Supporting Information Excited State Relaxation Dynamics of Model ...
Supporting Information Excited State Relaxation Dynamics of Model GFP Chromophore Analogs: Evidence for cis-trans isomerism Shahnawaz Rafiq,1 Basanta Kumar Rajbongshi,1 Nisanth N. Nair, Pratik Sen,* and Gurunath Ramanathan* Department of Chemistry Indian Institute of Technology Kanpur Kanpur, 208 016, UP, India
1-These authors contributed equally for this work. *- to whom correspondence must be addressed FAX- +91-512-2597436; [email protected]; [email protected];
S1
General Aspects The melting points were determined in a JSGW melting point apparatus and are uncorrected. Column chromatography was performed with silica gel 100-200 mesh particle size. TLC analyses were performed with MERK Kieselgel 60 F254 plates. 1H NMR spectra were recorded in JEOL 400 (400 MHz) and JEOL 500 (500 MHz) NMR spectrometers in solution of CDCl3 with the solvent as the internal standard.
13C
NMR spectra were recorded in JEOL 400
(100 MHz) and JEOL 500 (125 MHz) NMR spectrometers with complete proton decoupling. IR spectra were recorded on a Bruker Vector 22 FT-IR spectrometer. Mass spectral analyses were carried out on a Waters ESI-QTOF instrument. All solvents were purchased from local company - SD Fine Chemicals and were purified by following established procedures.1 Anhydrous zinc chloride and anhydrous sodium acetate were purchased from SD Fine chemicals and were dried under vacuum before use. Triphenylamine (Sigma-
Aldrich) was used as received. It was used in preparation of tripehylamine aldehyde by Vilsmeier-Haack reaction.2 Acetic anhydride and aniline (SD Fine Chemicals) were distilled prior to use. All other chemicals used in synthesis were purchased from SD Fine Chemicals and used without purification. For spectroscopic studies all the solvents were purchased form SigmaAldrich and were used as such.
General procedure for preparation of (4Z)-4-arylmethylene-2-phenyl-5(4H)-oxazolones (IIIa-b, Scheme 1).3,4 A mixture of N-benzoylglycine, I (1.0 g, 5.6 mmol, 1 equiv.), paradisubstituted aromatic aldehyde, IIa-b (5.6 mmol, 1 equiv.), anhydrous sodium acetate (0.46 g, 5.6 mmol, 1 equiv.) and acetic anhydride (2.6 mL, 28.0 mmol, 5 equiv.) was refluxed for 2 h. The reaction mixture was cooled to room temperature and 10 mL ethanol added and kept at 0 °C for 20 minutes. The deposited solid was filtered under suction and washed with ice-cold ethanol (10 mL ×2) and warm water (50 mL). The crude product obtained was dried in vacuum desiccator. The crude product was purified by a short pad silica gel chromatography (60-120 mesh).
S2
Scheme 1. Synthesis of the GFP chromophore analogs
Results:
(4Z)-4-(4-N,N-Dimethylaminobenzylidene)-2-phenyl-5(4H)-oxazolone (IIIa). Orange powder; Yield 54%; m.p. 182-183 °C; IR (KBr) νmax/cm-1: 1764, 1645, 1606, 1530, 1447, 1374, 1323, 1163, 814; 1H NMR (CDCl3, 400 MHz): δ3.12 (s, 6H, NMe2), 6.75 (d, J = 8.7 Hz, 2H, ArH), 7.21 (s, 1H, =CHAr), 7.48-7.57 (m, 3H, ArH), 8.13-8.16 (m, 4H, ArH);
13
C NMR (CDCl3, 100
MHz): δ40.1, 111.9, 121.9, 126.5, 127.9, 128.5, 128.9, 132.4, 133.5, 135.0, 152.4, 160.7, 168.6; ESI-MS+ m/z Calcd. for C18H17N2O2 293.1290 [M+H], found 293.0999.
