Supporting Information to Carbon Nanodots Towards a Comprehensive Understanding of their Photoluminescence

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1 Supporting Information to Carbon Nanodots Towards a Comprehensive Understanding of their Photoluminescence Volker Strauss, a, Johannes T. Margraf, a,b, Christian Dolle, c Benjamin Butz, c Thomas J. Nacken, d Johannes Walter, d Walter Bauer, e* Wolfgang Peukert, d* Erdmann Spiecker, c* Timothy Clark, b* Dirk M. Guldi a* Table of Contents General...2 XRD and IR Spectroscopy...3 Zeta-Potential...4 Thermogravimetric Analysis-Mass Spectrometry...5 NMR Spectroscopy...6 Analytical Ultracentrifugation Transmission Electron Microscopy Atomic Force Microscopy Steady State Absorption and Emission Spectroscopy Time Resolved Emission Spectroscopy Transient Absorption Spectroscopy Calculated IR-Spectra Calculated UV-Vis Spectra Triplet State of CND1 hydroxy Simulated Luminescence Spectra and Decays Quenching Experiments with Emission Up-conversion Spectroscopy Steady State Quenching Lifetimes S 1

2 General Figure S1. Photographs of visible light and 366 nm illuminated pcnd solutions. S 2

3 XRD and IR Spectroscopy Figure S2. Top: Powder XRD spectrum of dry pcnds. Bottom: ATR-IR spectrum of pcnds in aqueous solutions. S 3

4 Zeta-Potential Zeta potentials were determined using a Zetasizer Nano ZEN3600 (Malvern Instruments) using aqueous CND solutions of equal concentrations. Figure S3. ζ-potential of pcnd in H2O in the presence of different concentrations of MV 2+. S 4

5 Thermogravimetric Analysis-Mass Spectrometry Mass spectrometry coupled thermogravimetric analysis (TGA-MS) was performed with a Netzsch STA 409 CD instrument and a Skimmer QMS 422 mass spectrometer (MS/EI). Figure S4. Thermogravimetric analysis (20K/min) coupled with mass spectrometry of acnd (black) and pcnd (red) under an inert He atmosphere. S 5

6 NMR Spectroscopy Figure S5. Liquid state 1 H-NMR spectrum, D2O, +26 o C, 32k data points, 16 scans, acquisition time 3.3 sec., relaxation delay 2.0 sec. Note the lack of signals in the aromatic region around 7.3 ppm, indicating the lack of protonated ring carbons. Also note the lack of signals for CH3-groups with non-electron withdrawing groups. S 6

7 Figure S6. Liquid state 13 C{ 1 H}-NMR spectrum, D2O, +26 o C, 32k data points, scans, acquisition time 0.97 sec., relaxation delay 5.0 sec. Note the presence of signals for quaternary aromatic ring carbons as well as signals for various carbonyl groups. S 7

8 Figure S7. Solid state 13 C{ 1 H}-NMR spectrum, +26 o C, TOSS pulse sequence (TOSS = Total Suppression of Spinning Side Bands), spinning speed 4424 Hz, 2k data points, zero filled to 8k, scans, acquisition time 41 msec., relaxation delay 10.0 sec. Note the presence of signals for quaternary ring carbons as well as for carbonyl groups. S 8

9 Figure S8. Solid state 13 C{ 1 H}-NMR spectrum, +26 o C, TOSS-delay pulse sequence (TOSS = Total Suppression of Spinning Side Bands, delay = dephasing delay between end of TOSS sequence and begin of acquisition), spinning speed 4712 Hz, 2k data points, zero filled to 8k, scans, acquisition time 41 msec., relaxation delay 10.0 sec., dephasing delay 0.05 msec. The employed pulse sequence suppresses signals of CH and CH2 groups. S 9

10 Analytical Ultracentrifugation Figure S9. Top: Experimental data (blue) and fit (red) for the CNDs experiment. Middle: Residuals bitmap of the best fit illustrating that random noise is obtained for the data analysis. Bottom: Residuals data of the 2DSA-MC analysis with a total RMSD value of OD. S 10

11 Transmission Electron Microscopy Transmission electron microscopy was conducted with an aberration-corrected Titan³ (FEI Company) at accelerating voltage of 200 kv. The spherical aberration (C S ) was tuned to be negative but not lower than -5 µm to enhance the contrast transfer by negative C s imaging (NCSI). Samples were prepared by dispersing a solution of CNDs in water or aceton and placing a drop of the solution on a TEM grid covered by an ultrathin carbon support film (on holey carbon film). The samples were dried in a desiccator investigated. Due to the nature of the CNDs (missing crystalline order, cf. electron diffraction pattern) no scattering contrast was expected. Fig. S9 shows representative HRTEM images with intensity variations from highly amorphous material without detectable crystalline structure. Figure S10. HRTEM at magnification of a) 165 kx and b) 340 kx. No crystalline structures can be identified, c) selected-area electron diffraction pattern shows no distinct crystalline order. S 11

12 Atomic Force Microscopy Figure S11. Typical AFM image of pcnds on a Si/SiO2 wafer µm. S 12

13 Steady State Absorption and Emission Spectroscopy Figure S12. Left: Normalized absorption spectra of pcnd (red) and acnd (black) in aqueous solutions at room temperature. Right: Normalized luminescence spectra of pcnd (red) and acnd (black) in aqueous solutions upon 350 and 410 nm excitation at room temperature, respectively. Figure S13. 3D-luminescence plot of acnd in aqueous solutions at room temperature with increasing intensity from blue to green and to red. S 13

