Facile and Reliable Emission-Based Nanomolar Anion Sensing by Luminescent Iridium Receptors Featuring Chelating Halogen-Bonding Sites.

An anion sensor is presented that combines a bidentate hydrogen- (HB) or halogen-bonding (XB) site with a luminescent monocationic Ir fragment for strong binding of common anions (Ka up to 6×104  m-1 ) with diagnostic emission changes. A new emission-based protocol for fast and reliable detection was derived on the basis of correction for systematic but unspecific background effects. Such a simple correction routine circumvents the hitherto practical limitations of systematic emission-based analysis of anion binding with validated open-source software (BindFit). The anticipated order of Ka values was obeyed according to size and basicity of the anions (Cl>Br=OAc) as well as the donor atom of the receptor (XB: 6×104  m-1 > HB: 5×103  m-1 ), and led to submicromolar limits of detection within minutes. The results were further validated by advanced NMR techniques, and corroborated by X-ray crystallographic data and DFT analysis, which reproduced the structural and electronic features in excellent agreement. The results suggest that corrected emission-based sensing may become a complementary, reliable, and fast tool to promote the use of XB in various application fields, due to the simple and fast optical determination at high dilution.