Design and synthesis of near-infrared emissive lanthanide complexes based on macrocyclic ligands

This review firstly summarizes our recent work on the preparation and photophysical properties of cationic or neutral lanthanide(III) monoporphyrinate complexes, as well as some bridging dinuclear complexes, in which the porphyrinate anion can sensitize the NIR emission of Nd^III, Yb ^III and Er^III ions by serving as an antenna that absorbs visible light and transfers the energy to the excited state of the lanthanide(III) ion, followed by relaxation through the NIR emission. Next, several d-f heterobimetallic diporphyrin complexes, in which a transition metal (M = Zn, Pd, and Pt) porphyrinate moiety serves as a donor by transferring its energy to the Yb³⁺ ion and enhances the NIR emission, are described. In addition, the synthesis and photophysical properties of some Gd^III porphyrinate complexes and monophthalocyaninato lanthanide complexes are also described in this contribution. Apart from the above compounds, we also discuss the construction of multidecker multimetallic lanthanide Schiff base assemblies, which demonstrate that these varieties of salen-type Schiff base ligands can stabilize Ln^III centers and provide the antenna for lanthanide luminescence. By taking advantage of the absorption and emission properties of transition-metal Schiff base complexes, multinuclear and polynuclear Zn ^II-Ln^III Schiff base complexes have also been constructed with improved luminescence properties. Various synthetic strategies have been described for encapsulating lanthanide ions into molecular edifices and making use of macrocyclic (viz. porphyrins, phthalocyanines and their derivatives) or acyclic ligands as well as d-transition-metal complexes (i.e. Schiff base and their transition-metal complexes) to sensitize the near-infrared-emitting trivalent lanthanide ions.