General method

¹H-NMR spectra were recorded in CDCl₃ on a JEOL ECS-400 (400 MHz) spectrometer; tetramethylsilane was used as the internal reference. Electron ionization (EI) and electrospray ionization (ESI) mass spectrometry were performed using JEOL JMS-T100 GCv and JEOL JMS-T100 LP instruments, respectively. Elemental analyses were performed using MICRO CORDER JM10. UV-vis absorption spectra for ligand 1 and Eu(III) complex 2 were measured using a JASCO V-670 spectrophotometer. Emission spectrum, excitation spectrum, and emission lifetime for Eu(III) complex 2 were measured using a Horiba FluoroLog®3 spectrofluorometer. Emission spectrum and lifetime for Gd(III) complex 5 were measured using a FP-6300 spectrofluorometer with a nitrogen bath cryostat (Oxford Instruments, Optistat DN) and a temperature controller (Oxford Instruments ITC-502S). Emission spectrum for the ligand 1 was measured using a FP-6300 spectrofluorometer with a nitrogen bath cryostat (Oxford Instruments, Optistat DN) and a temperature controller (Oxford Instruments ITC-502S). Emission quantum yield for Eu(III) complex 2 was measured using a FP-6300 spectrofluorometer with an integration sphere (ILF-533).