S3
(4Z)-4-(4-N,N-Diphenylaminobenzylidene)-2-phenyl-5(4H)-oxazolone (IIIb). Red powder; Yield 69%; m.p. 168-170 °C; IR (KBr) νmax/cm-1: 1706, 1635, 1584, 1491, 1426, 1285, 1152. 1H NMR (CDCl3, 400 MHz): δ7.05 (d, J = 9.7 Hz, 2H, ArH), 7.13-7.20 (m, 7H, =CHAr+ArH), 7.32 -7.35 (m, 4H, ArH), 7.47-7.51 (m, 2H, ArH), 7.54-7.58 (m, 1H, ArH), 8.07 (d, 2H, J = 8.7 Hz, ArH), 8.13 (d, 2H, J = 8.8 Hz, ArH); 13C NMR (CDCl3, 100 MHz): δ120.5, 124.9, 126.1, 126.2, 126.4, 128.2, 128.9, 129.7, 130.6, 132.0, 132.9, 134.1, 146.5, 150.8, 162.0, 168.2; ESI-MS+ m/z Calcd. for C28H21N2O2 417.1603 [M+H], found 417.1607
General procedure for preparation of (4Z)-4-arylmethylene-1-methyl-2-phenyl-1,4dihydro-5H-imidazolin-5-one (1-2, Scheme 1).3,5-7 A mixture of oxazolone (0.34 mmol), methylamine in 40% aqueous solution (0.04 mL, 1.16 mmol) and anhydrous zinc chloride (0.018 g, 0.14 mmol, 40 mol%) was heated at 170 °C for 2h. The reaction mixture was cooled to room temperature and quenched with water. The organic matter was extracted with ethyl acetate (20 mL×3) and washed with saturated sodium bicarbonate solution. The extract was dried over anhydrous sodium sulphate and concentrated to get brown colored crude product. It was further purified by silica gel (100-200 mesh) column chromatography.
S4
Results:
(4Z)-4-(4-N,N-Dimethylaminobenzylidene)-1-methyl-2-phenyl-1,4-dihydro-5H-imidazolin-5one (DMPI). Orange product. Yield 69%; m.p. 162-163 °C; IR (KBr) νmax/cm-1: 1695, 1634, 1587, 1523, 1433, 1367, 1197; 1H NMR (CDCl3, 400 MHz): δ3.06 (s, 6H, NMe2), 3.36 (s, 3H, Me), 6.71 (d, J = 9.2 Hz, 2H, ArH), 7.23-7.26 (m, =CHAr+CHCl3), 7.53 (m, 3H, ArH), 7.84 (m, 2H, ArH), 8.17 (d, J = 8.8 Hz, 2H, ArH); 13C NMR (CDCl3, 125 MHz) δ29.1, 40.3, 112.0, 128.7, 128.8, 129.5, 129.8, 129.9, 130.6, 131.0, 134.8, 151.6, 159.2, 171.6; ESI-MS+ m/z Calcd. for C19H20N3O 306.1606 [M+H], found 306.1609.
(4Z)-4-(4-N,N-Diphenylaminobenzylidene)-1-methyl-2-phenyl-1,4-dihydro-5H-imidazolin-5one (DPMPI). Red product. Yield 60%; m.p. 187-189 °C; IR (KBr) νmaz/cm-1: 1708, 1634, 1584, 1491, 1447, 1382, 1286; 1H NMR (CDCl3, 400 MHz): δ 3.35 (s, 3H, Me), 7.00 (d, J = 8.8 Hz, 2H, ArH), 7.06-7.16 (m, 6H, ArH), 7.19 (s, 1H, =CHAr), 7.26 -7.29 (m, 4H, ArH), 7.47 -7.52 (m, 3H), 7.80 -7.82 (m, 2H, ArH), 8.08 (d, J = 8.5 Hz, 2H, ArH); 13C(CDCl3, 125 MHz): δ29.2, 121.1, 124.4, 125.8, 127.5, 128.7, 128.9, 129.1, 129.6, 129.7, 131.3, 134.0, 137.1, 146.8, 150.0, 160.7, 171.8. ESI-MS+ m/z Calcd for C29H24N3O: 430.1919 [M+H], found 430.1919.
