Supplementary Information

Quasi-Molecular Fluorescence from Graphene Oxide

Charudatta Galande1, Aditya D. Mohite2,*, Anton V. Naumov3,4, Wei Gao4, Lijie Ci1, , Anakha Ajayan1, Hui Gao1, Anchal Srivastava6, R.Bruce Weisman4 and Pulickel M. Ajayan1, 4,

*CorrespondingAuthor:

  1. Department of Mechanical Engineering and Materials Science, RiceUniversity, Houston, TX77005USA
  2. Center for Integrated Nanotechnologies and Chemistry Division, Los Alamos National Laboratory, Los Alamos, NM87545USA
  3. Applied Physics Program, RiceUniversity, HoustonTXUSA
  4. Department of Chemistry, RiceUniversity,HoustonTX USA
  5. Department of Physics, Banaras Hindu University, Varanasi, India.

Supplementary Fig. S- 1: Optical image of GO samples: Image of four GO suspensions at different pH values across the measured pH range. The suspensions progressively become darker as the pH increases and lighter as pH decreases. The suspension with highest pH is significantly darker, but not opaque.

Supplementary Figure S-2: TEM analysis of GO suspensions. (a) & (b): Representative TEM Images of GO flakes cast from tip sonicated suspensions (See Methods in main text). The GO flakes were single-layered and sizes as measured from TEM images was ranged between ~50-300 nm. (c) Typical selected area diffraction pattern taken on a single GO flake shows familiar hexagonal diffraction pattern of Graphene. The individual hexagonal pattern indicates the imaged GO piece is possibly single-layered [Nano Lett. 2010, 10, 1144] and implies good crystallinity in the sheets.

Supplementary Figure S-3:Gaussian fitting of fluorescence spectra. Fluorescence spectra (a) pH 8.0 and (b) pH 11.0 could be accurately simulated as a superposition of 5 Gaussians with coefficient of determination, R2>0.999 for all fits in basic regime. The basic peak positions deduced from these fits were 479 nm, 506 nm & 531 nm, with very small uncertainties (<0.25nm), while the broad weak acidic peaks had very large uncertainties.

For (c) pH 7.85 and (d) pH 6.5, the spectral weight of the 479 nm peak was negligible and the spectra could be accurately simulated by 4 Gaussians with R2>0.998. The corrected peak wavelengths for the broad acidic peaks were determined to be 577±13nm and 683±2 nm.

Supplementary Figure S-5: Fluorescence of GO prepared from expandable graphite. Fluorescence of GO synthesized from expandable graphite (see Methods) shows only one sharp peak (511 nm) at basic pH values, while showing broad, structure-less spectra in acidic medium.

Supplementary Figure S-6: Computed oscillator strengths for G-COOH and G-COO-optical transitions. Calculations were performed using the PM3 method for the graphene fragment shown in Fig. 5 of the main text.

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