Developing Luminescent Ratiometric Thermometers Based on a Covalent Organic Framework (COF)

Abstract

Covalent Organic Frameworks (COFs), an emerging class of crystalline porous materials, are proposed as a new type of support for grafting lanthanide ions (Ln³⁺ ) and employing these hybrid materials as ratiometric luminescent thermometers. A TpBpy-COF-prepared from 1,3,5-triformylphloroglucinol (Tp) and 2,2'-bipyridine-5,5'-diamine (Bpy) grafted with Eu/Tb and Dy acetylacetone (acac) complexes can be successfully used as a luminescent thermometer in the 10-360 K (Eu) and 280-440 K (Tb) ranges with good sensing properties (thermal sensitivity up to 1.403 % K^-1 , temperature uncertainty δT<1 K above 110 K). For the Eu/Tb systems, we observe an unusual and rarely reported behavior, that is, no thermal quenching of the Tb³⁺ emission, a result of the absence of ion-to-ligand/host energy back-transfer. The LnCOF materials proposed here could be a new class of materials employed for temperature-sensing applications following up on the well-known luminescent metal-organic framework thermometers.