A simple artificial light-harvesting dyad as a model for excess energy dissipation in oxygenic photosynthesis

Berera et al. 10.1073/pnas.0508530103.

Supporting Information

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Supporting Figure 6
Supporting Figure 7
Supporting Figure 8
Supporting Figure 9
Supporting Text

Fig. 6. EADS that follow from a global analysis of the transient absorption data of dyad 3 in acetone.

Fig. 7. Target analysis with the model depicted in Fig. 4 Upper for dyad 2 (A) and dyad 3 (B) dissolved in acetone. The corresponding fractions and rate constant are reported in Table 1. The SADS corresponding to the long-lived mix of Pc and carotenoid triplet (T) for dyad 2 displays a substantial negative signal below 500 nm, which probably corresponds to a fraction of carotenoid triplets coexisting with Pc triplets on the time scale of the experiment. This causes some carotenoid ground-state bleach below 500 nm.

Supporting Figure 8

Fig. 8. Transient absorption spectra at different time delays in the region 850-980 nm for dyad 3 dissolved in DMSO. The signal is flat and decays uniformly with the lifetime of the Qy state of Pc, indicating that no transient carotenoid radical is formed.

Supporting Figure 9

Fig. 9. EADS of the vibrationally relaxed excited state of model carotenoid 2' in hexane (red line), THF (blue line), and DMSO (green line), after excitation at 475 nm.

Supporting Text

Synthesis of the Compounds

The ¹H-NMR spectra were recorded on Varian spectrometers at 300 or 500 MHz. Unless otherwise specified, samples were dissolved in deuteriochloroform with tetramethylsilane as internal reference. Mass spectra were obtained with a MALDI-TOF spectrometer. All chemicals were purchased from Aldrich, Acros (Geel, Belgium), or Lancaster Synthesis. The ester carotenoids, methyl 8'-apo-b-caroten-8'-oate (9 double bonds), methyl 6'-apo-b-caroten-6'-oate (10 double bonds), and methyl 4'-apo-b-caroten-4'-oate (11 double bonds), were prepared as described (1, 2), and the corresponding acids were obtained by base catalyzed hydrolysis. Solvents were obtained from EM Science. THF was distilled from sodium metal and benzophenone in a nitrogen atmosphere immediately before use. Toluene was distilled from CaH₂, and dichloromethane was distilled from potassium carbonate. All solvents were stored over the appropriate molecular sieves before use. TLC was done with silica gel-coated glass plates from Analtech. Column chromatography was carried out by using EM Science silica gel 60 with 230-400 mesh.

4-Hexanamidophthalonitrile. A solution of 4-nitrophthalonitrile (5.15 g, 29.77 mmol) in methanol (125 ml) was flushed with N₂, and a portion of 10% Pd/C (0.515 g) was added. This mixture was then stirred under H₂ (50 psi) for 1 h. The catalyst was removed by filtration through celite, and the solvent was distilled under vacuum to obtain the desired amine (3.66 g, 86% yield). A portion of the amine obtained (3.60 g, 25.17 mmol) was dissolved in pyridine (90 ml), then hexanoyl chloride (8.6 ml, 61.52 mmol) was added. The mixture was stirred under N₂ for 2 h. The solvent was distilled under vacuum, and the mixture was redissolved in CH₂Cl₂, washed with 0.1 M HCl five times, and washed with 5% NaHCO₃ three times to neutral pH. The solution was dried over MgSO₄ and filtered, and the solvent was distilled under vacuum. The crude product was chromatographed on silica gel (CH₂Cl₂/MeOH 5%) and 4.30 g (71% yield) of the desired nitrile was obtained. ¹H-NMR (300 MHz, CDCl₃) d 0.92 (3H, t, -CO(CH₂)₄CH₃), 1.36 (4H, m, -CO(CH₂)₂CH₂CH₂CH₃), 1.74 (2H, q, -COCH₂CH₂(CH₂)₂CH₃), 2.43 (2H, t, -COCH₂(CH₂)₃CH₃), 7.62 (1H, s, -NHCO-), 7.74 (1H, d, J = 9 Hz, Bz 3-H), 7.87 (1H, dd, J = 9 Hz, 2Hz Bz 5-H), 8.18 (1H, d, J = 2 Hz, Bz 6-H).

