Energy Transfer from Luminescent Porous Silicon to Adsorbed Osmium(II) and Ruthenium(II) Polypyridyl Complexes

摘要

Surface adsorption of transition-metal polypyridyl complexes on highly luminescent, anodized porous silicon (p-Si) wafers leads to dramatic quenching of the emission. Facile energy transfer occurs from the surface to adsorbed complexes of Ru~(II) and Os~(II). Photoluminescence (PL) from underivatized p-Si is excitation- and monitoring-wavelength-dependent. A phenomenological model is proposed to explain these observations in which intercluster energy transfer occurs by an energy-transfer cascade, and there is weak kinetic coupling to even lower-energy surface emitters. Adsorption of [Zn(dmb)_3](PF_6)_2 (dmb is 4,4'-dimethyl-2-2,2'-bipyridine) or fac-[Re(bpy)(CO)_3(4-Etpy)](PF_6)_2 (bpy is 2,2'-bipyridine; 4-Etpy is 4-ethylpyridine), possibly by ion-exchange, results in quenching of the low-energy surface emitters. For adsorbed [M~(II)(bpy)_2(4-CO_2H-4'Mebpy)](PF_6)_2 (M = Ru, Os; 4-CO_2H-4'Mebpy is 4-carboxylic acid-4'-methyl-2,2'-bipyridine), p-Si~* → M~(II) energy transfer occurs to low-lying metal-to-ligand charge-transfer (MLCT) excited states on the complexes as revealed by excitation and emission measurements. Energy transfer is efficient (>90%) and more rapid for Os~(II) (k_(en) ≈ 6 * 10~6 s~(-1)) than for Ru~(II) by a factor of ～10, consistent with a decrease in driving for p_Si~* → M~(II) energy transfer.