Efficient Photoswitch System Combining a Dimethyldihydropyrene Pyridinium Core and Ruthenium(II) Bis-Terpyridine Entities

Terpyridine
ruthenium complexes linked to the dimethyldihydropyrene (DHP) photochromic
unit have been synthesized and fully characterized by cyclic voltammetry
and absorption and emission spectroscopy. The study of the photoisomerization
reaction undergone by the DHP motif under visible light irradiation
is reported. In comparison to previous work, the introduction of an
electron-withdrawing pyridinium spacer between the chelating terpyridine
unit and the DHP skeleton has considerably tuned the photochromic
properties of the free ligands and their corresponding complexes in
term of time response and photoreversibility. A rapid, reversible,
and complete conversion between the closed and the open forms has
been clearly evidenced under visible light irradiation. Only slight
perturbations have been induced by the presence of ruthenium centers.
Experimental findings and their interpretation have been supported
by theoretical calculations.