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Published on: June 10, 2021
Anion-specific fluorescence enhancement via counterion modulation in biphenyl-based porous cage salts
Rachel M Sabatino1, Merissa N Morey1, Alex Lovstedt1
1Department of Chemistry, Indiana University Bloomington IN 47405 USA edbloch@iu.edu.
Abstract:
Porous coordination cages offer a versatile platform for integrating photophysical functionality into well-defined molecular architectures; however, many widely studied cages are intrinsically non-emissive. Here, we report counterion-dependent fluorescence switching in biphenyl-functionalized zirconium porous cages, in which anion identity strongly influences emission behavior. The cage exhibits bright fluorescence when isolated as a chloride salt, while the corresponding triflate salt is essentially non-emissive despite the same underlying Zr-bpdc connectivity. Systematic counterion exchange and qualitative salt screening show that fluorescence enhancement from the triflate form depends chiefly on anion identity rather than the accompanying cation, with nitrate giving the largest enhancement. These results identify counterion modulation as a simple strategy for tuning fluorescence in zirconium porous cages and highlight the importance of anion identity in shaping their solid-state photophysical behavior.
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To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...

