Supporting Information. Evaluating steady-state and time-resolved fluorescence as a tool to study the behavior of asphaltene in toluene

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1 Electronic Supplementary Material (ESI) for Photochemical & Photobiological Sciences. This journal is The Royal Society of Chemistry and Owner Societies 2014 Supporting Information Evaluating steady-state and time-resolved fluorescence as a tool to study the behavior of asphaltene in toluene Hui Ting Zhang, Rui Li, Zixin Yang, Cindy-Xing Yin, Murray R. Gray* and Cornelia Bohne*,, Department of Chemistry, University of Victoria, PO Box 3065, Victoria, BC, Canada V8W 3V6, Canada, Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 2G6, Canada Index Steady-state asphaltene emission spectra Fig. S1 Analysis of fluorescence decays Fig. S2 Table S1 Time-resolved experiments for the emission of asphaltene at 520 nm Table S2 Table S3 Average lifetimes for the emission of AA-5 Fig. S3 Fig. S4 Addition of pyrene as an external probe and quenching of excited pyrene with nitromethane Fig. S5 Table S4 Fig. S6 Fig. S7 Table S5 Absorption and fluorescence spectra for different asphaltene samples Fig. S8 Fig. S9 Average lifetimes for AA-5 in toluene/heptane mixtures Table S6 S2 S2 S3 S4 S5 S5 S6 S6 S6 S6 S7 S7 S7 S7 S8 S8 S 1

2 Steady-state asphaltene emission spectra. Figure S1. Fluorescence spectra for asphaltene (8 mg/l) in toluene excited at 310 nm (a, black), 335 nm (b, red), 350 nm (c, blue), 404 nm (d, green), 450 nm (e, black) and 500 nm (f, red). Analysis of fluorescence decays. The decays were fit to an increasing number of exponentials until adequate fits, based on χ 2 values and random residuals, were obtained. The fit of the emission decays to the sum of one or two exponentials was not adequate, while the fits to the sum of three or four exponentials were adequate (Fig. S2). The fits of the emission decay at 420 nm for asphaltene in toluene excited at 335 nm are shown in Table S1 for a sum of three or four exponentials. For the concentrations of 100 mg/l and 500 mg/l the fit to the sum of three exponentials was inadequate as indicated by the χ 2 values higher than 1.2. The whole data set was fit to the sum of four exponentials in order to make the comparison of the average lifetimes possible for different samples. Figure S2. Decay for the emission (λ ex = 335 nm; λ em = 420 nm) of 1 g/l of asphaltene in toluene (red) fit to the sum of four exponentials (blue). The IRF is shown in black. The residual plots for the fits of the data to a different number of exponentials are shown in panels a to d: a, four exponentials - χ 2 = 1.028; b, three exponentials - χ 2 = 1.126; c, two exponentials - χ 2 = 3.32 and d, one exponential - χ 2 = 51.1 S 2

