Supporting Information. Shining New Light on the Spiropyran Photoswitch: A Photocage Decides between cis-trans or Spiro-Merocyanine Isomerization.

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1 Supporting Information Shining New Light on the Spiropyran Photoswitch: A Photocage Decides between cis-trans or Spiro-Merocyanine Isomerization. Cassandra L. Fleming, Shiming Li, Morten Grøtli, and Joakim Andréasson*, Addresses Department of Chemistry and Molecular Biology, University of Gothenburg, SE-41296, Göteborg, Sweden Department of Chemistry and Chemical Engineering, Chemistry and Biochemistry, Chalmers University of Technology, SE-41296, Göteborg, Sweden Table of contents S2. Synthesis S2. General Methods and Materials S2 S4. Synthesis of c-model and 1c-trans-MC S4. Synthesis of 2Me-trans-MC S5. Synthesis of 3Me-trans-MC S5. Synthesis of SPMe-6H S6 S11. 1 H, 13 C NMR spectra and HRMS spectra of compounds c-model, 1c-trans-MC, 2Metrans-MC, 3Me-trans-MC and SPMe-6H S12. Spectroscopic Measurements and Photophysics S12. Merocyanine isomers S13. UV/vis absorption spectra of compound 1 S14 S16. UV/vis absorption spectra of the model compounds S17 S18. Photocycling S18. Decaging mechanism for 1c-trans-MC S19 S23. NMR spectra before and after irradiation of 1c-trans-MC (vis), 2Me-trans-MC (vis), 3Me-trans-MC (vis) and 1SP (UV) S23. NMR spectra of SPMe-6H after acidification with CF3SO3H S24. References S1

2 Synthesis General Methods and Materials All 1 H NMR (400 MHz), 13 C NMR (101 MHz) and 2D NMR (ghmbc, ghsqc) spectra were recorded on Varian Unity 400 spectrometer at 25 C. In the 1 H and 13 C NMR spectra, chemical shifts ( /ppm) were referenced to the residual solvent peak specific to that of the deuterated solvents; DMSO-d6: 2.50 ppm ( 1 H NMR) and ppm ( 13 C NMR), MeOH-d4: 3.10 ( 1 H NMR), MeCN-d3: 1.94 ppm ( 1 H NMR). HRMS was obtained using Agilent 1290 Infinity LC system tandem to an Agilent 6520 accurate mass Q-TOF LC/MS with an APCI source in a positive mode. Thin-layer chromatography was performed on silica gel plates (Merck Kieselgel 60, F254) to monitor the reactions. Spots were made visible with UV light. All general reagents and solvents were purchased from commercial sources and used as supplied without further purification, unless stated otherwise. Acetonitrile (MeCN) was distilled over CaH2. Experimental procedures for the synthesis of compounds Synthesis of c-model and 1c-trans-MC Scheme S1. Reagents and conditions: (a) Cs2CO3, MeCN, 80 C, 3 h, Ar; (b) CH3COONa, (CH3CO)2O, 80 C, 45 min, Ar. S2

3 To 2-hydroxy-5-nitrobenzaldehyde (2.34 g, 14 mmol) and 1-(bromomethyl)-2-nitrobenzene (3.02 g, 14 mmol) was added distilled MeCN (70 ml) under argon. Cesium carbonate (2.00 g, 6.1 mmol) was added and the mixture was heated at 80 C for 3 h with stirring under argon. After cooling to room temperature, the resulting light yellow solid was collected, washed with MeCN, and then suspended in water (100 ml) with stirring for 1 h. The grey white solid, c-model was collected and dried (3.35 g, yield 79%). 1 H NMR (400 MHz, DMSO-d6) δ (s, 1H; CHO), (m, 2H; H-4, H-6), 8.19 (ddd, J = 8.2, 1.3, 0.3 Hz, 1H; H-10), 7.97 (ddd, J = 7.8, 1.5, 0.5 Hz, 1H; H-13), 7.84 (td, J = 7.6, 1.3 Hz, 1H; H-12), 7.67 (ddd, J = 8.1, 7.4, 1.4 Hz, 1H; H-11), (m, 1H, H-3), 5.82 (s, 2H; H-7). 13 C NMR (101 MHz, DMSO-d6) δ (CHO), (C-2), (C-9), (C-5), (C-12), (C-8), (C-4), (C-11), (C-13), (C-10), (C-1), (C-6), (C-3), 68.1 (C-7). To a mixture of 5-nitro-2-((2-nitrobenzyl)oxy)benzaldehyde (c-model) 1,2,3,3- tetramethylindolenium iodide (301 mg, 1.0 mmol) and anhydrous sodium acetate (82 mg, 1.0 mmol) was added acetic anhydride (6 ml) under argon. The reaction mixture was stirred at 80 C for 45 min. After cooling to room temperature, the resulting red solid was collected by filtration, washed with water and Et2O, dried under vacuum to afford 1c-trans-MC (424 mg, yield 74%). 1 H NMR (400 MHz, DMSO-d6) δ 9.14 (d, J = 2.8 Hz, 1H; H-13), 8.47 (dd, J = 9.2, 2.8 Hz, 1H; H-15), 8.38 (d, J = 16.6 Hz, 1H; H-11), 8.21 (dd, J = 8.1, 1.1 Hz, 1H; H-21), (m, 4H; H-4, H-7, H-23, H-24), 7.89 (d, J = 16.6 Hz, 1H; H-10), (m, 1H; H-22), (m, 2H; H-5, H-6), 7.59 (d, J = 9.3 Hz, 1H; H-16), 5.84 (s, 2H; H-18), 4.06 (s, 3H; NCH3), 1.70 (s, 6H; C(CH3)2). 13 C NMR (101 MHz, DMSO-d6) δ (C-2), (C-17), (C-20), (C-11), (C-8), (C-9), (C-14), (C-23), (C-22), (C-19), (C-24), S3

