatives into benzophenone (BP). Furthermore, 4 r/BP nanoparticles could be used for in-vivo imaging with a signal-to-noise ratio value as high as 32, revealing the potential of the isoquinoline framework for the construction of high-performance RTP materials.

Dynamics of the Energy Transfer Process in Eu(III) Complexes Containing Polydentate Ligands Based on Pyridine, Quinoline, and Isoquinoline as Chromophoric Antennae

In this work, we investigated from a theoretical point of view the dynamics of the energy transfer process from the ligand to Eu(III) ion for 12 isomeric species originating from six different complexes differing by nature of the ligand and the total charge. The cationic complexes present the general formula [Eu(L)(H₂O)₂]⁺ (where L = bpcd^2– = N,N′-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane N,N′-diacetate; bQcd^2– = N,N′-bis(2-quinolinmethyl)-trans-1,2-diaminocyclohexane N,N′-diacetate; and bisoQcd^2– = N,N′-bis(2-isoquinolinmethyl)-trans-1,2-diaminocyclohexane N,N′-diacetate), while the neutral complexes present the Eu(L)(H₂O)₂ formula (where L = PyC3A^3– = N-picolyl-N,N′,N′-trans-1,2-cyclohexylenediaminetriacetate; QC3A^3– = N-quinolyl-N,N′,N′-trans-1,2-cyclohexylenediaminetriacetate; and isoQC3A^3– = N-isoquinolyl-N,N′,N′-trans-1,2-cyclohexylenediaminetriacetate). Time-dependent density functional theory (TD-DFT) calculations provided the energy of the ligand excited donor states, distances between donor and acceptor orbitals involved in the energy transfer mechanism (R_L), spin-orbit coupling matrix elements, and excited-state reorganization energies. The intramolecular energy transfer (IET) rates for both singlet-triplet intersystem crossing and ligand-to-metal (and vice versa) involving a multitude of ligand and Eu(III) levels and the theoretical overall quantum yields (ϕ_ovl) were calculated (the latter for the first time without the introduction of experimental parameters). This was achieved using a blend of DFT, Judd–Ofelt theory, IET theory, and rate equation modeling. Thanks to this study, for each isomeric species, the most efficient IET process feeding the Eu(III) excited state, its related physical mechanism (exchange interaction), and the reasons for a better or worse overall energy transfer efficiency (η_sens) in the different complexes were determined. The spectroscopically measured ϕ_ovl values are in good agreement with the ones obtained theoretically in this work.

Photophysical properties of 12 Eu(III) complexes with pyridine, quinoline, and isoquinoline ligands in aqueous solutions were elucidated and predicted through a theoretical protocol using a blend of DFT, Judd−Ofelt theory, intramolecular energy transfer theory, and coupled rate equation modeling calculations. The theoretical procedure is general and can be extended to any lanthanide-based complexes.