3 Table S1. Recovered lifetimes (τ), pre-exponential factors (A), average lifetimes (<τ>) and χ 2 values for the emission of asphaltene in toluene at different concentrations (λ ex/em = 335/420 nm) fit to the sum of three or four exponentials. a, b [asphaltene] mg/l τ 1 / ns (A 1 ) τ 2 / ns (A 2 ) τ 3 / ns (A 3 ) τ 4 / ns (A 4 ) <τ> / ns χ c 0.86 ± 0.02 (0.71 ± 0.01) 0.1 c 0.33 ± 0.07 (0.41 ± 0.05) 0.5 c 0.82 ± 0.02 (0.69 ± 0.01) 0.5 c 0.33 ± 0.08 (0.40 ± 0.04) 1 c 0.83 ± 0.02 (0.70 ± 0.01) 1 c 0.4 ± 0.1 (0.35 ± 0.05) 10 c 0.78 ± 0.02 (0.69 ± 0.01) 10 c 0.48 ± 0.06 (0.49 ± 0.04) 50 d 0.61 ± 0.02 (0.68 ± 0.01) 50 d 0.30 ± 0.04 (0.56 ± 0.04) 100 d 0.63 ± 0.02 (0.69 ± 0.01) 100 d 0.18 ± 0.04 (0.7 ± 0.2) 500 d 0.57 ± 0.02 (0.68 ± 0.02) 500 d 0.22 ± 0.04 (0.61 ± 0.09) 1000 d 0.67 ± 0.02 (0.71 ± 0.01) 1000 d 0.23 ± 0.06 (0.5 ± 0.1) 3.02 ± 0.06 (0.26 ± 0.01) 1.24 ± 0.08 (0.43 ± 0.04) 2.82 ± ± 0.09 (0.42 ± 0.04) 2.86 ± 0.06 (0.25 ± 0.01) 1.1 ± 0.1 (0.45 ± 0.07) 2.72 ± ± 0.2 (0.36 ± 0.04) 2.40 ± ± 0.09 (0.32 ± 0.02) 2.45 ± ± 0.05 (0.26 ± 0.03) 2.42 ± ± 0.08 (0.27 ± 0.03) 2.60 ± 0.05 (0.25 ± 0.01) 1.07 ± 0.08 (0.33 ± 0.04) 9.0 ± 0.2 (0.029 ± 0.002) 3.7 ± 0.2 (0.14 ± 0.01) 8.5 ± 0.1 (0.042 ± 0.002) 3.5 ± 0.2 (0.15 ± 0.02) 8.5 ± 0.1 (0.042 ± 0.002) 3.3 ± 0.2 (0.18 ± 0.02) 8.2 ± 0.1 (0.041 ± 0.001) 3.9 ± 0.4 (0.13 ± 0.02) 7.82 ± 0.09 (0.052 ± 0.001) 3.6 ± 0.3 (0.11 ± 0.01) 7.95 ± 0.09 (0.039 ± 0.001) 3.8 ± 0.2 (0.08 ± 0.01) 7.85 ± 0.09 (0.049 ± 0.001) 3.3 ± 0.2 (0.11 ± 0.01) 8.0 ± 0.1 (0.040 ± 0.001) 3.2 ± 0.1 (0.13 ± 0.01) ± ± 0.4 (0.024 ± 0.003) 1.42 ± ± ± 0.3 (0.024 ± 0.003) 1.39 ± ± ± 0.3 (0.025 ± 0.003) 1.5 ± ± ± 0.5 (0.025 ± 0.005) 1.5 ± ± ± 0.3 (0.021 ± 0.003) 1.16 ± ± ± 0.4 (0.015 ± 0.002) 0.88 ± ± ± 0.2 (0.018 ± 0.002) 0.95 ± ± ± 0.2 (0.019 ± 0.003) 1.04 ± a, errors were obtained from the fit of the experimental decays to a sum of exponentials using the Edinburgh Instruments software. b, all experiments were performed once on the same day. c, experiments were performed using a 90-degree arrangement between the excitation source and the detection optics. d, experiments were performed with the front-face sample holder. S 3

4 Time-resolved experiments for the emission of asphaltene at 520 nm. The decays for the emission at 520 nm were collected using an excitation wavelength at 335 nm or 404 nm. Some decays could be fit to a sum of four exponentials, while some decays could only be fit to 3 exponentials. Attempts to fit these decays to the sum of four exponentials did not lead to the recovery of a fourth lifetime or led to two lifetimes with equal values. Fits using a sum of three exponentials were employed for the comparison of average lifetimes for different samples, since in all cases the χ 2 values and the distribution of residuals were acceptable. Table S2. Recovered lifetimes (τ), pre-exponential factors (A) and average lifetimes (<τ>) for asphaltene in toluene at different concentrations (λ ex/em = 335/520 nm). [asphaltene] mg/l ± 0.04 (4) a, b (0.55± 0.01) ± 0.04 (6) a, b (0.54 ± 0.01) ± 0.02 (2) a, c (0.57 ± 0.01) ± 0.04 (2) a, b (0.55 ± 0.02) ± 0.03 (2) a, c (0.54 ± 0.01) ± 0.03 (2) a, b (0.52 ± 0.01) ± 0.06 (2) a, c (0.53 ± 0.01) ± 0.05 (2) a, c (0.51 ± 0.02) ± 0.06 (2) a, c (0.50 ± 0.01) ± 0.05 (2) a, c (0.51 ± 0.02) ± 0.03 (4) a, c (0.50 ± 0.01) ± 0.06 (2) a, c (0.50 ± 0.01) ± 0.07 (2) a, c (0.50 ± 0.01) ± 0.06 (2) a, c (0.51 ± 0.01) τ 1 / ns (A 1 ) τ 2 / ns (A 2 ) τ 3 / ns (A 3 ) <τ> / ns 3.53 ± 0.09 (0.39 ± 0.01) 3.52 ± 0.08 (0.39 ± 0.01) 3.54 ± 0.08 (0.38 ± 0.02) 3.58 ± 0.09 (0.40 ± 0.01) 3.45 ± 0.06 (0.40 ± 0.01) 3.51 ± 0.08 (0.41 ± 0.01) 3.41 ± 0.08 (0.40 ± 0.02) 3.4 ± 0.1 (0.42 ± 0.02) 3.35 ± 0.09 (0.43 ± 0.01) 3.4 ± 0.1 (0.42 ± 0.01) 3.41 ± 0.03 (0.43 ± 0.01) 3.3 ± 0.1 (0.42 ± 0.01) 3.21 ± 0.07 (0.43 ± 0.01) 3.08 ± 0.09 (0.42 ± 0.01) 9.3 ± 0.2 (0.059 ± 0.009) 9.4 ± 0.2 (0.063 ± 0.006) 9.7 ± 0.2 (0.054 ± 0.002) 9.7 ± 0.2 (0.060 ± 0.006) 9.4 ± 0.2 (0.060 ± 0.005) 9.5 ± 0.2 (0.069 ± 0.005) 9.4 ± 0.2 (0.066 ± 0.009) 9.2 ± 0.2 (0.071 ± 0.001) 9.2 ± 0.2 (0.072 ± 0.004) 9.2 ± 0.2 (0.070 ± 0.006) 9.2 ± 0.1 (0.072 ± 0.003) 9.1 ± 0.2 (0.076 ± 0.006) 8.7 ± 0.1 (0.076 ± 0.006) 8.3 ± 0.2 (0.073 ± 0.005) 2.62 ± ± ± ± ± ± ± ± ± ± ± ± ± ± 0.04 a, values in parenthesis correspond to the number of independent experiments. Errors for the average of two independent experiments correspond to the average deviation or the propagation of individual error values, whichever is larger. b, experiments were performed using a 90-degree geometry between the excitation and emission optics. c, experiments were performed using the front-face sample holder. S 4

5 Table S3. Recovered lifetimes (τ), pre-exponential factors (A) and average lifetimes (<τ>) for asphaltene in toluene at different concentrations (λ ex/em = 404/520 nm). [asphaltene] mg/l ± 0.02 (3) a, b (0.60 ± 0.01) ± 0.04 (4) a, b (0.60 ± 0.02) ± 0.03 (2) a, b (0.60 ± 0.02) ± 0.04 (3) a, b (0.61 ± 0.01) ± 0.03 (3) a, c (0.61 ± 0.01) ± 0.03 (2) a, c (0.57 ± 0.01) ± 0.03 (2) a, c (0.58 ± 0.01) ± 0.08 (5) a, c (0.57 ± 0.02) ± 0.03 (2) a, c (0.54 ± 0.01) ± 0.1 (2) a, c (0.54 ± 0.01) ± 0.09 (4) a, c (0.59 ± 0.02) τ 1 / ns (A 1 ) τ 2 / ns (A 2 ) τ 3 / ns (A 3 ) <τ> / ns 3.51 ± 0.06 (0.35 ± 0.01) 3.5 ± 0.1 (0.35 ± 0.01) 3.5 ± 0.1 (0.35 ± 0.01) 3.50 ± 0.05 (0.35 ± 0.01) 3.50 ± 0.06 (0.34 ± 0.01) 3.43 ± 0.08 (0.37 ± 0.01) 3.53 ± 0.06 (0.36 ± 0.01) 3.4 ± 0.2 (0.38 ± 0.01) 3.29 ± 0.06 (0.39 ± 0.01) 3.2 ± 0.1 (0.39 ± 0.01) 3.1 ± 0.1 (0.35 ± 0.02) 9.5 ± 0.2 (0.051 ± 0.005) 9.4 ± 0.2 (0.050 ± 0.004) 9.5 ± 0.3 (0.050 ± 0.006) 9.4 ± 0.1 (0.051 ± 0.003) 9.3 ± 0.1 (0.052 ± 0.002) 9.3 ± 0.2 (0.057 ± 0.005) 9.4 ± 0.1 (0.059 ± 0.003) 9.1 ± 0.3 (0.059 ± 0.004) 8.9 ± 0.2 (0.064 ± 0.005) 8.6 ± 0.2 (0.065 ± 0.003) 8.2 ± 0.1 (0.057 ± 0.005) 2.46 ± ± ± ± ± ± ± ± ± ± ± 0.08 a, values in parenthesis correspond to the number of independent experiments. Errors for the average of two independent experiments correspond to the average deviation or the propagation of individual error values, whichever is larger. Errors for more than two independent experiments correspond to the standard deviation. b, experiments were performed