Influence of Electron Acceptor and Electron Donor on the Photophysical Properties of Carbon Dots: A Comparative Investigation at the Bulk‐State and Single‐Particle Level

Abstract

Carbon dots (CDs) are extensively studied to investigate their unique optical properties such as undergoing electron transfer in different scenarios. This study presents an in-depth investigation to study the ensemble-averaged state/bulk state and single-particle level photophysical properties of CDs that have been passivated with electron-accepting (CD-A) and electron-donating molecules (CD-D) on their surface. Our ensemble-averaged state experiments including UV-Vis absorbance titrations, time-resolved photoluminescence (PL) spectra, and 2D emission studies depicted that both CD-A or CD-D had a blue-shift in emission, with a drastic increase in emission intensity, and consequently higher quantum yields, and that acceptor populations (CD-A) dominate overall photophysical properties. Interestingly, transmission electron microscopy and atomic force microscopy revealed that the mixing of donor and acceptor particles (CD-A+ CD-D) leads to a formation of at least two associated geometries, which was dependent on time, concentration, intramolecular electron/charge transfer and hydrogen bonding. On the other hand, single-particle studies revealed that the instantaneous intensity of CDs was comparable, but that CD-A and CD-D have a larger on-time duty cycle, attributed to an increase of blinking frequency. On-and off-time power-law analysis further revealed that CD-A has a larger off-time distribution slope than bare CDs, This article is protected by copyright. All rights reserved. 3 while their on-time distribution is similar. CD-D exhibits an increase in both on-and off-time distribution slope compared to bare CDs. These results indicate that the electron donor provides additional bright and dark states, while the electron acceptor primarily provides bright states, which can explain the increased blinking frequency in CD-A and CD-D at the single-particle level. Singleparticle studies, however, did not reveal an "acceptor-dominating" scenario based on analysis of instantaneous intensity, bleaching kinetics, and photoblinking, indicating that the direct interaction of CD-A and CD-D may affect their photophysical properties in the bulk state due to formation of hierarchical structural assemblies. We anticipate that these fundamental results will further provide insights towards our understanding of the complex mechanism associated with CD emission, which is one of the key contributors to their successful application. As an immediate application of these CDs, we have shown that they can be used as a sensing array for metal ions and can serve as a powerful toolbox for the technological application of CDs.

Polymer-Coated Nanoparticles for Therapeutic and Diagnostic Non-10B Enriched Polymer-Coated Boron Carbon Oxynitride (BCNO) Nanoparticles as Potent BNCT Drug

“…The photoluminescence (PL) spectra of the quasi-spherical BCNO nanoparticles with different polymer coating is presented in Figure 2. The PL spectra of the bare BCNO produced a broad emission with three bumps at 412 nm, 445 nm and 489 nm, which is consistent with literature reports [68,69]. Upon functionalization with PEG ligands, the photoluminescence spectra of PEG@BCNO remained the same compared to the PL spectra of bare BCNO nanoparticles.…”

Optically Controlled Supercapacitors: Functional Active Carbon Electrodes with Semiconductor Particles

“…The pores within the matrix of A-C are typically of submicron scale and, therefore, may be viewed as inverse Mie scatterers [ 21 , 22 ]. It is proposed that this unusual scattering effect is the result of coupling between the π–π* bonds at the interface of the A-C pores [ 23 ] and the electrolyte in the pore.…”

Emerging theranostic applications of carbon dots and its variants

“…48 The influence of both electron acceptor and electron donor on the photophysical properties of CDs were also investigated at the bulk-state and single-particle levels. 49 Lanthanides, for example, yttrium, were also doped in CDs to examine their influence on the photoluminescent properties and used for sensitive label-free detection of various pathogens at the single-cell resolution level. 50 A Mg/N codoping strategy was also developed to generate highly luminescent CQDs with a quantum yield of ∼83%.…”

“…164 CDs, on the other hand, present attractive PL and biocompatible features including intense fluorescence emission and fluorescence quenching when bound to target analytes, presence of targeting sites, variable emission spectra, and minimal cytotoxicity and are thus being considered as alternative options to pre-existing sensing probes. 49,165 Sensing of different anions, proteins, biomolecules based on fluorescence is a field of study gaining considerable attention. This method generates an output based on the differences in optical patterns from a sensor.…”