Advances in Multichromophoric Metal-Free FRET Macrocycles and 2D Metallacycles

This review highlights the recent advances in the development of multichromophoric, metal-free covalent macrocycles and 2D metallacycles exhibiting Förster resonance energy transfer (FRET) that imparts emergent functions to these structures. The design strategies and synthetic methodologies for multichromophoric macrocycles and their structural diversities have been discussed. A covalent synthetic approach in macrocycle design ensures rigidity and precise chromophoric arrangement while a metal coordination driven self-assembly strategy provides facile access to dynamic structures of 2D metallacycles with tunable (opto)electronic properties. Despite synthetic challenges, macrocyclic architecture offer structural rigidity and minimized excitation traps compared to linear counterparts. This review highlights the key synthetic strategies for metal-free covalent macrocycles, including condensation, templated cyclization, Prato's reaction, and copper-catalyzed azide/alkyne cycloaddition (CuAAC), alongside noncovalent approaches. The discrete nature, size and shape, and photophysical properties of these multichromophoric FRET macrocycles have been leveraged for various applications such as biomedicine, sensing, in vivo imaging, and photocatalysis and their future applications for host-guest chemistry, nanoreactors for photocatalysis, and optoelectronics are discussed.