using a 90-degree geometry between the excitation and emission optics. c, experiments were performed using the front-face sample holder. Average lifetimes for the emission of AA-5. At very low absorbencies at the excitation wavelengths only the sample holder with a 90-degree geometry between the excitation and emission optics can be used. At moderate concentrations (10-50 mg/l) both samples holders were used and a shortening by ca. 0.2 ns was observed for the average lifetimes measured using the front-face sample holder (Fig. S3). However, the trends for the lifetimes remained the same. Figure S3. Dependence with the asphaltene concentration of the average lifetimes for the asphaltene emission at 420 nm in toluene when excited at 335 nm. The circles (red) correspond to measurements using a sample holder with a 90-degree arrangement between the excitation and detection optics while the squares (blue) correspond to measurements using the front-face sample holder. The dashed lines correspond to the lower limit of the error bar for the measurement with each sample holder at the lowest asphaltene concentration measured. S 5

6 The average lifetimes for the emission at 520 nm when the samples were excited at 404 nm were shorter than the lifetimes when the sample was excited at 335 nm (Fig. S4). Figure S4. Dependence with the asphaltene concentration of the average lifetimes for the asphaltene emission at 520 nm when excited at 335 nm (open symbols) or at 404 nm (closed symbols). Addition of pyrene as an external probe and quenching of excited pyrene with nitromethane. The emission spectra of pyrene and asphaltene overlap. At low asphaltene concentrations ( 2 mg/l) the emission from asphaltene was subtracted from the total emission (Fig. S5 top). The emission intensity for pyrene decreased but the shape of the spectra did not change. The relative contribution of the asphaltene emission was much larger at the higher asphaltene concentrations (Fig. S5 bottom) where the pyrene emission appears as a fine structure superimposed to the asphaltene emission. Figure S5. Top: Emission of pyrene in toluene (20 µm, λ ex = 337 nm) in the presence of asphaltene (a: 0, b: 1 mg/l, c: 2 mg/l) where the emission of asphaltene was subtracted from the total spectrum. Bottom: Normalized fluorescence emission of solutions containing pyrene (20 µm, λ ex = 337 nm) and asphaltene (d: 0, e: 10 mg/l, f: 50 mg/l, g: 100 mg/l). Table S4. Lifetime for the pyrene (20 µm, λ ex = 335 nm, λ em = 391 nm) singlet-excited state in toluene in the absence and presence of asphaltene. a asphaltene / mg/l τ / ns 0 (6) b, c 305 ± 9 10 (2) b, c 306 ± (3) b, d 276 ± (2) b, d 186 ± (2) b, d 121 ± 1 a, errors for the average of two independent experiments correspond to the average deviation. Errors for more than two experiments correspond to standard deviations. b, values in parenthesis correspond to the number of independent experiments. c, experiments performed with a 90-degree arrangement between the excitation and emission optics. d, experiments performed with the front-face sample holder. The quenching of the singlet-excited state of pyrene by asphaltene is responsible for the shortening of the pyrene lifetime (Table S4). The average molecular weight for asphaltene was assumed to be 750 g/l. The quenching plot is linear (Fig. S6) with a S 6

