Luminescent Ruthenium-Terpyridine Complexes Coupled with Stilbene-Appended Naphthalene, Anthracene, and Pyrene Motifs Demonstrate Fluoride Ion Sensing and Reversible Trans-Cis Photoisomerization.

Abstract

A new family of luminescent heteroleptic Ru(II)-terpyridine complexes coupled with stilbene-appended naphthalene, anthracene, and pyrene motifs is reported. Each of the complexes features moderately intense emission at room temperature having a lifetime of 16.7 ns for naphthalene and 11.4 ns for anthracene, while a substantially elevated lifetime of 8.3 μs was observed for the pyrene derivative. All the three complexes display a reversible couple in the positive potential window due to Ru2+/Ru3+ oxidation but multiple reversible and/or quasi-reversible peaks in the negative potential domain because of the reduction of the terpyridine moieties. All the complexes selectively sense F- among the studied anions via the intermediary of different noncovalent interactions. The interaction event is monitored through absorption, emission, and 1H and 19F NMR spectroscopy. Additionally, upon utilizing the stilbene motif, reversible trans-cis isomerization of the complexes has been undertaken upon alternate treatment of visible and UV light so that the complexes can act as potential photomolecular switches. We also carried out the anion sensing characterization of the cis form of the complexes. Theoretical calculation employing density functional theory is also executed for a selective complex (naphthalene derivative) to elucidate different noncovalent interactions that are operative during the complex-fluoride interplay.