Chirality and Chiroptics of Lanthanide Molecular and Supramolecular Assemblies

Chiroptical probes based on circular dichroism (CD) and circularly polarized luminescence (CPL) are crucial for understanding chirality in nature. Lanthanide chiroptical complexes are considered as promising candidates for the more sensitive CPL because of their unique optical properties, such as the magnetic dipole-allowed but electric-dipole-forbidden f-f transitions, large pseudo-Stokes shift, and long luminescence lifetime. However, due to the non-directional nature of lanthanide ions which allows variable coordination numbers, the design of their chiral complexes, especially at the supramolecular level, remains a challenge. Recent developments demonstrate the assemblies of chiroptical helices, cages, wheels, knots, and frameworks, which opens up future potential for applications such as in sensing and chiral guest recognition. This review provides the basics of coordination chemistry and photophysics of lanthanide ions, introduces chiroptical characterization, and summarizes the progress on the development of chiroptical lanthanide molecular and supramolecular systems. Perspectives on future development and applications are also discussed. Chirality governs the fundamental properties of life, from how our left and right hands complement each other to the drastically different efficacy of two drug enantiomers. Light can be used to characterize chirality by observing its circular polarization when passed through a chiral environment. In this work, the basics of chiroptical properties and the progression of developing lanthanide compounds for chiroptical spectroscopy are reviewed, a wide spectrum of chelate systems and strategies to construct molecular and supramolecular assemblies are summarized, and the relationship between the chiral environment and chiroptical properties is elucidated; moreover, applications based on specific chiral interactions are also reported. The authors are convinced that chiral lanthanide assemblies could help explore new, previously unappreciated avenues in applications that will improve the health and well-being of mankind, benefiting from increased specificity and selectivity. Chirality is essential in life, and light is employed to understand it. The unique photophysical and magnetic properties of lanthanides allow a sizable signal of circularly polarized luminescence. Herein, we discuss the perspective of this field and summarize the coordination chemistry, chiroptical properties, and applications of lanthanide molecular and supramolecular assemblies.