4 129.8 (C-6), (C15), (C-5), (C-13), (C-21), (C-12), (C-4), (C-10), (C-7), (C-16), 68.5 (C-18), 52.3 (C-3), 34.8 (NCH3), (C(CH3)2). HRMS (ESI, m/z): found [M - I] + = ; calcd for [M - I] + (C26H24N3O5) = Synthesis of 2Me-trans-MC Scheme S2. Reagents and conditions: (a) K2CO3, DMF, rt, 12 h; (b) CH3COONa, (CH3CO)2O, 80 C, 45 min, Ar. To a mixture of 2-methoxy-5-nitrobenzaldehyde [1] (181 mg, 1.0 mmol), 1,2,3,3- tetramethylindolenium iodide (301 mg, 1 mmol) and anhydrous sodium acetate (82 mg, 1.0 mmol) was added acetic anhydride (3 ml) under argon. The reaction mixture was stirred at 80 C for 45 min. After cooling to room temperature, the resulting orange solid was collected by filtration, washed with water and Et2O, dried under vacuum to afford 2Me-trans-MC (387 mg, yield 83%). 1 H NMR (400 MHz, DMSO-d6) δ 9.10 (d, J = 2.8 Hz, 1H; H-13), 8.47 (dd, J = 9.3, 2.8 Hz, 1H; H-15), 8.41 (d, J = 16.6 Hz, 1H; H-11), (m, 2H; H-4, H-7) 7.93 (d, J = 16.6 Hz, 1H; H- 10), (m, 2H; H-5, H-6), 7.48 (d, J = 9.3 Hz, 1H; H-16), 4.18 (s, 3H; NCH3), 4.16 (s, 3H; OCH3), 1.78 (s, 6H; C(CH3)2). 13 C NMR (101 MHz, DMSO-d6) δ (C-2), (C-17), (C-11), (C-8), (C-9), (C-14), (C-5), (C-15), (C-6), (C-13), (C-4), (C- 12), (C-7), (C-10), (C-16), 57.7 (C-17), 52.3 (C-3), 34.9 (NCH3), 25.3 (C(CH3)2. HRMS (Q-TOF, ESI, m/z): found [M - I] + = ; calcd for [M - I] + (C20H21N2O3) = S4

5 Synthesis of 3Me-trans-MC Scheme S3. Reagents and conditions: (a) CH3COONa, (CH3CO)2O, 80 C, 45 min, Ar. To a mixture of 2-methoxybenzaldehyde (408 mg, 3.0 mmol), 1,2,3,3-tetramethylindolenium iodide (904 mg, 3.0 mmol) and anhydrous sodium acetate (246 mg, 3.0 mmol) was added acetic anhydride (7 ml) under argon. The reaction mixture was stirred at 80 C for 45 min. After cooling to room temperature, the resulting orange solid was collected by filtration, washed with water and Et2O, dried under vacuum to afford 3Me-trans-MC (1.16 g, yield 93%). 1 H NMR (400 MHz, DMSO-d6) δ 8.48 (d, J = 16.5 Hz, 1H; H-11), 8.24 (dd, J = 8.0, 1.6 Hz, 1H; H-13), (m, 2H; H-4, H-7), 7.73 (d, J = 16.5 Hz, 1H; H-10), (m, 3H; H-5, H- 6, H-15), 7.25 (dd, J = 8.6, 1.0 Hz, 1H; H-16), 7.17 (td, J = 7.5, 1.0 Hz, 1H; H-14), 4.14 (s, 3H; NCH3), 4.01 (s, 3H; OCH3), 1.77 (s, 6H; C(CH3)2). 13 C NMR (101 MHz, DMSO-d6) δ (C-2), (C-17), (C-11), (C-8/C-9), (C-8/C9), (C-14), (C-13), (C-5/C-6), (C-5/C-6), (C-12), (C-4), (C-15), (C-7), (C-10), (C-16), 56.4 (OCH3), 52.0 (C-3), 34.6 (NCH3), 25.8 (C(CH3)2). Synthesis of SPMe-6H SPMe-6H was synthesized according to the procedure of reference. [2] The 1 H NMR data (see Figure S11) is in agreement with published data. [2] S5

