A series of ruthenium complexes showing unique solvatochromism in the chlorido‐ligated form and reversible photoisomerization in the aqua‐ligated form has been developed. The complexes bear a tridentate ligand and a bidentate ligand containing naphthyridine and diethylamino moieties. In the chlorido complex, steric repulsion between the chlorido ligand and the diethylamino group promotes ligand‐substitution with solvent molecules in coordinating and protic solvents. The absorption maxima in the visible region shifted by approximately 120 nm depending on the solvent. The aqua complex exhibited intramolecular hydrogen bonding between the aqua and diethylamino moieties according to X‐ray crystallography. The photoisomerization behavior of the aqua complex was evaluated by 1 H nuclear magnetic resonance measurements. The quantum yield of photoisomerization was 2 × 10 −4 , which is much smaller than that of the complex without the diethylamino moiety, indicating that the hydrogen bonding hinders the photodissociation of the aqua ligand.
Osumi et al. (Thu,) studied this question.