S5
References
1. Perrin, D. D.; Armarego, W.L.F. Purification of Laboratory Chemicals, 4th ed.; ButterworthHeinemann, 1997. 2. Lai, G.; Bu, X. R.; Santos, J.; Mintz, E. A. Synlett 1997, 1275. 3. Badr, M. Z.; El-Sherief, H. A. H.; Tadros, M. E. Bull. Chem. Soc. Jpn. 1982, 55, 2267. 4. Hoshina, H.; Tsuru, H.; Kubo, K.; Igarashi, T.; Sakurai, T. Heterocycles 2000, 53, 2261. 5. Rajbongshi, B. K.; Ramanathan, G. J. Chem. Sci. 2009, 121, 973. 6. Bhattacharjya, G.; Agasti, S. S.; Ramanathan, G. ARKIVOC 2006, 10, 152. 7. Mukerjee, A. K.; Kumar, P. Heterocycles 1981, 16, 1995
Spectral reproduction of oxazolones (IIIa-b) and imidazolin-5-ones (1-2) S6
O O Me2 N
N
Figure S1. 1H NMR (400 MHz, CDCl3) and 13C NMR (100 MHz, CDCl3) of oxazolone IIIa S7
O O N
N
O O N
N
Figure S2. 1H NMR (400 MHz, CDCl3) and 13C NMR (100 MHz, CDCl3) of oxazolone, IIIb
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O N Me N Me 2N
NMe2 V
ArH+CHCl3
Me
ArH ArH
O N Me N Me2 N
Figure S3. 1H NMR (CDCl3, 400 MHz) and 13C NMR (CDCl3, 125 MHz) of (4Z)-4-(4N,N-dimethylaminobenzylidene)-1-methyl-2-phenyl-1,4-dihydro-5H-imidazolin-5-one (1, DMPI).
S9
O
CH3
N CH3 N
N
=CHAr X
O N Me N
N
Figure S4. 1H NMR (CDCl3, 400 MHz) and 13C NMR (CDCl3, 125 MHz) of (4Z)-4-(4-N,Ndiphenylaminobenzylidene)-1-methyl-2-phenyl-1,4-dihydro-5H-imidazolin-5-one (DPMPI) S10
Figure S5a: Logarithmic plots of the femtosecond fluorescence transients of DMPI and DPMPI in different glycerol-methanol mixtures.
Figure S5b: Logarithmic plots of the femtosecond fluorescence transients of DMPI and DPMPI in solvents of different polarity, but with almost similar viscosities.
S11
Figure S6. Logrithmic plots of (a) DMPI and (b) DPMPI depicting the variation of two time constants, τ1 and τ2 with the microviscosity of the glycerol-methanol mixtures.
S12
Figure S7. Calculated potential energy surfaces of ground state (S0) and first excited singlet state (S1) of DMPI (a) as a function of dihedral angle γ(C4-C7-C8-C13) or rotation about the single bond (C7-C8), keeping β fixed at 0° and (b) as a function of dihedral angle β(N3-C4-C7-C8) or rotation about the double bond (C4-C7), keeping γ fixed at 98°. While internal conversion (IC) is very difficult in (a) because of large S0-S1 energy gap, IC is difficult in (b) because of high activation barrier of twisting (30 kcal/mol).
S13
Figure S8. Potential energy profiles of the S0 and S1 states as a function of β (rotation about C4C7 double bond), keeping γ fixed at -2°, computed using TDDFT with and without PCM (acetonitrile)
S14
Spectral reproduction before irradiation of DMPI
O Z N Me N Me2 N
Figure S9. 1H NMR (400 MHz, CDCl3) of (4Z)-4-(4-N,N-dimethylaminobenzylidene)-1-methyl-2-phenyl1,4-dihydro-5H-imidazolin-5-one (1, DMPI).
13
C NMR is shown in Figure S3 S15
Spectral reproduction after irradiation of DMPI (1H NMR) NMe 2 O Z N Me Me2 N
N
O + E N
N Me
Figure S10. 1H NMR (400 MHz, CDCl3) of (4Z)-4-(4-N,N-dimethylaminobenzylidene)-1-methyl-2phenyl-1,4-dihydro-5H-imidazolin-5-one (1, DMPI) and (4E)-4-(4-N,Ndimethylaminobenzylidene)-1-methyl-2-phenyl-1,4-dihydro-5H-imidazolin-5-one (E-DMPI) formed after irradiation of Z-DMPI.
S16
Spectral reproduction after irradiation of DMPI (13C NMR)
NMe 2 O Z N Me N Me2N
O + E N
N Me
Figure S11. 13C NMR (125 MHz, CDCl3) of (4Z)-4-(4-N,N-dimethylaminobenzylidene)-1methyl-2-phenyl-1,4-dihydro-5H-imidazolin-5-one (1, DMPI) and (4E)-4-(4-N,Ndimethylaminobenzylidene)-1-methyl-2-phenyl-1,4-dihydro-5H-imidazolin-5-one (E-DMPI) formed after irradiation of Z-DMPI.