6 1 H, 13 C NMR and HRMS of compounds c-model, 1c-trans-MC, 2Me-trans-MC, 3Me-trans-MC and SPMe-6H Figure S1. 1 H NMR (400 MHz, DMSO-d6) of compound c-model. Figure S2. 13 C NMR (101 MHz, DMSO-d6) of compound c-model. S6

7 Figure S3. 1 H NMR (400 MHz, DMSO-d6) of compound 1c-trans-MC. Figure S4. 13 C NMR (101 MHz, DMSO-d6) of compound 1c-trans-MC. S7

8 Figure S5. HRMS of compound 1c-trans-MC. Figure S6. 1 H NMR (400 MHz, DMSO-d6) of compound 2Me-trans-MC. S8

9 Figure S7. 13 C NMR (101 MHz, DMSO-d6) of compound 2Me-trans-MC. Figure S8. HRMS of compound 2Me-trans-MC. S9

10 Figure S9. 1 H NMR (400 MHz, DMSO-d6) of compound 3Me-trans-MC. Figure S C NMR (101 MHz, DMSO-d6) of compound 3Me-trans-MC. S10

11 Figure S11. 1 H NMR (400 MHz, MeCN-d3) of compound SPMe-6H. S11

12 Spectroscopic Measurements and Photophysics All UV/vis absorption and fluorescence experiments were performed in ethanol solution (99.7%). Deoxygenation of the samples was not performed. Ground state absorption spectra were recorded on a Varian Cary 4 Bio UV/vis spectrophotometer with baseline correction. Corrected fluorescence spectra were recorded on a SPEX Fluorolog-3 spectrofluorometer. The photoinduced reactions (decaging and isomerization) were performed in the UV at 254 nm and 302 nm using UVP lamp models UVGL-25 (254 nm, 700 µw/cm 2 at the sample) or UVM-57 (302 nm, 1.5 mw/cm 2 at the sample), respectively, and in the visible at 405 nm (LED Engin LZ1 10UB00-00U8, ca. 50 mw/cm 2 at the sample) or at 523 nm (LED Engin LZ1-10G100, ca. 25 mw/cm 2 at the sample). Irradiation conditions are detailed in Figure S13. Merocyanine isomers Figure S12. The merocyanine open isomer exists as eight different forms, as,, and can adopt either cis (C) or trans (T) geometry. Note that any XCX geometry are referred to as cis, and that any XTX geometry is referred to as trans. Depicted in the Figure is the TTC form. S12

13 UV/vis absorption spectra of compound Absorbance Wavelength (nm) Figure S13. Absorption spectra of 1c-trans-MC before irradiation (black line) and after irradiation at 405 nm ( 50 mw/cm 2 ) for 4 seconds to generate 1c-cis-MC (green line). Subsequent irradiation at 302 nm ( 1.5 mw/cm 2 ) for 5 seconds yields a PSD enriched to ca. 60% of 1c-trans-MC (blue line). Exposure to 5 cycles of alternating 302 nm and 405 nm light yielded the magenta line after thermal equilibrium establishment. Decaging with 254 nm UV (700 µw/cm 2 ) for 4 minutes results in the formation of 1MC, evidenced by the absorption band at 541 nm (red line). Note that Et3N (1 µl) was added followed by additional irradiation at 302 nm prior to recording the 1MC spectrum. All spectra in ethanol solution at a total concentration of M. S13

14 UV/vis absorption spectra of the model compounds Before irradiation PSD (405 nm) PSD (302 nm) Absorbance Wavelength (nm) Figure S14. Absorption spectra of 2Me-trans-MC before irradiation (black line) and after irradiation at 405 nm to generate 2Me-cis-MC (red line). Subsequent irradiation at 302 nm yields a PSD enriched to ca. 60% of 2Me-trans-MC (blue line). All spectra in ethanol solution at a total concentration of M. S14

