Efficient Photosensitizing Capabilities and Ultrafast Carrier Dynamics of Doped Carbon Dots

Abstract

Carbon dots (C-Dots) are promising new materials for the development of biocompatible photosensitizers for solar-driven catalysis and hydrogen production in aqueous solution. Compared to common semiconducting quantum dots, C-Dots have good physicochemical, as well as photochemical stability, optical brightness, stability and nontoxicity, while their carbon based source results in tunable surface chemistry, chemical versatility, low cost, and biocompatibility. Herein we show that doping the C-Dots with phosphate or boron significantly influences their excited-state dynamics, which is observed by the formation of a unique long-lived photoproduct as a function of the different dopants. To probe the photosensitizing capabilities of the C-Dots, we followed the photoreduction of methyl viologen (MV2+), which acts as a molecular redox mediator (electron acceptor) to the C-Dots (the photosensitizer, i.e., electron donor) in aqueous solution, using steady-state and time-resolved fluorescence and absorption spectroscopic techniques as well as electrochemical measurements. We show that ultrafast electron transfer to MV2+ and slow charge recombination results in a high quantum yield of MV2+ photoreduction, while the doping drastically influences this quantum yield of MV2+ radical. Our findings contribute to the photophysical understanding of this intriguing and relatively new carbon-based nanoparticle and can improve the design and development of efficient photosensitizers over commonly used heterogeneous catalysts in photocatalytic systems by increasing the efficiency of radical generation.

Enhanced Proton Conductivity across Protein Biopolymers Mediated by Doped Carbon Nanoparticles

“…Furthermore, the different doped C-Dots exhibit different FRET efficiencies, indicating that the binding interactions between the doped C-Dots and the BSA are being altered for the different doped C-Dots, whereas the NC-Dot-BSA mat exhibits the tightest binding of all other samples. As mentioned, the electronic properties of the C-Dots are highly dependent on the sp 3 /sp 2 carbon ratio within the C-Dot, which are different for the different doping, [15,16] and our results indicate that these differences highly influence the chemical interactions between the C-Dots and the BSA.…”

“…For the other two types of C‐Dots, we added either boron (in the form of sodium borate) or phosphorous (in the form of potassium phosphate) source during the synthesis of the nitrogen‐containing C‐Dot, hence creating boron or phosphorous doped C‐Dots (BC‐Dots and PC‐Dots, respectively). Although the different used C‐Dots here have different structural and electronic properties, [ 16 ] they all share a highly similar absorption spectrum ( Figure a). The surface functionalities and morphology of the different doped C‐Dots were determined using Fourier transform infrared (FTIR) and transmission electron microscope (TEM).…”

“…These different dopants can highly influence the (opto-)electronic properties of the C-Dots. [16,17] Another important structural feature of C-Dots is their surface functionalization in the form of carbon oxidation, meaning carboxyl and hydroxyl groups, as well as amines. These groups provide high solubility to the C-Dots and are probably related to the observed unique fluorescent properties of the C-Dots.…”

Long-range light-modulated charge transport across the molecular heterostructure doped protein biopolymers

“…The use of C-Dots is gaining high momentum in recent years, and it is considered a replacement for the traditional semiconductor quantum dot due to its high aqueous solubility, easy functionalization, low toxicity, and chemical inertness. [20][21][22][23][24] In terms of their ET properties, C-Dots have been used as both electron donors as well as electron acceptors. 20,[25][26][27][28][29] While we mainly use the C-Dot here as a photosensitizer, i.e., a light-induced electron donor, it is important to state that the type of C-Dot that we use here also acknowledges superior PT efficiency to the BSA mat.…”

“…[20][21][22][23][24] In terms of their ET properties, C-Dots have been used as both electron donors as well as electron acceptors. 20,[25][26][27][28][29] While we mainly use the C-Dot here as a photosensitizer, i.e., a light-induced electron donor, it is important to state that the type of C-Dot that we use here also acknowledges superior PT efficiency to the BSA mat. 16 Besides being the electron acceptor, the hemin is used here also as a molecular dopant for the BSA mat due to its strong binding affinity, as well as a charge mediator capable to support long-range ET whereas holes are the charge carriers.…”