Isatin phenylhydrazones: Anion enhanced photochromic behaviour

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1 Electronic Supplementary Material (ESI) for Photochemical & Photobiological Sciences. This journal is The Royal Society of Chemistry and Owner Societies 2015 Electronic Supplementary Information (ESI) Isatin phenylhydrazones: Anion enhanced photochromic behaviour Marek Cigáň a, *, Klaudia Jakusová a, Martin Gáplovský b, Juraj Filo a, Jana Donovalová a, Anton Gáplovský a a Faculty of Natural Sciences, Institute of Chemistry, Comenius University, Mlynská dolina CH-2, SK Bratislava, Slovakia; s: (M.C.); (K.J.); (J.D.); (M.H.); (R.S.); (A.G.) b Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Comenius University, Odbojárov 10, SK Bratislava, Slovakia; (M.G.) * 1

2 EXPERIMENTAL SECTION Supporting information Synthesis General Scheme: Synthesis of 1 and 2 Z-isomers in EtOH. (E)-isatin N 2 -phenylhydrazones 1 and 2: (Z)-3-(phenylhydrazono)indolin-2-one Z1: Obtained from phenylhydrazine (0.76g) in 78% yield (1.24g), 1 H NMR (300 MHz, DMSO-d 6 ), δ: (s, 1H), (s, 1H), 7.56 (d, J = 7.5 Hz, 1H), (m, 4H), 7.25 (td, J = 7.7, 1.2 Hz, 1H), 7.05 (m, 2H), 6.93 (d, J = 7.8 Hz, 1H). 13 C NMR (75 MHz, CDCl 3 ) δ (s), (s), (s), (s), (s), (s), (s), (s), (s), (s), (s), (s). Anal. Calcd. for C 14 H 11 N 3 O (237.26) C, 70.87; H, 4.867; N, Found C, 71.71; H, 4.71; N, (Z)-3-(phenylhydrazono)-1-methylindolin-2-one Z2: Obtained from phenylhydrazine (0.69g) in 83% yield (1.30g), 1 H NMR (300 MHz, (CD 3 ) 2 CO), δ: (s, 1H), 7.63 (dd, J = 7.5, 0.5 Hz, 1H), (m, 5H), 7.13 (ddd, J = 7.6, 0.9 Hz, 1H), (m, 2H), 3.32 (s, 3H). 13 C NMR (75 MHz, DMSO), δ: (s), (s), (s), (s), (s), (s), (s), (s), (s), (s), (s), (s), (s). Anal. Calcd. for C 15 H 13 N 3 O (251.28) C, 71.70; H, 5.21; N, Found C, 71.82; H, 5.18; N,

3 Titration experiments Apparent association constant K ass determinations Equation (1) was rewritten to the following form for nonlinear fit: A = A0 + c1 *(P1- A0 ) * ( c0 + x +1/P2 - ( c0 + x +1/P2)^2-4 * c0 * x ), (2) where: c 0 = , c 1 = 1/2c 0 = , parameter P1 = A lim, parameter P2 = K ass and x = c A-. The A 0 value was fixed to the absorbance value A for x = 0. The large difference in constants c 0, c 1 and the x- data range led rescaling the nonlinear function (x and fitted parameter 1/P2 by a factor of 10 4 ). Following this modification, the standard non-linear least-squares Nelder-Mead minimization method was employed to determine fitting parameters P1 and P2. 60,61 Three different wavelengths were used to K ass determination of Z1 and Z2 (470 nm, 475 nm and 480 nm). 3

4 Light initiated E-Z and Z-E isomerization Quantum yield determination The Z-E isomerization quantum yield ( E-Z ) of isatin phenylhydrazone Z-isomers Z1 and Z2 in DMF solution was determined by equations (6) and (7) at low Z-E conversion (to eliminate the effect of back E-Z photoisomerization): 62 φ Z E = c t c 0 dc t I a dt 0 = Δc t I a dt 0 c = A λ ε (6); Z λ (7) where: c is the concentration change in Z-isomer, I a is Z-isomer absorbed photon flux at the irradiation wavelength using a monochromatic light source, A is the absorbance change at irradiation wavelength using a monochromatic light source, Z is Z-isomer molar extinction coefficient at irradiation wavelength using a monochromatic light source and t is irradiation time. Because only Z- isomers were isolated from the reaction mixture, the Z-isomer extinction coefficient at 405 nm was determined by Eq. (8): ε Z 405 = A 405 c Z. (8) The Z-isomer absorbed photon flux I a during Z-E isomerization at irradiation wavelength = 405 nm and incident Z-isomer concentration c 0 was calculated by Eq. (9): 62 I a,z 405 = I 0[ 1 10 [ε Z 405 (c 0 Δc)] ]. (9) The incident photon flux I 0 was determined by 2-nitrobenzaldehyde (2-NB) as chemical actinometer, according to Eq. (10): 63 k I 0 = 2.303ε o NB 405 φ o NB 405 l, (10) where: o-nb405 is the molar extinction coefficient of 2-NB at irradiation wavelength 405 nm, o-nb405 is the quantum yield of 2-NB photodegradation at irradiation wavelength, l is the path length and k is the 2- NB first-order photodegradation slope plotted under low-light-absorbing conditions: 63 4

