Modulation of Photochemical Properties in Ion-Controlled Multicomponent Dynamic Devices

A bis-pyrenyl-terpyridine ligand 1 has been synthesised and used to prepare zinc homo- and heterocomplexes and their photophysical properties have been studied. Fluorescence titrations displayed modulation of absorption and emission, depending on the molarities of the ionic species (Zn2+, H+). Two single-crystal structures give insights into the formation of multicomponent supramolecular networks, also present in solution as shown by NMR and ESI-MS spectroscopy. NMR spectroscopy revealed fast exchanges of the ligands complexed around the metal ion, which could be reduced at lower temperature. Conformational (from W to U shape) and photophysical changes of the flexible ligand were demonstrated in the solid and liquid phases. Addition of zinc ions to the solution of ligands changes the absorption and fluorescence spectra noticeably. The zinc complexes do not form exciplexes; the fluorescence is mainly due to charge-transfer transitions. The present work illustrates the potential use of ion-triggered switches to generate mechanical motions that can be followed photophysically.