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The Journal of Organic Chemistry
Data of optical spectroscopy: determination of pure spectra of all
4 EXPERIMENTAL SECTION
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particular isomers of compound 3, thermal reaction rates and sta-
bility, calculation of photoreaction as well as fluorescence quantum
yields
Synthesis of photoacid 3. Scheme 2 shows the synthetic route.
2,3,3-trimethylindoline 4 (3.00 g, 18.84 mmol, 1.0 eq) and 1,3-pro-
pan sultone (2.30 g, 18.84 mmol, 1.0 eq) were stirred at 120 °C for
1.5 h. Methanol was added to the reaction mixture and stirred at
room temperature for 30 min. Ethyl acetate and cyclohexane were
added. The white precipitate was filtered and washed with ethyl
acetate. The solid was dried under reduced pressure to afford 3-
(2,3,3-trimethyl-3H-indol-1-ium-1-yl)propane-1-sulfonate 5 (4.25
g, 15.12 mmol, 80%) as a white solid. 1H-NMR (500 MHz, DMSO-
d6): δ = 8.06-8.04 (m, 1H), 7.83-7.81 (m, 1H), 7.65-7.59 (m, 2H),
4.65 (t, J = 8.0 Hz, 2H), 3.51 (bs, 1H), 2.83 (s, 3H), 2.62 (t, J = 6.6
Hz, 2H), 2.18-2.12 (m, 2H), 1.53 (s, 6H) ppm. 13C-NMR (125
MHz, DMSO-d6): δ = 196.5, 141.9, 141.2, 129.3, 129.0, 123.4,
115.5, 54.1, 47.4, 46.6, 23.8, 22.1, 13.8 ppm. ESI-MS (+): m/z =
282.20 [M+H]+. HRMS: m/z calcd. for C14H20NO3S 282.11584
[M+H]+ found 282.11627 (Δm = 0.00043, error 1.5 ppm).
Simulated data: calculations of maximum obtainable pH jumps in
dependence of the particular pKa as well as starting pH values for
different sample concentrations.
AUTHOR INFORMATION
Corresponding Author
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ORCID
Alexander Heckel: 0000-0003-3541-4548
Josef Wachtveitl: 0000-0002-8496-8240
3-(2,3,3-Trimethyl-3H-indol-1-ium-1-yl)propane-1-sulfonate
(2.00 g, 7.11 mmol, 1.0 eq) was dissolved in EtOH (20 mL) and 3-
hydroxy-6-methylpicolinaldehyde 3 (0.98 g, 7.11 mmol, 1.0 eq)
were added. The reaction mixture was stirred at 80 °C for 8 h. The
precipitate was filtered and dried under reduced pressure to afford
3-(3,3,6‘-trimethylspiro[indoline-2,2‘-pyrano[3,2-b]pyridin]-1-
yl)propane-1-sulfonic acid (2.37 g, 5.92 mmol, 83%) as light red
solid. 1H-NMR: (500 MHz, DMSO-d6): δ = 8.48 (d, J = 15.8 Hz,
1H), 8.12-8.10 (m, 1H), 7.92 (d, J = 15.9 Hz, 1H), 7.89-7.88 (m,
1H), 7.67-7.63 (m, 2H), 7.40-7.36 (m, 2H), 4.75 (t, J = 7.7 Hz, 2H),
2.65 (t, J = 6.9 Hz, 2H), 2.51 (s, 3H), 2.23-2.17 (m, 2H), 1.77 (s,
6H) ppm. 13C-NMR: (125 MHz, DMSO-d6): δ = 181.6, 154.9,
150.0, 145.5, 143.6, 141.1, 136.6, 129.6, 129.2, 129.1, 126.0,
123.0, 115.6, 112.8, 52.3, 47.7, 46.3, 26.0, 24.7, 23.1 ppm. ESI-MS
(+): 401.20 [M+H]+. HRMS: m/z calcd. for C21H25N2O4S
401.15295 [M+H]+ found 401.15290 (Δm = 0.00005, error 0.1
ppm). Mp: 200 °C (dec).
Author Contributions
§ these authors have contributed equally
Notes
The authors declare no competing financial interests.
ACKNOWLEDGMENT
We thank the Deutsche Forschungsgemeinschaft (DFG) for fund-
ing through SFB 902 “Molecular Principles of RNA-based Regu-
lation”.
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NMR spectra. For the characterization of the compounds were
recorded on Bruker AVIII-HD 500 MHz instruments equipped
with a N2 cooled cryogenic probe head using d6-DMSO as solvent.
HRMS spectra were recorded using a Thermo Scientific MALDI
LTQ Orbitrap (see Supporting Information).
Photometric Measurements. The photometric studies with
compound 3 were performed either with a Jena Analytik Specord
S600 spectrometer or an Ocean Optics DH-mini UV-VIS-NIR light
source with an USB 4000 fiber spectrometer. For photoswitching
experiments the spectrophotometers were equipped with modular
ThorLabs cuvette holders and mounted LEDs with the wavelengths
340 nm, 420 nm and 530 nm.
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pH Measurements. The pH value of the sample solutions was
measured with a Mettler Toledo InLab Nano pH electrode. The
light-induced pH regulation experiments were performed in
0.01xPBS buffer by use of the above described spectrometers with
ThorLabs LEDs attached.
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ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the ACS
Publications website.
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15726–15734.
Özçoban, C.; Halbritter, T.; Steinwand, S.; Herzig, L.-M.;
Kohl-Landgraf, J.; Askari, N.; Groher, F.; Fürtig, B.;
1H and 13C NMR spectra of compounds 5 and 3
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