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 ((MLCT)-M-3) 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 Ku(bpy)(CN)(4)(2-) (223 +/- 8 kJ/mol). The reduction of the structural volume change upon formation of the 3MLCT state in the order Ru(bpy)(CN)(4)(2-) (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 (MLCT)-M-3 state lifetime increase from 104 ns for Ru(bpy)(CN)(4)(2-) 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. (C) 2000 Elsevier Science B.V. All rights reserved.