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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.


Optimized molecular structures.(a) GQD and (b) SF-GQD with -NH2.
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f5: Optimized molecular structures.(a) GQD and (b) SF-GQD with -NH2.

Mentions: The surface functionalization of GQDs can result in a red shift in the absorption spectrum and a corresponding red shift in the fluorescence spectrum. Our theoretical calculations are consistent with the experimental results. The CDDs in Fig. 4 reveal that the mechanism of fluorescence enhancement is not, as expected, mainly attributable to the functionalized donor or acceptor groups because both electrons and holes exist on the functionalized -NH2. To further reveal the mechanism of fluorescence enhancement by surface functionalization, we also obtained the optimized molecular geometries of GQDs and SF-GQDs with -NH2 (see Fig. 5). The optimized GQD geometry was found to be flat, whereas the optimized F-GQD geometry was not highly flattened, thereby decreasing the symmetry of the graphene. Therefore, the holes can be localized on the edge of the SF-GQD, and the electrons can transfer to other parts.


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)

Optimized molecular structures.(a) GQD and (b) SF-GQD with -NH2.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f5: Optimized molecular structures.(a) GQD and (b) SF-GQD with -NH2.
Mentions: The surface functionalization of GQDs can result in a red shift in the absorption spectrum and a corresponding red shift in the fluorescence spectrum. Our theoretical calculations are consistent with the experimental results. The CDDs in Fig. 4 reveal that the mechanism of fluorescence enhancement is not, as expected, mainly attributable to the functionalized donor or acceptor groups because both electrons and holes exist on the functionalized -NH2. To further reveal the mechanism of fluorescence enhancement by surface functionalization, we also obtained the optimized molecular geometries of GQDs and SF-GQDs with -NH2 (see Fig. 5). The optimized GQD geometry was found to be flat, whereas the optimized F-GQD geometry was not highly flattened, thereby decreasing the symmetry of the graphene. Therefore, the holes can be localized on the edge of the SF-GQD, and the electrons can transfer to other parts.

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.