Efficient Energy Transfer between Silicon Nanoparticles and a Ru-Polypyridine Complex

Blue-emitting amine-terminated Si nanoparticles (NPs; size, 1.57 +/- 0.24 nm) are functionalized with a Ru(bpy)(2)(spb)(2+) [bpy = 2,2'-bipyridine; spb = 4-(p-N-succinimidylcarboxyphenyl)-2,2'-bipyridine] complex. The distance between the dye and the Si core is controlled by different alkyl chain lengths (-C3H6, -C6H12, and -C11H22), and the thus formed Si NPs are two-chromophore systems that exhibit dual-emission in two separate regions: blue (similar to 450 nm, from Si core) and red (similar to 630 nm, from Ru dye). By measuring the Si/Ru ratio, the extinction coefficient of amino-terminated Si NPs was experimentally determined for the first time (2.6 x 10(5) M-1 cm(-1)). Energy transfer from Si NPs to acceptor molecules [Ru(bpy)(2)(spb)(2+)] is observed by steady-state and time-resolved fluorescence, and its distance-dependent efficiency is shown to be up to 55% in the case of a short alkyl spacer (-C3H6). Energy transfer rates are for all examined cases in the (0.2-2.2) x 10(9) s(-1) range.