Photobleaching and Recovery Kinetics of a Palette of Carbon Nanodots Probed by In Situ Optical Spectroscopy

Abstract

Carbon dots (CDs) are a family of fluorescent nanoparticles displaying a wide range of interesting properties, which make them attractive for potential applications in different fields like bioimaging, photocatalysis, and many others. However, despite many years of dedicated studies, wide variations exist in the literature concerning the reported photostability of CDs, and even the photoluminescence mechanism is still unclear. Furthermore, an increasing number of recent studies have highlighted the photobleaching (PB) of CDs under intense UV or visible light beams. PB phenomena need to be fully addressed to optimize practical uses of CDs and can also provide information on the fundamental mechanism underlying their fluorescence. Moreover, the lack of systematic studies comparing several types of CDs displaying different fluorescence properties represents another gap in the literature. In this study, we explored the optical properties of a full palette of CDs displaying a range from blue to red emissions, synthesized using different routes and varying precursors. We investigated the photostability of different CDs by observing in situ their time-resolved fluorescence degradation or optical absorption changes under equivalent experimental conditions and laser irradiation. The results about different PB kinetics clearly indicate that even CDs showing comparable emission properties may exhibit radically different resistances to PB, suggesting systematic connections between the resistance to PB, the characteristic spectral range of emission, and CD quantum yields. To exploit the PB dynamics as a powerful tool to investigate CD photophysics, we also carried out dedicated experiments in a partial illumination geometry, allowing us to analyze the recovery of the fluorescence due to diffusion. Based on the experimental results, we conclude that the nature of the CD fluorescence cannot be solely ascribable to small optically active molecules free diffusing in solution, contributing to shed light on one of the most debated issues in the photophysics of CDs.

Photoluminescence quantum yield of carbon dots: emission due to multiple centers versus excitonic emission

“…It has been reported that carbon nanomaterials, including carbon nanodots 44 and carbon nanotubes, 45 undergo photoinduced bleaching, demonstrating temporal evolution of PL with similar time constants in the range of 20-60 s, which was assigned to photooxidation processes. Zhang et al reported photoinduced bleaching of carbon dots due to the photoinduced dehydration of the deprotonated surface of CDs in dimethyl sulfoxide.…”

Recent progress of emitting long-wavelength carbon dots and their merits for visualization tracking, target delivery and theranostics

“…In order to probe the relevant mechanisms of fluorescence stability, Terracina et al investigated the photostability of LW-CDs by in situ observing their time-resolved fluorescence degradation or light absorption changes under equivalent experimental conditions and laser irradiation. It was found that the interaction between the fluorescent unit and the carbonaceous CD core not only affects the excited state decay properties of the former, but also has a protective effect on photobleaching 127 . In addition, the study found that the chemically inert emissive aromatics as the center can prevent the photochemical reaction and structural damage of the LW-CDs.…”

An overview on animal/human biomass-derived carbon dots for optical sensing and bioimaging applications

“…2), such as multicolor photoluminescence (PL), 8,9 chemical inertness, 10 and resistance to photo-bleaching. 11 Additionally, the aqueous/organic solvent dispersibility, high quantum yield (QY), low toxicity, good biocompatibility, and relatively inexpensive source for the lowcost, green synthesis of CDs further amplied their interest as an economical and environmentally sustainable class of uorescent nanomaterials. 7,9,[12][13][14][15] Consequently, the utility of CDs have been proven for diverse applications, including solar cells, 16 optoelectronic devices, 17 biosensing 18 and chemical/ metal sensing, 19,20 antibacterial agents, 21 photocatalysis and electrocatalysis, 22 displays, 23 nanothermometers, 24 drug delivery, 25 energy storage, 26 and live cell bioimaging 27 (Fig.…”