14 Time Resolved Emission Spectroscopy Figure S14. Top: Time-luminescence profiles obtained by means of time-resolved emission spectroscopy (TRES) of pcnd in aqueous solutions in the wavelength range between 400 and 550 nm. Bottom: Time-resolved emission spectra (TRES) obtained upon excitation (403 nm) of pcnd in aqueous solutions. S 14

15 Transient Absorption Spectroscopy Figure S15. Top: Differential absorption spectra obtained upon femtosecond flash photolysis (387 nm) of pcnd in aqueous solutions with several time delays between 0 and 2000 ps at room temperature. Bottom: Time-absorption profiles of the spectra shown on the top at 625 nm. S 15

16 Calculated IR-Spectra Figure S16. Simulated IR-spectrum for CND1, at the ωb97x-d/def2-sv(p) level. S 16

17 Calculated UV-Vis Spectra Table S1. Predicted optical properties of CND model systems employing UNO-CIS/PM3. Model λabs [nm] λem [nm] kr [ 10 5 s -1 ] CND CND CND1bilayer CND1epoxy CND1hydroxy CND1pyridine Figure S17. Simulated UV-Vis spectrum of CND1. S 17

18 Figure S18. Simulated UV-Vis spectrum of CND2. Figure S19. Simulated UV-Vis spectrum of CND1bilayer. Figure S20. Simulated UV-Vis spectrum of CND1epoxy. S 18

19 Figure S21. Simulated UV-Vis spectrum of CND1hydroxy. Figure S22. Simulated UV-Vis spectrum of CND1pyridine. S 19

20 Triplet State of CND1hydroxy The low lying triplet state of CND1hydroxy is formed by a HOMO-LUMO excitation from the ground-state singlet. The orbitals involved are plotted below: Figure S23. Left: HOMO isosurface (0.03 e - A -3 ) of CND1hydroxy. Right: LUMO isosurface (0.03 e - A -3 ) of CND1hydroxy. S 20

21 Simulated Luminescence Spectra and Decays Figure S24. The spectral distribution and calculated Einstein coefficient (A21) values for the S1 states of 200 conformations of CND1 (blue) and the simulated emission spectrum obtained from broadening the spectral lines with FWHM = 20 nm Gaussian functions (red). S 21

22 Figure S25. Top: Contour plot of the simulated luminescence decay. Bottom: Normalized simulated luminescence decay curves for wavelengths between 510 and 610 nm. S 22

23 Quenching Experiments with Emission Up-conversion Spectroscopy Figure S26. Left: Time-luminescence profiles of pcnds in the absence (black) and the presence of 0.1 M MV 2+ (red) at 460 nm obtained by fluorescence up-conversion. Right: Time-intensity profiles of pcnds in the absence (black) and the presence of 1 M TEOA (blue) at 460 nm obtained by fluorescence up-conversion. Figure S27. Top: Emission up-conversion spectra of pcnd with MV 2+ at time delays between 0 and 1000 ps upon excitation at 387 nm at room temperature. Time emission profiles of pcnd (black) and pcnd + MV 2+ (red) recorded at 440 nm. Figure S28. Left: Emission up-conversion spectra of pcnd with TEOA at time delays between 0 and 1000 ps upon excitation at 387 nm at room temperature. Right: Time emission profiles of pcnd + 1 M TEOA at 440, 460, and 480 nm. S 23

24 Steady State Quenching Figure S29. Steady-state luminescence quenching of pcnd with increasing amounts of MV 2+ upon 350 nm excitation Figure S30. Steady-state luminescence quenching of pcnd with increasing amounts of TEOA upon 350 nm excitation.. S 24

25 Figure S31. Normalized luminescence spectra of pcnd prior and after addition of 0.1 M MV 2+ upon excitation at 350 nm. Figure S32. Normalized luminescence spectra of pcnd prior and after addition of 1 M TEOA upon excitation at 350 nm. S 25

26 Lifetimes Table S2. Luminescence lifetimes of pcnds with different amounts of MV 2+ obtained by TCSPC fits at 450 nm (λex = 403 nm). τ1 [ns] τ2 [ns] τ3 [ns] pcnd % % % M MV % % M MV % Table S3. Lifetimes of pcnd with different amounts of MV 2+ obtained by transient absorption spectroscopy fit at 625 nm. τ1 [ps] τ2 [ps] τ3 [ps] pcnd M MV M MV M MV % 3.2 3% 74% % 13 3% 57% % 13 6% 52% % 8.8 9% Table S4: Lifetimes of pcnds with different amounts of TEOA obtained by TCSPC fit at 450nm (λex = 403 nm). τ1 [ns] τ2 [ns] τ3 [ns] pcnd % % % M TEOA % % % + 1 M TEOA % % Table S5. Lifetimes of pcnd with different amounts of TEOA obtained by transient absorption spectroscopy fit at 670 nm. τ1 [ps] τ2 [ps] pcnd % 3.1 1% τ3 [ps] M TEOA % % 37 13% M TEOA % % 34 29% + 1 M TEOA 1.0 7% % 43 48% Tab. S6. Luminescence lifetimes of pcnds in the absence and the presence of 1 M TEOA obtained by emission up-conversion at 460 nm (λex = 387nm). S 26

27 τ1 [ps] τ2 [ps] pcnd % % + 1 M TEOA % % Tab. S7. Luminescence lifetimes of pcnds in the absence and the presence of 0.1 M MV 2+ obtained by fluorescence up-conversion at 460 nm (λex = 387nm). τ1 [ps] τ2 [ps] pcnd % % M MV % % S 27