S17
1-These authors contributed equally for this work. *- to whom correspondence must be addressed FAX- +91-512-2597436; [email protected]; [email protected];
S1
General Aspects The melting points were determined in a JSGW melting point apparatus and are uncorrected. Column chromatography was performed with silica gel 100-200 mesh particle size. TLC analyses were performed with MERK Kieselgel 60 F254 plates. 1H NMR spectra were recorded in JEOL 400 (400 MHz) and JEOL 500 (500 MHz) NMR spectrometers in solution of CDCl3 with the solvent as the internal standard.
13C
NMR spectra were recorded in JEOL 400
(100 MHz) and JEOL 500 (125 MHz) NMR spectrometers with complete proton decoupling. IR spectra were recorded on a Bruker Vector 22 FT-IR spectrometer. Mass spectral analyses were carried out on a Waters ESI-QTOF instrument. All solvents were purchased from local company - SD Fine Chemicals and were purified by following established procedures.1 Anhydrous zinc chloride and anhydrous sodium acetate were purchased from SD Fine chemicals and were dried under vacuum before use. Triphenylamine (Sigma-
Aldrich) was used as received. It was used in preparation of tripehylamine aldehyde by Vilsmeier-Haack reaction.2 Acetic anhydride and aniline (SD Fine Chemicals) were distilled prior to use. All other chemicals used in synthesis were purchased from SD Fine Chemicals and used without purification. For spectroscopic studies all the solvents were purchased form SigmaAldrich and were used as such.
General procedure for preparation of (4Z)-4-arylmethylene-2-phenyl-5(4H)-oxazolones (IIIa-b, Scheme 1).3,4 A mixture of N-benzoylglycine, I (1.0 g, 5.6 mmol, 1 equiv.), paradisubstituted aromatic aldehyde, IIa-b (5.6 mmol, 1 equiv.), anhydrous sodium acetate (0.46 g, 5.6 mmol, 1 equiv.) and acetic anhydride (2.6 mL, 28.0 mmol, 5 equiv.) was refluxed for 2 h. The reaction mixture was cooled to room temperature and 10 mL ethanol added and kept at 0 °C for 20 minutes. The deposited solid was filtered under suction and washed with ice-cold ethanol (10 mL ×2) and warm water (50 mL). The crude product obtained was dried in vacuum desiccator. The crude product was purified by a short pad silica gel chromatography (60-120 mesh).
S2
Scheme 1. Synthesis of the GFP chromophore analogs
Results:
(4Z)-4-(4-N,N-Dimethylaminobenzylidene)-2-phenyl-5(4H)-oxazolone (IIIa). Orange powder; Yield 54%; m.p. 182-183 °C; IR (KBr) νmax/cm-1: 1764, 1645, 1606, 1530, 1447, 1374, 1323, 1163, 814; 1H NMR (CDCl3, 400 MHz): δ3.12 (s, 6H, NMe2), 6.75 (d, J = 8.7 Hz, 2H, ArH), 7.21 (s, 1H, =CHAr), 7.48-7.57 (m, 3H, ArH), 8.13-8.16 (m, 4H, ArH);
13
C NMR (CDCl3, 100
MHz): δ40.1, 111.9, 121.9, 126.5, 127.9, 128.5, 128.9, 132.4, 133.5, 135.0, 152.4, 160.7, 168.6; ESI-MS+ m/z Calcd. for C18H17N2O2 293.1290 [M+H], found 293.0999.
