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.

Two‐Orders‐of‐Magnitude Enhancement of Photoinitiation Activity via a Simple Surface Engineering of Metal Nanoclusters

“…In early years, a major bottleneck for metal nanoclusters is that they have rarely demonstrated an unparalleled performance in certain critical applications that no other types of materials can compete. Thus, the recent research progress in the strong near‐infrared photoluminescence from the biocompatible gold and other nanoclusters, [35–55] as well as the high catalytic performance (e.g., CO 2 reduction) of Cu and other emerging nanoclusters [56–72] are very exciting. Different from above work, our previous work demonstrated the first application of metal nanoclusters in 3D laser printing [16] and current findings further manifest the capability of metal nanoclusters as unparalleled photoinitiation systems which could break though the current efficiency limit of 3D laser nanoprinting.…”

Fluorescence Screening of DNA-AgNCs with Pulsed White Light Excitation

“…11,28−31 Additionally, steady state approaches do not allow for discriminating between ns-and μs-lived emission, leading to potential misclassification of the training data for dual emissive DNA-AgNCs. 6,8,10,17,32,33 Here, we demonstrate a new technique for screening assynthesized DNA-AgNCs by exciting with the white light output (λ ex ≈ 490−900 nm) of a pulsed supercontinuum laser, which is used together with a common-path interferometer and timecorrelated single photon counting (TCSPC) board for spectrally and temporally resolving the DNA-AgNC emission, respectively. With white light excitation, the DNA-AgNCs are directly excited into their main AgNC-related band, rather than through the DNA-related UV band, providing a more relevant readout of DNA-AgNC emission when used with Vis/NIR excitation at a later stage.…”

Time gated Fourier transform spectroscopy with burst excitation for time-resolved spectral maps from the nano- to millisecond range

“…In this paper, we will describe the working principle of bmTG-FTS and demonstrate its applicability with an exemplary DNA-AgNC that shows dual emission on the nano-to millisecond timescale. 17 bmTG-FTS is based on three key elements: TCSPC hardware, an interferometer, and a high repetition laser (MHz) that can be switched on and off on a microsecond time scale. Using TCSPC, each detected photon is assigned a 'micro-time' and a 'macrotime' (Fig.…”

“…For the proof of principle demonstration of bmTG-FTS, we decided to investigate a dual emissive DNA-AgNC, which we recently reported. 17 This particular AgNC is stabilized by the DNA sequence, 5 0 -TGGACGGCGG-3 0 , and mass spectrometry revealed that the cluster has a molecular formula of (DNA) 2 [Ag 18 ] 12+ . 17 It has an absorption maximum at 543 nm and two emission bands, one associated with a ps decay and one with a ms decay.…”

“…17 This particular AgNC is stabilized by the DNA sequence, 5 0 -TGGACGGCGG-3 0 , and mass spectrometry revealed that the cluster has a molecular formula of (DNA) 2 [Ag 18 ] 12+ . 17 It has an absorption maximum at 543 nm and two emission bands, one associated with a ps decay and one with a ms decay. The ratio between the two peaks proved to be dependent on the excitation intensity, with the long-lived band decreasing at higher excitation intensities, which allowed for the realization of a molecular light intensity meter.…”