Photophysics of supercomplexes. A laser-induced optoacoustic study of the adducts between Ru(bpy)(CN)42− and polyaza macrocycles

In aqueous solution, the energy content of the triplet metal-to-ligand charge transfer (3MLCT) state, as determined by laser-induced optoacoustic spectroscopy, for both 1:1 supercomplexes {[Ru(bpy)(CN)4]·[24]ane-[N6H6]}4+ and {[Ru(bpy)(CN)4]·[32]ane-[N8H8]}6+ are similar to that for free Ru(bpy)(CN)42− (223±8 kJ/mol). The reduction of the structural volume change upon formation of the 3MLCT state in the order Ru(bpy)(CN)42− (14.9 ml/mol), {[Ru(bpy)(CN)4]·[32]ane-[N8H8]}6+ (5.2 ml/mol) and {[Ru(bpy)(CN)4]·[24]ane-[N6H6]}4+ (2.5 ml/mol) is attributed to the rigidity of the macrocycle cavity. The 3MLCT state lifetime increase from 104 ns for Ru(bpy)(CN)42− to 150 ns for {[Ru(bpy)(CN)4]·[24]ane-[N6H6]}4+ and 182 ns for {[Ru(bpy)(CN)4]·[32]ane-[N8H8]}6+ is due to the decrease in the number of CN groups free to form hydrogen bonds with water: four, one, and none, respectively.