S3
(4Z)-4-(4-N,N-Diphenylaminobenzylidene)-2-phenyl-5(4H)-oxazolone (IIIb). Red powder; Yield 69%; m.p. 168-170 °C; IR (KBr) νmax/cm-1: 1706, 1635, 1584, 1491, 1426, 1285, 1152. 1H NMR (CDCl3, 400 MHz): δ7.05 (d, J = 9.7 Hz, 2H, ArH), 7.13-7.20 (m, 7H, =CHAr+ArH), 7.32 -7.35 (m, 4H, ArH), 7.47-7.51 (m, 2H, ArH), 7.54-7.58 (m, 1H, ArH), 8.07 (d, 2H, J = 8.7 Hz, ArH), 8.13 (d, 2H, J = 8.8 Hz, ArH); 13C NMR (CDCl3, 100 MHz): δ120.5, 124.9, 126.1, 126.2, 126.4, 128.2, 128.9, 129.7, 130.6, 132.0, 132.9, 134.1, 146.5, 150.8, 162.0, 168.2; ESI-MS+ m/z Calcd. for C28H21N2O2 417.1603 [M+H], found 417.1607
General procedure for preparation of (4Z)-4-arylmethylene-1-methyl-2-phenyl-1,4dihydro-5H-imidazolin-5-one (1-2, Scheme 1).3,5-7 A mixture of oxazolone (0.34 mmol), methylamine in 40% aqueous solution (0.04 mL, 1.16 mmol) and anhydrous zinc chloride (0.018 g, 0.14 mmol, 40 mol%) was heated at 170 °C for 2h. The reaction mixture was cooled to room temperature and quenched with water. The organic matter was extracted with ethyl acetate (20 mL×3) and washed with saturated sodium bicarbonate solution. The extract was dried over anhydrous sodium sulphate and concentrated to get brown colored crude product. It was further purified by silica gel (100-200 mesh) column chromatography.
S4
Results:
(4Z)-4-(4-N,N-Dimethylaminobenzylidene)-1-methyl-2-phenyl-1,4-dihydro-5H-imidazolin-5one (DMPI). Orange product. Yield 69%; m.p. 162-163 °C; IR (KBr) νmax/cm-1: 1695, 1634, 1587, 1523, 1433, 1367, 1197; 1H NMR (CDCl3, 400 MHz): δ3.06 (s, 6H, NMe2), 3.36 (s, 3H, Me), 6.71 (d, J = 9.2 Hz, 2H, ArH), 7.23-7.26 (m, =CHAr+CHCl3), 7.53 (m, 3H, ArH), 7.84 (m, 2H, ArH), 8.17 (d, J = 8.8 Hz, 2H, ArH); 13C NMR (CDCl3, 125 MHz) δ29.1, 40.3, 112.0, 128.7, 128.8, 129.5, 129.8, 129.9, 130.6, 131.0, 134.8, 151.6, 159.2, 171.6; ESI-MS+ m/z Calcd. for C19H20N3O 306.1606 [M+H], found 306.1609.
(4Z)-4-(4-N,N-Diphenylaminobenzylidene)-1-methyl-2-phenyl-1,4-dihydro-5H-imidazolin-5one (DPMPI). Red product. Yield 60%; m.p. 187-189 °C; IR (KBr) νmaz/cm-1: 1708, 1634, 1584, 1491, 1447, 1382, 1286; 1H NMR (CDCl3, 400 MHz): δ 3.35 (s, 3H, Me), 7.00 (d, J = 8.8 Hz, 2H, ArH), 7.06-7.16 (m, 6H, ArH), 7.19 (s, 1H, =CHAr), 7.26 -7.29 (m, 4H, ArH), 7.47 -7.52 (m, 3H), 7.80 -7.82 (m, 2H, ArH), 8.08 (d, J = 8.5 Hz, 2H, ArH); 13C(CDCl3, 125 MHz): δ29.2, 121.1, 124.4, 125.8, 127.5, 128.7, 128.9, 129.1, 129.6, 129.7, 131.3, 134.0, 137.1, 146.8, 150.0, 160.7, 171.8. ESI-MS+ m/z Calcd for C29H24N3O: 430.1919 [M+H], found 430.1919.
