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The interaction of photoexcited Carbon nanodots with metal ions disclosed down to the femtosecond scale


Fluorescent Carbon nanodots are a novel family of carbon-based nanoscale materials endowed with an outstanding combination of properties that make them very appealing for applications in nanosensing, photonics, solar energy harvesting and photocatalysis. One of the remarkable properties of Carbon dots is their strong sensitivity to local environment, especially to metal ions in solution. These interactions provide a testing ground of their marked photochemical properties, highlighted by many studies, and frequently driven by charge transfer events. Here we combine several optical techniques, down to the femtosecond time resolution, to understand the interplay between Carbon nanodots and aqueous metal ions such as Cu2+ and Zn2+. We find that copper inhibits the fluorescence of carbon dots through static and diffusional quenching mechanisms, and our measurements allow discriminating between the two. Ultrafast optical methods are then used to address the dynamics of copper-dot complexes, wherein static quenching takes place, and unveil the underlying complexity of their photocycle. We propose an initial increase of electronic charge on the surface of the dot, upon photo-excitation, followed by a partial electron transfer to the nearby ion, with 0.2 ps and 1.9 ps time constants, and finally a very fast (<<1 ps) non-radiative electron-hole recombination which brings the system back to the ground state. Notably, we find that the electron transfer stage is governed by ultrafast water rearrangement around photo-excited dots, pointing out the key role of solvent interactions in the photo-physics of these systems.

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Publication details

The article was accepted on 05 Jun 2017 and first published on 07 Jun 2017

Article type: Paper
DOI: 10.1039/C7NR03754F
Citation: Nanoscale, 2017, Accepted Manuscript
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    The interaction of photoexcited Carbon nanodots with metal ions disclosed down to the femtosecond scale

    A. Sciortino, A. Madonia, M. Gazzetto, L. Sciortino, E. J. Rohwer, T. Feurer, F. Gelardi, M. Cannas, A. Cannizzo and F. Messina, Nanoscale, 2017, Accepted Manuscript , DOI: 10.1039/C7NR03754F

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