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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 GQD, where the holes and electrons are represented in green and red, respectively.
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f3: Charge-transfer densities for the strong electronic transitions in the GQD, where the holes and electrons are represented in green and red, respectively.

Mentions: To reveal the nature of the optical origins of fluorescent GQDs, it is important to observe the e–h coherence and electron transfer in electronic transitions in the visible region. The degree of electron transfer determines the degree of fluorescence because the direct recombination of excited e–h pairs produces fluorescence24. We first demonstrate the degree and orientation of charge transfer for GQDs for strong electronic transitions. The charge difference densities (CDDs) in Fig. 3 reveal that the electrons and holes were locally excited and that the electrons transferred from the adjacent holes. Therefore, the electrons and holes were not significantly separated, and the degree of electron transfer from holes is weak because of the strong interaction between holes and electrons in the electronic transitions in the visible region. Note that electrons seem to significantly transfer from holes in the near-ultraviolet region (see CDD at 327.9 nm) but cannot contribute to the fluorescence in the visible region.


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 GQD, 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

f3: Charge-transfer densities for the strong electronic transitions in the GQD, where the holes and electrons are represented in green and red, respectively.
Mentions: To reveal the nature of the optical origins of fluorescent GQDs, it is important to observe the e–h coherence and electron transfer in electronic transitions in the visible region. The degree of electron transfer determines the degree of fluorescence because the direct recombination of excited e–h pairs produces fluorescence24. We first demonstrate the degree and orientation of charge transfer for GQDs for strong electronic transitions. The charge difference densities (CDDs) in Fig. 3 reveal that the electrons and holes were locally excited and that the electrons transferred from the adjacent holes. Therefore, the electrons and holes were not significantly separated, and the degree of electron transfer from holes is weak because of the strong interaction between holes and electrons in the electronic transitions in the visible region. Note that electrons seem to significantly transfer from holes in the near-ultraviolet region (see CDD at 327.9 nm) but cannot contribute to the fluorescence in the visible region.

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.