A DNA-Stabilized Ag-18(12+) Cluster with Excitation-Intensity-Dependent Dual Emission

DNA-stabilized silver nanoclusters (DNA-AgNCs) are easily tunable emitters with intriguing photophysical properties. Here, a DNA-AgNC with dual emission in the red and near-infrared (NIR) regions is presented. Mass spectrometry data showed that two DNA strands stabilize 18 silver atoms with a nanocluster charge of 12+. Besides determining the composition and charge of DNA(2)[Ag-18](12+), steady-state and time-resolved methods were applied to characterize the picosecond red fluorescence and the relatively intense microsecond-lived NIR luminescence. During this process, the luminescence-to-fluorescence ratio was found to be excitation-intensity-dependent. This peculiar feature is very rare for molecular emitters and allows the use of DNA(2)[Ag-18](12+) as a nanoscale excitation intensity probe. For this purpose, calibration curves were constructed using three different approaches based either on steady-state or time-resolved emission measurements. The results showed that processes like thermally activated delayed fluorescence (TADF) or photon upconversion through triplet-triplet annihilation (TTA) could be excluded for DNA(2)[Ag-18](12+). We, therefore, speculate that the ratiometric excitation intensity response could be the result of optically activated delayed fluorescence.

Automated summary

This article presents a DNA-stabilized silver nanocluster (DNA-AgNC) with dual emission in the red and near-infrared regions. Mass spectrometry data shows that two DNA strands stabilize 18 silver atoms with a nanocluster charge of 12+. Steady-state and time-resolved methods were used to characterize the red fluorescence and NIR luminescence, and the luminescence-to-fluorescence ratio was found to be excitation-intensity-dependent, making it a nanoscale excitation intensity probe.