5 (11) ln( [o NB] ) t = kt [o NB] 0. Quantum yield of the A-form transformation (Ф A ) induced by light (465 nm LED sources) was determined by Eqs. (12)-(14): (13) φ A = c t c 0 dc A t I a dt 0 = Δc A t I a dt 0 (12); c A = A λ ε A λ where: c is the concentration change in A-form (E-isomer of azo A-form), I a is A-form absorbed photon flux at the irradiation wavelength using a monochromatic light source, A is the absorbance change at irradiation wavelength using a monochromatic light source, Z is A-form molar extinction coefficient at irradiation wavelength using a monochromatic light source and t is irradiation time. Because the amount of transformed Z-isomer to A-form after the strongly basic anion addition is known, the A-form concentration change was determined by Eq. (13) at low A- to B-form conversion (to eliminate the effect of back B-A thermal transformation that is approximately 10-times slower compared to A-B photochemical transformation). The A-form extinction coefficient at 465 nm was calculated as: A465 = A 465 /c A465 ; where: c A = c Z(without F - ) - c, c = A 375 / Z375 and Z375 = A 375 /c Z(without F - ). The A-form absorbed photon flux I a at irradiation wavelength = 465 nm and incident A-form concentration c A0 was calculated by Eq. (14): I a,a 465 = I 0[ 1 10 [ε A 465 (c A0 Δc)] ]. (14) The incident photon flux I 0 at 465 nm was determined by ferrioxalate (FE) actinometry, according to Eq. (15): 64 ( da FE 390 ) 1 I a, FE 465 dt φ FE 465. ε FE 390. l I 0 = = 1 10 A FE A FE 465 (15), where: a, FE465 is ferrioxalate actinometer absorbed photon flux, A FE is ferrioxalate absorbance at corresponding wavelength using a monochromatic light source, FE390 is ferrioxalate molar extinction coefficient at 390 nm, FE465 is quantum yield of ferrioxalate photochemical conversion and l is the path 5

6 length. Ferrioxalate absorbance at 465 nm (A FE was measured by Ocean Optics SD2000 spectrophotometer. 6

7 Photochemical A/B conversion Because the A-form extinction coefficients at 465 nm for both phenylhydrazones 1 and 2 are known, the amount of photochemically transformed azo A-form to form B was calculated by Eq. (16): c A A 465 A 465 = ~ = ε B 465 ε A 465 1/4ε A 465 ε A 465 (16) A 465 1/3ε A 465 ε A 465 = A 46 3/4ε where the molar extinction coefficients of corresponding B-forms ( B465 ) were extrapolated from the A / B ratio of long-wavelength transitions in calculated UV-Vis spectra of A- and B-forms (M062x 6-31+g(dp) level). The long-wavelength transitions relates to a charge-transfer transition in A-form and n-π* transition in B-form, respectively. Initial concentrations of A-form in solution (c A ) were calculated according to the following equation: c A = c Z (without F ) c, (17) where Δc = ΔA 375 / Z375 and Z375 = A 375 /c - Z(without F ). The photoisomerization extent therefore increases from 20-30% conversion to 84% and 77% after F - anion addition to Z1 and Z2 solution, respectively. If ε B 465 = 1/5ε A 465 is assumed, then photoisomerization extents are 79% and 71%. 7

8 SUPPORTING SCHEMES AND FIGURES Fig. S1. 1 H NMR spectrum of Z2 in DMSO-d 6 before and after irradiation with light of 405 nm wavelength (T = K). Scheme S1. Assumed structure of Z1 dimer at higher concentrations. 8

9 Fig. S2. Calculated relative Gibbs free energies of E1 and Z1 isomers (keto forms) and their enol E1- enol and Z1-enol conformers at the M062x 6-31+g(dp) level in vacuum (T = K; TS transition state). 9

10 E1 Z1 Scheme S2. Calculated geometries of E1 and Z1 isomer keto-forms at the M062x 6-31+g(dp) level in vacuum (T = K). Quantum-chemical calculations failed to detect direct TS from E1 E-isomer. 10

11 E1-enol Z1-enol E1-enolZ1-enolTS Scheme S3. Calculated geometries of E1 and Z1 isomer enol-forms (E1-enol and Z1-enol) and corresponding transition state (TS) for their mutual E-Z (Z-E) thermal isomerization in vacuum at the at the M062x 6-31+g(dp) level (T = K). 11

12 Fig. S3. The time-dependent absorbance changes of isatin phenylhydrazone Z1 at 450nm and 400 nm ( M) after addition of M TBA + F - in DMF (c Z1 = M; c F - = M; T = K; t 1/2 is the reaction half-life calculated from mono-exponential fit of absorbance change at 450 nm). Fig. S4. The Z1-anion interaction pseudo first-oder rate constant (k) dependence on the F - anion concentration (c Z1 = M; T = K). 12

