Optically enhanced, near-IR, silver cluster emission altered by single base changes in the DNA template
Petty, J. T.; Fan, C.; Story, S. P.; Sengupta, B.; Sartin, M.; Hsiang, J.; Perry, J. W.; Dickson, R. M. Optically enhanced, near-IR, silver cluster emission altered by single base changes in the DNA template. J. Phys. Chem. B 2011, 115, 7996-8003.
Few-atom silver clusters harbored by DNA are promising fluorophores due to their high molecular brightness along with their long- and short-term photostability. Furthermore, their emission rate can be enhanced when co-illuminated with low-energy light that optically depopulates the fluorescence-limiting dark state. The photophysical basis for this effect is evaluated for two near-infrared-emitting clusters. Clusters emitting at âˆ¼800 nm form with C(3)AC(3)AC(3)TC(3)A and C(3)AC(3)AC(3)GC(3)A, and both exhibit a trap state with Î»(max) âˆ¼ 840 nm and an absorption cross section of (5-6) Ã— 10(-16) cm(2)/molecule that can be optically depopulated. Transient absorption spectra, complemented by fluorescence correlation spectroscopy studies, show that the dark state has an inherent lifetime of 3-4 Î¼s and that absorption from this state is accompanied by photoinduced crossover back to the emissive manifold of states with an action cross section of âˆ¼2 Ã— 10(-18) cm(2)/molecule. Relative to C(3)AC(3)AC(3)TC(3)A, C(3)AC(3)AC(3)GC(3)A produces a longer-lived trap state and permits more facile passage back to the emissive manifold. With the C(3)AC(3)AC(3)AC(3)G template, a spectrally distinct cluster forms having emission at âˆ¼900 nm, and its trap state has a âˆ¼4-fold shorter lifetime. These studies of optically gated fluorescence bolster the critical role of the nucleobases in both the formation and excited state dynamics of these highly emissive metallic clusters.
Journal of Physical Chemistry B