Ratiometric and Colorimetric Optical Thermometers Using Emissive Dimeric and Trimeric {[Au(SCN)2]-}n Moieties Generated in d-f Heterometallic Assemblies

Gold complexes can generate excimers ([Au-2]->[Au-2]*) and exciplexes ([Au-3]->[Au-3]*) with light excitation. Four Gd-III and Y-III complexes were assembled with dimeric {[Au(SCN)(2)](-)}(2) and trimeric {[Au(SCN)(2)](-)}(3) bis(thiocyanato)gold(I) counterions. The vibrational signature associated with the Au...Au vibrational mode was probed with ultralow frequency (ULF) Raman spectroscopy as a function of temperature. Emission spectroscopy was used to explore photophysical properties. Two broad features in the high- and lowenergy regions were associated with the fluorescence and phosphorescence of the gold entities, respectively. Temperature-dependent luminescence measurements showed that the emission color can be tuned from blue to green via cyan and white. Hence, these complexes can act as colorimetric thermometers. Additionally, a ratiometric thermal sensing ability was incorporated with high sensitivity up to 5 % K-1 in the cryogenic temperature range.

Automated summary

Gold complexes can form excimers and exciplexes under light excitation. By assembling different gold ions, the emission color can be tuned, enabling the complexes to function as colorimetric thermometers and ratiometric thermal sensors with high sensitivity.