13 Fig. S5. Time-dependet UV-Vis spectrum changes of isatin phenylhydrazone Z1 solution after the TBA + OH - addition in DMF (c Z1 = M; c OH - = M; T = K). Fig. S6. Time-dependet UV-Vis spectrum changes of isatin phenylhydrazone Z1 solution after the TBA + CH 3 COO - addition in DMF (c Z1 = M; c CH3COO - = M; T = K). 13

14 Fig. S7. The time-dependent absorbance changes of isatin phenylhydrazone Z1 at 450nm and 405 nm ( M) after addition of M TBA + CH 3 COO - in DMF (c Z1 = M; c CH3COO - = M; T = K). Fig. S8. The time-dependent absorbance changes of isatin phenylhydrazone Z1 at 450nm and 405 nm ( M) after addition of M TBA + CH 3 COO - in DMF (c Z1 = M; c CH3COO - = M; T = K). 14

15 Fig. S9. 1 H NMR spectrum of Z2 in DMSO-d 6 before and after TBA + F - addition (T = K). Fig. S10. Absorbance change of Z1 + TBA + F - solution at 400nm ( -----) and 450 nm ( -----) in DMF due to 390 s photochemical initialization ( ) and 400 s back thermal relaxation ( ) (c Z1 = M; c F - = M; T = K). Half-life of photochemical transformation (t 1/2 = 43 s) increases due to the Z1 concentration increase (t 1/2 was calculated from mono-exponential fit of absorbance change at 450 nm). 15

16 Fig. S11. Reversible cycles of Z2 + TBA + F - solution absorbance at 450 nm in DMF due to photochemical initialization and back thermal relaxation (26 cycles). Fig. S12. Reversible cycles of Z1 + TBA + OH - solution absorbance at 400 and 450 nm in DMF due to photochemical initialization and back thermal relaxation at two different Z1 concentration (Figures A and B). 16

17 Fig. S13. Dependence of the photochemical A to B transformation rate constant k (s -1 ) on the light intensity in DMF (λ irr = 465 nm; c Z1 = M; c F - = M; T = K). Fig. S14. Dependence of the photochemically induced A to B form transformation conversion (absorbance difference at 450 nm in the initial and photostationary state) on the light intensity in DMF (λ irr = 465 nm; c Z1 = M; c F - = M; T = K). 17

18 MeOH addition The addition of MeOH to 1:TBA + F (or 2:TBA + F) solution mixture in DMF results in the A-form destruction (Fig. S15). The absorption band at 450 nm gradually vanishes after MeOH addition and a new hypsochromic band at approximately 385 nm appears. In the next reaction phase, the new band shifts bathochromically to 395 nm (Figs. S15 and S16). Fig. S15. The UV-Vis spectral changes of 1:TBA + F solution mixture after the addition of different MeOH concentration (solvent: DMF; c Z1 = M; c F - = M; T = K). Fig. S16. Time-dependence of the 1:TBA + F solution mixture absorbance at 470 nm at different MeOH concentration (solvent: DMF; c Z1 = M; c F - = M; T = K). 18

19 Based on the observed spectral changes, we assigned the product structure in the initial reaction phase to enol D-form (Scheme S3). Scheme S3. Gradual A-form transformation to initial Z-isomers in the presence of MeOH. Because MeOH is stronger acid compared to A-form, the thermodynamically more stable tetrabutylammonium methanolate (CH 3 O - TBA + ) is formed. The absorption band appearance with A at 385 nm in the initial reaction phase is therefore the result of azo D-form formation (Fig. S15). The D-form formation is relatively fast reaction. In the next reaction phase (at high MeOH concentration over M), the relatively slow D-form transformation back to the initial isatine phenylhydrazones Z1 and Z2 occurs and this results in the A bathochromic shift to 395 nm. The final UV-Vis and 1 H NMR spectra are almost identical with initial UV-Vis and 1 H NMR spectra spectra of 1 and 2 in MeOH (Figs. S15 and S17). The small A shift results from the increase in solution ionic strength due to the TBA + F - presence. 19

20 Fig. S17. 1 H NMR spectrum of Z1 in DMSO-d 6 before and after TBA + F - addition followed by MeOH addition (T = K). 20

21 ADDITIONAL REFERENCES [60] W.H. Press, S. Teukolsky, W. Vetterling, B. Flannery, Numerical Recipes: The Art of Scientific Computing, Cambridge University Press, New York, [61] Wolfram Research, Inc., Mathematica, Version 9.0, Champaign, IL, [62] P. Klán, J. Wirz, Spectrophotometric Determination of the Reaction Progress, in: J. Coxon, P. Bailey, L. Field, J.A. Gladysz, P. Parsons, P. Stang (Eds.), Photochemistry of Organic Compounds: From Concepts To Practice, John Wiley & Sons Ltd, 2009, Chichester, pp [63] E.S. Galbavy, K. Ram, C. Anastasio, 2-Nitrobenzaldehyde as a chemical actinometer for solution and ice photochemistry, J. Photochem. Photobiol. A Chem., 2010, 209, , [64] T. Lehóczki, É. Józsa, K. Ösz, Ferrioxalate actinometry with online spectrophotometric detection, J. Photochem. Photobiol. A Chem., 2013, 251, 63-68, 21