Theoretical study of lanthanide‐based in vivo luminescent probes for detecting hydrogen peroxide

The 4f‐4f emissions from lanthanide trication (Ln3+) complexes are widely used in bioimaging probes. The emission intensity from Ln3+ depends on the surroundings, and thus, the design of appropriate photo‐antenna ligands is indispensable. In this study, we focus on two probes for detecting hydrogen peroxide, for which emission intensities from Tb3+ are enhanced chemo‐selectively by the H2O2‐mediated oxidation of ligands. To understand the mechanism, the Gibbs free energy profiles of the ground and excited states related to emission and quenching are computed by combining our approximation—called the energy shift method—and density functional theory. The different emission intensities are mainly attributed to different activation barriers for excitation energy transfer from the ligand‐centered triplet (T1) to the Tb3+‐centered excited state. Additionally, quenching from T1 to the ground state via intersystem crossing was inhibited by intramolecular hydrogen bonds only in the highly emissive Tb3+ complexes. © 2018 Wiley Periodicals, Inc. The mechanism of Tb3+‐based in vivo luminescent probes, whose emission intensities are enhanced by the addition of hydrogen peroxide, are examined using the authors' approximation and density functional theory. The reason for different emission intensities is explained by the different activation barriers for excitation energy transfer from ligand‐centered triplet state to Tb3+‐centered excited states.