Controlling Lanthanide Exchange in Triple-Stranded Helicates: A Way to Optimize Molecular Light-Upconversion.

The kinetic lability of hexadentate gallium-based tripods is sufficient to ensure thermodynamic self-assembly of luminescent heterodimetallic [GaLn(L3)3 ](6+) helicates on the hour time scale, where Ln is a trivalent 4f-block cation. The inertness is, however, large enough for preserving the triple-helical structure when [GaLn(L3)3 ](6+) is exposed to lanthanide exchange. The connection of a second gallium-based tripod further slows down the exchange processes to such an extent that spectroscopically active [CrErCr(L4)3 ](9+) can be diluted into closed-shell [GaYGa(L4)3 ](9+) matrices without metal scrambling. This feature is exploited for pushing molecular-based energy-transfer upconversion (ETU) at room temperature.