A Macrocyclic 2,2′-Bibenzimidazole Ruthenium(II) Chromophore as a Versatile Building Block for Supramolecular Devices

Optical Sensing of Anions via Supramolecular Recognition with Biimidazole Complexes

Phosphorescent metal complexes with peripheral N-H donor functionalities have attracted great attention as potential molecular sensing units for anionic species lately. In this contribution we discuss the development and potential of anion recognition and sensing features of recent examples of luminescent 2,2'-biimidazole complexes of ruthenium(II), iridium(III), osmium(II) and cobalt(III). The general dependency of photophysical features in these complexes regarding the acid-base chemistry of the peripheral N-H functionalities will be outlined as a basic requirement for optical ion recognition. Systematic strategies for the tuning and specific improvement by synthetic means will be discussed regarding recent reports. With respect to their distinct photophysical features, different transition metals are considered individually to demonstrate particular trends regarding ligand modification within the respective groups. In summary, this review elucidates the current state-of-the-art and future potential of the versatile class of 2,2'-biimidazole based sensor chromophores.

A supramolecular H-bond driven light switch sensor for small anions

A cationic iridium complex with a 2,2'-bibenzimidazole ligand can act as a luminescent sensor for various anions. Strong H-bond supported ion pair bonding with an electron accepting dinitro-benzoate anion switches the luminescence "off". The luminescence of the sensor is switched back "on" when benzoate is replaced by competing H-bonded small anions, therefore leading to an enhanced sensitivity of the sensor system.