Hydration Sensitive Orthogonal Dual Emission of a DNA-Stabilized Silver Nanocluster

DNA-stabilized silver nanoclusters (DNA-AgNCs) are a class of emitters that have primarily been studied for their molecular-like photophysical properties with ns-lived fluorescence. However, µs-lived luminescence has recently been reported for an increasing number of DNA-AgNCs, but little is still known about the origin of the long-lived emission. To deepen the understanding of the long-lived state, (DNA)₂-[Ag₁₁]⁷⁺, an emitter with short- and long-lived dual emission, is studied. By examining crystals of (DNA)₂-[Ag₁₁]⁷⁺, it is found that the fluorescence and luminescence transitions are orthogonal to each other, which implies that components orthogonal to the long axis of the AgNC, such as the nucleobases, contribute significantly to the polarization character of the long-lived luminescent state. The effect of the hydration level on the dual emission of dried (DNA)₂-[Ag₁₁]⁷⁺ droplets is also investigated, and it is found that water drastically reduces emission from the long-lived state and causes a redshift of the emission. Finally, an unusual excitation intensity-dependent response of dried (DNA)₂-[Ag₁₁]⁷⁺ droplets is noticed. This is ascribed to the heterogeneous local environment of the amorphous solid resulting in different conformations of (DNA)₂-[Ag₁₁]⁷⁺ with different optically activated delayed fluorescence probabilities. The presented results provide new key insights into the nature of the long-lived state of DNA-AgNCs.