A DNA‐Stabilized Ag₁₈¹²⁺ Cluster with Excitation‐Intensity‐Dependent Dual Emission

Abstract

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 DNA₂[Ag₁₈]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 DNA₂[Ag₁₈]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 DNA₂[Ag₁₈]¹²⁺. We, therefore, speculate that the ratiometric excitation intensity response could be the result of optically activated delayed fluorescence.