Modulation of the Photophysical Properties of 1‐Azathioxanthones by Eu3+, Gd3+, Tb3+, and Yb3+ Ions in Methanol

The design of bright fluorescent probes based on lanthanide centered emission relies on efficient energy transfer from antenna chromophores to lanthanide centers. Here, we set out to explore the excited state energy migration pathways using collisional quenching of three 1‐azathioxanthones by four lanthanide(III) ions. The results show that each combination of lanthanide(III) ion and chromophore must be considered as a unique case, as the rate constants that determine the outcome of the excited state energy migration is modulated differently in each system. For the three dye systems investigated here, the effect of the lanthanide(III) ions is that two dye systems show a strong increase in inter‐system crossing leading to increased fluorescence yields and room temperature phosphorescence, while the fluorescence is quenched in the third dye system. Contrasting our results with literature data leads us to conclude that freely diffusing dyes and ions do not shed light on which properties will be found for linked systems.