7 recovered quenching rate constant of (3.7 ± 0.2) 10 9 M -1 s -1. Figure S6. Quenching plot for pyrene (20 µm) in toluene by asphaltene. The observed rate constants correspond to the longest lifetime recovered from the pyrene/asphaltene solutions. Nitromethane quenches the singlet-excited state of pyrene leading to faster decays at higher nitromethane concentrations. The quenching plots in the absence of asphaltene and at all the asphaltene concentrations studied were linear (Fig. S7). The average quenching rate constants are shown in Table S5. Table S5. Quenching rate constants (k q ) for the quenching of the singlet excited-state of pyrene (20 µm, λ ex = 335 nm, λ em = 391 nm) in toluene by nitromethane at various nitromethane concentrations. [asphaltene] / k q /10 9 M -1 s -1 mg/l 0 (5) a, b 3.2 ± (1) a, b 3.3 ± (3) a, c 3.5 ± (2) a, c 3.6 ± (1) a, c 3.8 ± 0.2 a, values in parenthesis correspond to the number of independent experiments. Errors for the average of two independent experiments correspond to the average deviation or to the propagation of individual error values, whichever is larger. Errors for more than two independent experiments correspond to the standard deviation. Errors for one independent experiment were estimated to be ± 0.2. b, experiments using a 90-degree arrangement between the excitation/emission optics. c, experiments using the frontface sample holder. Absorption and fluorescence spectra for different asphaltene samples. Figure S7. Quenching plots for the quenching of pyrene (20 µm, λ ex = 335 nm, λ em = 391 nm) by nitromethane in the presence of various asphaltene concentrations: 0 (O, red), 10 mg/l (, blue), 100 mg/l, (, green), 500 mg/l (, black) and 1 g/l (, purple). Figure S8. Absorption spectra for 10 mg/l solutions in toluene of: AA-5 (black), AA-7 (a, blue), CL-5 (red), CL-7 (green), TC-AA-5 (purple) and TC-AA-7 (orange). S 7

8 Figure S9. Normalized steady-state emission spectra for the emission of 10 mg/l asphaltene solutions in toluene when excited at 335 nm: TC-AA-5 (a, blue), AA-5 (b, black), TC-CL5 (c, green) and CL-5 (d, red). Average lifetimes for AA-5 in toluene/heptane mixtures. Table S6. Average lifetimes for the emission at 420 nm (λ ex = 335 nm) of AA-5 (100 mg/l) in tolueneheptane solutions. V TL / <τ> / ns % 0.5 h 2 days 6 days 9 days ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 0.1 a 1.0 ± 0.1 a 1.3 ± 0.1 a ± ± 0.1 a 1.2 ± 0.1 a 1.4 ± 0.1 a ± 0.1 a 1.2 ± 0.1 a 1.2 ± 0.1 a 1.4 ± 0.1 a a, these samples contained precipitated material. The lifetimes were determined for the supernatant. S 8