Steady-state and time-resolved luminescence of Ru(II) polypyridine complexes attached to Ag nanoparticles: Effect of chemisorption in comparison with electrostatic bonding

• Luminescence of Ru(II)polypyridine complexes attached to Ag nanoparticles was studied.
• Surface plasmon extinction of Ag nanoparticles overlapped with the complex absorption.
• A decrease of 1MLCT to 3MLCT intersystem crossing efficiency was detected.
• The complex-Ag nanoparticle bonding affected the 3MLCT phosphorescence lifetimes.
• The 3MLCT lifetime of chemisorbed complex is 10× shorter than of the ion-paired one.

Steady state and nanosecond time resolved luminescence (namely, 3MLCT phosphorescence) of [Ru(bpy)3]2+ and of [Ru(bpy)2(dcbpy)]2+/bpy = 2,2′-bipyridine; dcbpy = 2,2′-bipyridyl-4,4′-dicarboxylic acid/attached to Ag NPs (the former by the electrostatic bonding, the latter by chemisorption) in non-aggregated Ag NP hydrosol systems has been investigated, and compared to the luminescence characteristics of the complexes in aqueous solutions. The intensity decrease of the 452 nm (and/or 455 nm, respectively) main band and elimination of the short wavelength shoulders in the excitation spectra and the intensity decrease of the emission spectra observed for both complexes upon their attachment to Ag NPs is attributed to the overlap of the excitation spectra with the surface plasmon extinction (SPE) of Ag NPs. The overlap leads to a loss of excitation energy by SPE as well as to a decrease of the 1MLCT to 3MLCT intersystem crossing efficiency. The time-resolved luminescence study shows that the 3MLCT phosphorescence lifetimes of both complexes are markedly (by 3 and 4 orders of magnitude, respectively) shortened upon their attachment to Ag NPs. Nevertheless, the 3MLCT lifetime of the chemisorbed [Ru(bpy)2(dcbpy)]2+ is by at least one order of magnitude shorter than that of the electrostatically bonded [Ru(bpy)3]2+, which indicates, that the phosphorescence lifetimes of these luminophores are strongly affected by the type of Ag NP surface–luminophore bonding.

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