Abstract
Fluorescent organic dyes photobleach under intense light. Graphene has been shown to improve the photo-stability of organic dyes. In this paper, we investigated the Raman spectroscopy and photo-bleaching kinetics of dyes in the absence/presence of chemical vapor deposition (CVD)-grown graphene. We show that graphene enhances the Raman signal of a wide range of dyes. The photo-bleaching of the dyes was reduced when the dyes were in contact with graphene. In contrast, monolayer hexagonal boron nitride (h-BN) was much less effective in reducing the photo-bleaching rate of the dyes. We attribute the suppression of photo-bleaching to the energy or electron transfer from dye to graphene. The results highlight the potential of CVD graphene as a substrate for protecting and enhancing Raman response of organic dyes.
Highlights
It is generally known that organic dyes degrade upon intense light exposure
These results clearly indicate that the Raman enhancement induced by graphene is broadly applicable for many organic dyes.In addition, we compared the Raman signal of the fluorescein isothiocyanate (FITC) presented above and below the graphene (Figure 1a and Figures S3) and found that Raman signal of the dye was most intensive when the dye was covered with graphene
We found that the FITC dye decomposed faster in the presence of hexagonal boron nitride (h-BN) than in the presence of graphene, indicating the decrease of photo-bleaching rate of FITC dye by graphene is not mainly caused by the physical separation between the dye and oxygen
Summary
It is generally known that organic dyes degrade upon intense light exposure. During trace analysis by Raman spectroscopy, dyes need to be exposed to an intense laser for several to several tens of minutes. A number of studies have investigated the fluorescence quenching of organic dyes in the presence of exfoliated graphene and suggested that the quenching mechanism was energy or electron transfer between the dye and graphene [1]. The degree of Raman enhancement depends on both the electronic energy level alignment between the dye and graphene and the symmetry of the dye molecule, indicating that charge transfer is responsible for the enhancement [8] These early studies used high quality, almost defect-free exfoliated graphene. Zhao et al studied the surface-enhanced Raman spectroscopy of R6G dyes sandwiched between CVD-grown graphene and the magnetron sputtered Ag film They observed that the photo-stability of the dye was increased in the presence of graphene. We show that the fluorescence was quenched and the photo-bleaching rate was significantly slowed down by 46.3% in the presence of graphene
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