Supramolecular and Intramolecular Energy Transfer with Ruthenium-Anthracene Donor-Acceptor Couples: Salt Bridge versus Covalent Bond

The formation of hydrogen‐bonded cation–anion adducts between the complex [Ru(bpy)2(biimH2)]2+ (bpy = 2,2′‐bipyridine; biimH2 = 2,2′‐biimidazole) and anthracene‐9‐carboxylate in dichloromethane solution was investigated by 1H NMR, optical absorption, and luminescence spectroscopy. The experimental data indicates that more than one anthracene‐9‐carboxylate anion can interact closely with the dicationic ruthenium complex. Energy transfer from the photoexcited ruthenium complex to anthracene‐9‐carboxylate in 1:1 adducts of these two components was investigated by transient absorption spectroscopy and compared to intramolecular energy transfer in a covalently linked ruthenium‐xylene‐anthracene dyad with a comparable donor–acceptor distance. A ruthenium(II) biimidazole complex forms closely interacting cation–anion adducts with anthracene‐9‐carboxylate. Energy transfer within these adducts and a covalent donor‐bridge‐acceptor system is compared.