Luminescent Nanothermometers Obtained by Post‐Synthetic Modification of Metal‐Organic Framework MIL‐68

Metal‐organic frameworks (MOFs) bearing lanthanide ions are excellent platforms for designing luminescent thermometers. However, so far, post‐synthetic modification of MOFs linkers has not been explored as a route to produce such thermometers, despite its potential to design the lanthanide coordination sphere and, thus, tune the emission properties of the material. Here, nanocrystals of MIL‐68‐NH 2 were post‐synthetically modified via a cross‐linking reaction with 1,4‐Bis{4‐[( E )‐3‐( N , N ‐dimethylamino)prop‐2‐enoyl]phenoxy}butane (HL), followed by coordination to Eu 3+ and Tb 3+ ions. The luminescence properties of the material were assessed. Tb 90 Eu 10 ‐MIL‐68‐HL was found to be an excellent cryogenic (< 100 K) ratiometric luminescent nanothermometer exhibiting a maximum relative sensitivity of 9.4 % K –1 at 12 K.