S5
References
1. Perrin, D. D.; Armarego, W.L.F. Purification of Laboratory Chemicals, 4th ed.; ButterworthHeinemann, 1997. 2. Lai, G.; Bu, X. R.; Santos, J.; Mintz, E. A. Synlett 1997, 1275. 3. Badr, M. Z.; El-Sherief, H. A. H.; Tadros, M. E. Bull. Chem. Soc. Jpn. 1982, 55, 2267. 4. Hoshina, H.; Tsuru, H.; Kubo, K.; Igarashi, T.; Sakurai, T. Heterocycles 2000, 53, 2261. 5. Rajbongshi, B. K.; Ramanathan, G. J. Chem. Sci. 2009, 121, 973. 6. Bhattacharjya, G.; Agasti, S. S.; Ramanathan, G. ARKIVOC 2006, 10, 152. 7. Mukerjee, A. K.; Kumar, P. Heterocycles 1981, 16, 1995
Spectral reproduction of oxazolones (IIIa-b) and imidazolin-5-ones (1-2) S6
O O Me2 N
N
Figure S1. 1H NMR (400 MHz, CDCl3) and 13C NMR (100 MHz, CDCl3) of oxazolone IIIa S7
O O N
N
O O N
N
Figure S2. 1H NMR (400 MHz, CDCl3) and 13C NMR (100 MHz, CDCl3) of oxazolone, IIIb
S8
O N Me N Me 2N
NMe2 V
ArH+CHCl3
Me
ArH ArH
O N Me N Me2 N
Figure S3. 1H NMR (CDCl3, 400 MHz) and 13C NMR (CDCl3, 125 MHz) of (4Z)-4-(4N,N-dimethylaminobenzylidene)-1-methyl-2-phenyl-1,4-dihydro-5H-imidazolin-5-one (1, DMPI).
S9
O
CH3
N CH3 N
N
=CHAr X
O N Me N
N
Figure S4. 1H NMR (CDCl3, 400 MHz) and 13C NMR (CDCl3, 125 MHz) of (4Z)-4-(4-N,Ndiphenylaminobenzylidene)-1-methyl-2-phenyl-1,4-dihydro-5H-imidazolin-5-one (DPMPI) S10
Figure S5a: Logarithmic plots of the femtosecond fluorescence transients of DMPI and DPMPI in different glycerol-methanol mixtures.
Figure S5b: Logarithmic plots of the femtosecond fluorescence transients of DMPI and DPMPI in solvents of different polarity, but with almost similar viscosities.
S11
Figure S6. Logrithmic plots of (a) DMPI and (b) DPMPI depicting the variation of two time constants, τ1 and τ2 with the microviscosity of the glycerol-methanol mixtures.
S12
Figure S7. Calculated potential energy surfaces of ground state (S0) and first excited singlet state (S1) of DMPI (a) as a function of dihedral angle γ(C4-C7-C8-C13) or rotation about the single bond (C7-C8), keeping β fixed at 0° and (b) as a function of dihedral angle β(N3-C4-C7-C8) or rotation about the double bond (C4-C7), keeping γ fixed at 98°. While internal conversion (IC) is very difficult in (a) because of large S0-S1 energy gap, IC is difficult in (b) because of high activation barrier of twisting (30 kcal/mol).
S13
Figure S8. Potential energy profiles of the S0 and S1 states as a function of β (rotation about C4C7 double bond), keeping γ fixed at -2°, computed using TDDFT with and without PCM (acetonitrile)
S14
Spectral reproduction before irradiation of DMPI
O Z N Me N Me2 N
Figure S9. 1H NMR (400 MHz, CDCl3) of (4Z)-4-(4-N,N-dimethylaminobenzylidene)-1-methyl-2-phenyl1,4-dihydro-5H-imidazolin-5-one (1, DMPI).
13
C NMR is shown in Figure S3 S15
Spectral reproduction after irradiation of DMPI (1H NMR) NMe 2 O Z N Me Me2 N
N
O + E N
N Me
Figure S10. 1H NMR (400 MHz, CDCl3) of (4Z)-4-(4-N,N-dimethylaminobenzylidene)-1-methyl-2phenyl-1,4-dihydro-5H-imidazolin-5-one (1, DMPI) and (4E)-4-(4-N,Ndimethylaminobenzylidene)-1-methyl-2-phenyl-1,4-dihydro-5H-imidazolin-5-one (E-DMPI) formed after irradiation of Z-DMPI.
S16
Spectral reproduction after irradiation of DMPI (13C NMR)
NMe 2 O Z N Me N Me2N
O + E N
N Me
Figure S11. 13C NMR (125 MHz, CDCl3) of (4Z)-4-(4-N,N-dimethylaminobenzylidene)-1methyl-2-phenyl-1,4-dihydro-5H-imidazolin-5-one (1, DMPI) and (4E)-4-(4-N,Ndimethylaminobenzylidene)-1-methyl-2-phenyl-1,4-dihydro-5H-imidazolin-5-one (E-DMPI) formed after irradiation of Z-DMPI.
S17
