The ability of luminescent semiconductor quantum dots (QDs) to engage in
diverse energy transfer processes with organic
dyes, light-harvesting proteins, metal complexes,
and redox-active labels continues to stimulate interest in developing them for biosensing and
light-harvesting applications. Within biosensing configurations, changes in the rate of energy
transfer between the QD and the proximal donor, or acceptor, based upon some external
(biological) event form the principle basis for signal transduction. However, designing QD
sensors to function optimally is predicated on a full understanding of all relevant energy
transfer mechanisms. In this report, we examine energy transfer between a range of
CdSeZnS coreshell QDs and a redox-active osmium(II) polypyridyl complex. To facilitate
this, the Os complex was synthesized as a reactive isothiocyanate and used to label a
hexahistidine-terminated peptide. The Os-labeled peptide was ratiometrically self-assembled
to the QDs via metal affinity coordination, bringing the Os complex into close proximity of the
nanocrystal surface. QDs displaying different emission maxima were assembled with
increasing ratios of Ospeptide complex and subjected to detailed steady-state, ultrafast
transient absorption, and luminescence lifetime decay analyses. Although the possibility exists
for charge transfer quenching interactions, we find that the QD donors engage in relatively
efficient Förster resonance energy transfer with the Os complex acceptor despite relatively low
overall spectral overlap. These results are in contrast to other similar QD donorredox-active
acceptor systems with similar separation distances, but displaying far higher spectral overlap,
where charge transfer processes were reported to be the dominant QD quenching mechanism