Photochromic Dithienylethene- Phenanthroline Ligands and their Corresponding Ru(II) Complexes

Abstract

Dithienylethene-phenanthroline ligands as new photochromic systems are described. The photochemical and photophysical properties are strongly influenced by the substituents on the thiophene moiety. The photochromic properties are lost, if one or two methyl groups in position 2 and/or 2' of the target molecules (2o, 3o, 4o) are replaced by isopropyl groups. Replacement of a methyl group by a phenyl group in position 5 and/or 5' shifts the absorption maxima from 514 nm to 575 nm for the free ligand (1c, 2c) and from 530 nm to 613 nm for the corresponding ruthenium complex (Ru(1c), Ru(2c)) in its closed form. Unfortunately, the photochromic unit in its closed form can be reopened by a back reaction in the dark at room temperature. Complex Ru(2o) shows an emission with a maximum at 608 nm. The emission is quenched if the metal complex is in its closed form (Ru(2c)). Fatigue resistance is better for complex Ru(2o) than for the free ligand (2o).