Luminescent Compounds, Complexes and Their Uses

A complex comprising:

• a multidentate ligand that is coordinated to a lanthanide ion, wherein
• the lanthanide is selected from europium and terbium, and
• the multidentate ligand has (i) at least one optionally substituted phthalimide group coordinated to the lanthanide ion or (ii) at least one optionally substituted phthalamate group coordinated to the lanthanide ion.

A method of changing the fluorescent properties of a complex, the method comprising:

• providing a first complex comprising a multidentate ligand that is coordinated to a lanthanide ion,
• wherein the lanthanide is selected from europium and terbium and the multidentate ligand has at least one optionally substituted phthalimide group coordinated to the lanthanide ion,
• contacting the complex with an aqueous liquid medium under appropriate conditions, such that at least one phthalimide group is hydrolyzed to a phthalamate group, to form a second complex.

Use of a complex for detecting a change in pH, wherein the complex comprises a multidentate ligand that is coordinated to a lanthanide ion, wherein the lanthanide is selected from europium and terbium and the multidentate ligand has (i) at least one optionally substituted phthalimide group coordinated to the lanthanide ion or (ii) at least one optionally substituted phthalamate group coordinated to the lanthanide ion.