Synthesis and electrochemical evaluation of 2‐substituted imidazolium salts

Abstract

Herein, we report the synthesis, electrochemical, and computational evaluation of six 2‐substituted imidazolium bromides and six 2‐substituted imidazolium triflates. All final compounds were obtained in 2 or fewer synthetic steps from inexpensive starting materials and display a single, irreversible electrochemical reduction. The reduction potentials span a range greater than 1 V depending on the electron withdrawing power of the 2‐substituent. Imidazolium bromides such as Bn2(H)ImBr reduce with E1/2 = −2.70 V vs Fc/Fc+, whereas the electron‐withdrawing Br‐containing analog Bn2(Br)ImBr reduces at only −1.58 V vs Fc/Fc+. The reduction potential of imidazolium bromides obeys a linear free energy relationship to σm Hammett constants, whereas imidazolium triflates correlate better with the σp Hammett constants. These results indicate that the stabilizing effect of the 2‐substituent is anion‐sensitive, changing from induction to resonance upon exchanging bromide for triflate. Predicted electron affinities from density functional theory–optimized structures of imidazolium cations and reduced species more closely match experimental data for the triflates, suggesting that a triflate anion does not electronically perturb the imidazolium core as much as a bromide. Taken together, these data highlight the dual modularity of imidazolium salts by changing both 2‐substituent and anion.

Mitochondria-Immobilized Unimolecular Fluorescent Probe for Multiplexing Imaging of Living Cancer Cells

“…The imidazolium salt is a cationic linker among fluorophores, which assists ZED to target mitochondria as well. It is also a probable mitochondria-immobilized group as imidazole and imidazolium salt can react with disulfide at 2-position, , and disulfide bonds are formed in the intermembrane space of mitochondria . Using imidazolium salt as a multifunctional linker among fluorophores simplifies molecular structure, shortens synthesis route, reduces molecular weight and improves water solubility, which provides an easy way to synthesize multifunctional probes.…”