Triplet-triplet annihilation of excited states of polypyridyl Ru(II) complexes bound to polystyrene

Femtosecond transient absorption spectroscopy is used to study the triplet-triplet annihilation (TTA) interaction between the metal-to-ligand charge-transfer (MLCT) excited states of Ru(II) polypyridyl complexes bound to a polystyrene backbone. The polymer chains have, on average, 20 repeat units, each functionalized with a transition metal complex. Spectroscopic experiments are performed on assemblies dissolved in acetonitrile at room temperature. The time-resolved spectra show kinetics that depend on the intensity of the excitation laser. These effects are attributed to the interaction between multiple excited states formed on a single chain. Fast and slow (intensity-dependent) kinetic components are observed. The fast 3 ps) component is assigned to the TTA of MLCT excited states formed at adjacent sites within the assembly, while the slow component is attributed to TTA between excited states that must undergo energy migration prior to annihilation. Femtosecond experiments are also performed on Ru(bpy)(3)(2+) (bpy = 2,2'-bipyridine) and a mixed-ligand Ru(11) complex that serves as a reference system for the polymer.