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Theoretical Investigations of Optical Origins of Fluorescent Graphene Quantum Dots.

Wang J, Cao S, Ding Y, Ma F, Lu W, Sun M - Sci Rep (2016)

Bottom Line: Surface functionalization with donor or acceptor groups produced a red shift in the absorption spectrum, and electrons and holes were highly delocalized.The recombination of excited, well-separated electron-hole (e-h) pairs can result in enhanced fluorescence.This fluorescence enhancement by surface functionalization occurs because of the decreased symmetry of the graphene resulting from the roughened structure of the surface-functionalized GQDs.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry and Department of Physics, Liaoning University, Shenyang 110036, PR China.

ABSTRACT
The optical properties of graphene quantum dots (GQDs) were investigated theoretically. We focused on the photoinduced charge transfer and electron-hole coherence of single-layer graphene in the electronic transitions in the visible regions. Surface functionalization with donor or acceptor groups produced a red shift in the absorption spectrum, and electrons and holes were highly delocalized. The recombination of excited, well-separated electron-hole (e-h) pairs can result in enhanced fluorescence. This fluorescence enhancement by surface functionalization occurs because of the decreased symmetry of the graphene resulting from the roughened structure of the surface-functionalized GQDs.

No MeSH data available.


Charge-transfer densities for the strong electronic transitions in the SF-GQD with -NH2, where the holes and electrons are represented in green and red, respectively.
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f4: Charge-transfer densities for the strong electronic transitions in the SF-GQD with -NH2, where the holes and electrons are represented in green and red, respectively.

Mentions: Therefore, all of the strong electronic transitions of-GQDs are charge-transfer excited states because the charge-transfer lengths of these excited states all exceed 2.0 Å. The CDDs of these excited states confirm this phenomenon; the holes and electrons are well separated, and the degree and orientation of the electron transfer are well visualized (Fig. 4). For example, for the electronic transition at 801 nm, almost all holes are localized on the edge, whereas the electrons are localized on the center. For the electronic transition at 611 nm, the holes are localized on the right edges, and the electrons are delocalized to the center of graphene and the left edges. This behavior means that in this excited state, the optical excitation occurs at the right edge, and then the electrons excited at this edge are delocalized to the other parts, indicating strong electron transfer in the excited state.


Theoretical Investigations of Optical Origins of Fluorescent Graphene Quantum Dots.

Wang J, Cao S, Ding Y, Ma F, Lu W, Sun M - Sci Rep (2016)

Charge-transfer densities for the strong electronic transitions in the SF-GQD with -NH2, where the holes and electrons are represented in green and red, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4837401&req=5

f4: Charge-transfer densities for the strong electronic transitions in the SF-GQD with -NH2, where the holes and electrons are represented in green and red, respectively.
Mentions: Therefore, all of the strong electronic transitions of-GQDs are charge-transfer excited states because the charge-transfer lengths of these excited states all exceed 2.0 Å. The CDDs of these excited states confirm this phenomenon; the holes and electrons are well separated, and the degree and orientation of the electron transfer are well visualized (Fig. 4). For example, for the electronic transition at 801 nm, almost all holes are localized on the edge, whereas the electrons are localized on the center. For the electronic transition at 611 nm, the holes are localized on the right edges, and the electrons are delocalized to the center of graphene and the left edges. This behavior means that in this excited state, the optical excitation occurs at the right edge, and then the electrons excited at this edge are delocalized to the other parts, indicating strong electron transfer in the excited state.

Bottom Line: Surface functionalization with donor or acceptor groups produced a red shift in the absorption spectrum, and electrons and holes were highly delocalized.The recombination of excited, well-separated electron-hole (e-h) pairs can result in enhanced fluorescence.This fluorescence enhancement by surface functionalization occurs because of the decreased symmetry of the graphene resulting from the roughened structure of the surface-functionalized GQDs.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry and Department of Physics, Liaoning University, Shenyang 110036, PR China.

ABSTRACT
The optical properties of graphene quantum dots (GQDs) were investigated theoretically. We focused on the photoinduced charge transfer and electron-hole coherence of single-layer graphene in the electronic transitions in the visible regions. Surface functionalization with donor or acceptor groups produced a red shift in the absorption spectrum, and electrons and holes were highly delocalized. The recombination of excited, well-separated electron-hole (e-h) pairs can result in enhanced fluorescence. This fluorescence enhancement by surface functionalization occurs because of the decreased symmetry of the graphene resulting from the roughened structure of the surface-functionalized GQDs.

No MeSH data available.