Turning 3D Covalent Organic Frameworks into Luminescent Ratiometric Temperature Sensors

In this study, we report hybrid crystalline lanthanide-containing3D covalent organic framework (Ln@3D COF) materials that are suitablefor temperature sensing applications. Different routes to obtain thesehybrid materials were tested and compared for material quality andthermometric properties. In the first approach, a bipyridine-containing3D COF (Bipy COF) was grafted with a range of visible emitting lanthanide(Eu3+, Tb3+, Dy3+, and Eu3+/Tb3+) & beta;-diketonate complexes. In the second approach,a novel nanocomposite material was prepared by embedding NaYF4:Er,Yb nanoparticles on the surface of a nonfunctionalized3D COF (COF-300). To the best of our knowledge, the luminescent materialsdeveloped here are the first 3D COFs to be tested as ratiometric temperaturesensors. In fact, for the Bipy COF, two different types of thermometerswere tested (the Eu3+/Tb3+ system and a rareDy(3+) system), with both showing excellent temperature sensingproperties. The reported NaYF4:Er,Yb/COF-300 nanocompositematerial combines upconverting nanoparticles with 3D COFs, similarto previously reported metal organic framework (MOF) nanocompositematerials; however, this type of hybrid material has not yet beenexplored for COFs. As such, our findings open a new pathway towardpotential multifunctional materials that can combine thermometry withother modalities, such as catalysis or drug delivery, in just onenanocomposite material.