Osmium–terpyridine complexes linked with stilbene-coupled naphthalene, anthracene, and pyrene moieties act as multichannel sensors for F− and Hg2+via non-classical interactions

Abstract

Fluoride (F⁻) and mercuric (Hg²⁺) ion sensing behaviours of homoleptic Os(II)–terpyridine complexes coupled with stilbene-appended naphthalene, anthracene and pyrene motifs have been thoroughly investigated here through the intermediacy of multiple non-covalent interactions such as CH⋯F hydrogen bonding, anion–π and cation–π interactions. The interaction event is monitored by absorption, steady state and time-resolved emission, and ¹H, ¹⁹F and ¹³C NMR spectroscopy. The stilbene units in the complexes enable trans–trans (t–t) to cis–cis (c–c) photoisomerization upon exposure to light, accompanied by substantial reorientation of their molecular backbone. In order to examine the efficiency of the conformational change in the ion binding characteristics, both anion and cation sensing investigations are also conducted on the c–c form of the complexes. Substantial alteration in sensing efficacy is indeed observed on passing from the t–t to the c–c forms of the complexes, highlighting the role of conformation changes in the ion–receptor interactions. The ion sensing efficacy of the trans–trans (t–t) forms is found to be higher relative to their cis–cis (c–c) counterparts. Parallel to the experimental study, computational investigations were also conducted on the t–t and c–c conformers of the complexes to elucidate various non-covalent interactions that are operative during the interplay among the complexes with both F⁻ and Hg²⁺ ions.