15 Absorbance Wavelength (nm) Figure S15. Absorption spectra of 1SP as synthesized (black line), 1MCH (red line), and 1MC (blue line). 1MCH was prepared by UV exposure and subsequent acidification of 1SP by adding 1.2 equivalent of acid (TFA). The spectrum was recorded at thermal equilibrium, and thus represents virtually 100% 1MCH. 1MC was prepared by subsequent addition of 1.2 equivalent base (trimethylamine), and represents 100% 1MC. All spectra in ethanol solution at a total concentration of M. S15

16 Figure S16. Absorption spectrum of the model photocage (c-model) in ethanol solution before irradiation. S16

17 Photocycling 0.6 Absorbance Wavelength (nm) Figure S17. Photocycling of 1c-trans-MC using alternating 405 nm (green lines) and 302 nm (blue lines) exposure. The spectrum before irradiation is shown in red. All spectra in ethanol solution at a total concentration of M. S17

18 Absorbance Wavelength (nm) Figure S18. 1SP-1MC photocycling of 1c-trans-MC subsequent to decaging with 254 nm UV. Blue lines: After 302 nm exposure. Red lines: After 523 nm exposure. Decaging mechanism for 1c-trans-MC Figure S19: Decaging mechanism for 1c-trans-MC S18

19 NMR spectra before and after light-irradiation of 1c-trans-MC (vis), 2Me-trans-MC (vis), 3Metrans-MC (vis) and 1SP (UV) Figure S20. 1 H NMR of compound 1c-trans-MC in MeOH-d4. A: before irradiation. B: after visible light irradiation for 1.5 min (trans/cis = 53/47). Note that the distribution trans/cis after light irradiation does not reflect the photostationary distribution due to thermal isomerization cis trans on the same timescale as the data collection. Table S1. 1 H NMR (400 MHz, MeOH-d4) of 1c-trans-MC and 1c-cis-MC. 1c-trans-MC 1c-cis-MC H , d, J = 2.8 Hz H-13 Between H dd, J = 9.2, 2.8 Hz H , dd, J = 9.2, 2.8 Hz H , d, J = 9.2 Hz H , d, J = 9.2 Hz H , d, J = 16.8 Hz H-11 Between H , d, J = 16.8 Hz H , dq, J = 12.8, 1.2 Hz OCH2 5.82, s OCH2 5.70, s NCH3 4.12, s NCH3 3.52, d, J = 1.2 Hz C(CH3)2 1.76, s C(CH3)2 1.76, s H-4, H-5, H-6, H-7, H-21, H- 22, H-23, H , m H-4, H-5, H-6, H-7, H-21, H- 22, H-23, H , m S19

20 Figure S21. 1 H NMR of compound 2Me-trans-MC in MeOH-d4. A: before irradiation. B: after visible light irradiation for 1 min (trans/cis = 45/55). Note that the distribution trans/cis after light irradiation does not reflect the photostationary distribution due to thermal isomerization cis trans on the same timescale as the data collection. Table S2. 1 H NMR (400 MHz, MeOH-d4) of 2Me-trans-MC and 2Me-cis-MC. 2Me-trans-MC 2Me-cis-MC H , d, J = 2.8 Hz H , d, J = 2.8, 0.4 Hz H , dd, J = 9.6, 2.8 Hz H , dd, J = 9.2, 2.8 Hz H , d, J = 9.2 Hz H , d, J = 9.2 Hz H , d, J = 16.4 Hz H-11 Between H , d, J = 16.4 Hz H , dq, J = 13.2, 1.2 Hz OCH3 4.19, s OCH3 3.81, s NCH3 4.23, s NCH3 3.49, d, J = 1.2 Hz C(CH3) 1.85, s C(CH3) 1.77, s H-4, H-5, H-6, H , m H-4, H-5, H-6, H , m S20

21 Figure S22. 1 H NMR of compound 3Me-trans-MC in MeOH-d4. A: before irradiation. B: after visible light irradiation for 5 min (trans/cis = 58/42). Note that the distribution trans/cis after light irradiation does not reflect the photostationary distribution due to thermal isomerization cis trans on the same timescale as the data collection. S21

22 Figure S23. 1 H NMR of compound 1SP in MeOH-d4. Figure S24. 1 H NMR of compounds 1SP+1MC in MeOH-d4 (UV 365 nm, irradiation for 30 min). S22

23 Figure S25. 1 H NMR of compound 1SP (bottom panel) and 1SP+1MC (top panel, UV 365 nm, irradiation for 30 min) in MeOH-d4. Figure S26. 1 H NMR (400 MHz, MeCN-d3) of compound SPMe-6H after acidification with CF3SO3H (c.f. reference 2). S23

24 References [1] Jyothish, K.; Zhang, W. Angew. Chem. Int. Ed. 2011, 50, [2] Kortekaas, L.; Chen, J.; Jacquemin, D., Browne, W. R. J. Phys. Chem. B, 2018, 122, S24

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