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 low-energy 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.