Biological Application of Luminescent Graphene Quantum Dots

Peng, Juan; Guan, Jufang; Jiang, Liping; Zhu, Jun

doi:10.1166/sam.2015.2259

Cited by 6 publications

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“…They have become thoroughly studied molecular systems due to their exceptional optical properties, stability, and easy surface modification, ,− which can be utilized in many applications. Their biocompatibility has made them promising nontoxic materials in the field of bioimaging, biosensors, and drug delivery. ,,− They have also received a lot of attention as potential photovoltaic devices and light emitting diodes (LED). ,− Chemical studies and tests show that they are useful also in magnetic fluorescence and two-photon fluorescence . CD structures are manifested by photoluminescence ranging from ultraviolet (UV) to infrared (IR) spectral regions with quantum yields up to 80–90%. ,, A variety of techniques ,− have been used to uncover their properties, such as their structure and morphology ,, and complex photoluminescence properties demonstrated by a different response to the excitation wavelength, showing both excitation-dependent and excitation-independent emission. ,, Their complexity results mainly from a substantial diversity of their sizes, ,, doping, − and functionalization, ,− the latter forming carbon sp 2 /sp 3 hybridized islands of variable sizes. ,, The still deficient control of these parameters contributes to controversies about the origin of the CD’s photoluminescence.…”

Section: Introductionmentioning

confidence: 99%

Conformational Behavior and Optical Properties of a Fluorophore Dimer as a Model of Luminescent Centers in Carbon Dots

et al. 2020

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The explanation of the origin of the fluorescence properties of carbon dots (CDs) represents an important task because of the great interest in the promising capabilities of these nanomaterials. 5-Oxo-1,2,3,5-tetrahydroimidazo-[1,2-α]-pyridine-7-carboxylic acid (IPCA), a molecular fluorophore, which is being created during the synthesis of CDs from citric acid and ethylenediamine, has been identified as an origin for the fluorescence of CDs. Using a combination of computational methods, we analyzed the UV absorption and fluorescence properties of the IPCA monomer and stacked IPCA dimers as basic models for the fluorescent centers in CDs. Density functional theory (DFT) for the ground state and time-dependent DFT calculations for excited states have been performed for the gas phase and for aqueous solution using a polarized continuum model. Classical molecular dynamics (MD) simulations of the dimer in the ground state have been carried out as well to investigate spontaneous association processes of IPCA and to analyze the ground state dynamics. Due to the complex charge distribution of the monomer and various possibilities of forming hydrogen bonds, in total, seven dimer structures have been identified at the DFT level as ground state minima with similar energies. Stabilities have been confirmed by domain-based local pair natural orbital (DLPNO) coupled cluster with singles and doubles and perturbative triples CCSD(T) calculations. The MD simulations confirm this picture, showing rotational flexibility processes of the two monomers with respect to each other. The lowest excited states have been characterized in terms of their orbital excitations and excitonic splitting. These calculations demonstrate the dominance of monomer π → π* transitions for the explanation of the observed UV spectra. Optimization of the dimer in the excited state did not lead to well-defined single structures but shows the picture of either intersection pathways to S1/S0 crossings which would quench fluorescence or stacked dimers with red-shifted fluorescence in comparison to the UV absorption. In the gas phase, both types of processes have been observed, whereas in solution only the stacked structures were found without any non-adiabatic radiationless deactivation processes.

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