Ratiometric thermometers based on rhodamine B and fluorescein dye-incorporated (nano) cyclodextrin metal-organic frameworks

Macro- and nanosized core, as well as core-shell, gamma-cyclodextrin metal-organic frameworks (gamma-CD-MOFs) have been designed and used as platforms for the encapsulation of dye molecules to develop the first CD-MOF-based ratiometric optical thermometer materials. A novel dye combination was employed for this purpose, i.e., the duo rhodamine B (RhB) and fluorescein (FL). RhB is highly temperature-sensitive, whereas FL is less temperature-sensitive, and its luminescence emission peak is used as a reference. Promising results in terms of thermometric properties were obtained for a series of dye-encapsulated gamma-CD-MOF materials based on this dye combination, with high relative sensitivities, even up to 5%K-1, for the dye-encapsulated 75%RhB-25%FL nanosized gamma-CD-MOF, among the highest performance values reported so far for luminescent dual thermometers. In our study, we have additionally developed a simple yet effective preparation method for core-shell gamma-CD-MOFs, allowing effective manipulation of the gamma-CD-MOF shell growth. The proposed method allows incorporation of the FL and RhB dyes in the gamma-CD-MOFs in a more controlled manner, enhancing the efficiency of the developed ratiometric (macro) gamma-CD-MOF thermometers