1,2-Dibutoxybenzene. Catechol (technical grade) (13.2 g, 120 mmol) was dissolved in 120 ml of DMF. Potassium carbonate (41.4 g, 300 mmol) and n-butylbromide (49.2 g, 360 mmol) were added, and the reaction mixture was stirred at 95°C under N₂ for 24 h. Portions of potassium carbonate (30 g, 217 mmol) and n-butylbromide (30 g, 219 mmol) were added, and the stirring continued for 3 h. Potassium carbonate (30 g, 217 mmol) was added, and the reaction was continued overnight. The mixture was allowed to cool down to room temperature and ether (1 liter) was added. The organic layer was washed with water six times. The organic layer was dried over magnesium sulfate, the solvent was distilled under vacuum, and the liquid obtained was fractionally distilled at reduced pressure collecting the fraction between 69°C and 73°C. This fraction consisted of pure 1,2- dibutoxybenzene (19.05 g, 70.8% yield). ¹H-NMR (300 MHz, CDCl₃) d(6H, t, - OCH₂CH₂CH₂CH₃), 1.52 (4H, s, -OCH₂CH₂CH₂CH₃), 1.81 (4H, q, -OCH₂CH₂CH₂CH₃), 4.01 (4H, t, -O-CH₂CH₂CH₂CH₃), 6.90 (4H, s, Bz 3,4,5,6-H).

1,2-Dibromo-4,5-dibutoxybenzene. A portion of 1,2-dibutoxybenzene (19.0 g, 86 mmol) was dissolved in CH₂Cl₂ (200 ml) and cooled to 0°C under N₂. Bromine (9.6 ml, 187 mmol) was added slowly, half at 0°C and the other half at room temperature. The reaction mixture was stirred for 2 h. The solution was flushed with N₂ and washed with a 10% NaHSO₃ solution and then with 10% NaHCO₃ solution. The organic layer was dried over Na₂SO₄, and the solvent was distilled under vacuum to yield 31.71 g (95.6%) of the desired dibromobenzene. ¹H-NMR (300 MHz, CDCl₃)d (6H, t, -OCH₂CH₂CH₂CH₃), 1.48 (4H, s, -OCH₂CH₂CH₂CH₃), 1.78 (4H, q, -OCH₂CH₂CH₂CH₃), 3.95 (4H, t, -OCH₂CH₂CH₂CH₃), 7.06 (2H, s, Bz 3,6-H).

4,5-Dibutoxyphthalonitrile. A solution of 1,2-dibromo-4,5-dibutoxybenzene (31.7 g, 83.4 mmol) in DMF (400 ml) was stirred and CuCN (22.8 g, 255 mmol) was added. The mixture was heated to reflux under N₂ for 6 h. The mixture was cooled to room temperature and poured into 1.1 liter of concentrated NH₄OH and bubbled with air for 20 h. The mixture was filtered, and the solid obtained was washed with 10% NH₄OH until the filtrate was clear, then with it was washed with water to neutral pH and air-dried. The crude product was extracted with hexanes in a soxhlet for 1 week. The solvent was reduced to 200 ml and filtered. The solid was recrystallized from CH₂Cl₂ and CHCl₃/hexanes and decolorized with activated carbon. The desired dinitrile (10.53 g) was obtained in 46% yield. ¹HNMR (300 MHz, CDCl₃) d1.00 (6H, t, -OCH₂CH₂CH₂CH₃), 1.51 (4H, s, -OCH₂CH₂CH₂CH₃), 1.85 (4H, q, -OCH₂CH₂CH₂CH₃), 4.06 (4H, t, -O-CH₂CH₂CH₂CH₃), 7.12 (2H, s, Bz 3,6-H).

Zinc-9,10,16,17,23,24-Hexabutoxy-2-Hexanamidophthalocyanine. Portions of 4- hexanamidophthalonitrile (1.5 g, 6.1 mmol) and 4,5-dibutoxyphthalonitrile (2.5 g, 9.1 mmol) were dissolved in 80 ml of dimethoxyethane (DME) and stirred under an ammonia flow at 100°C for 2 h. A portion of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU, 1.3 ml) was added, and the stirring was continued for 15 min. Zinc acetate (1.15 g) was added, and the mixture was stirred at 100°C overnight. The green mixture was cooled to room temperature, and 60 ml of a water/methanol mixture (1:1) was added. The precipitate that formed was collected, washed with water, and dried. The product was purified by column chromatography (silica gel, CHCl₃ / MeOH 1%). Zinc- 9,10,16,17,23,24-hexabutoxy-2-hexanamidophthalocyanine was obtained in 18.5% yield (790 mg). ¹H-NMR (500 MHz, DMSO-CDCl₃) d 1.02 (3H, t, -CO(CH₂)₄CH₃), 1.12 - 1.20 (18H, m, -OCH₂CH₂CH₂CH₃), 1.47 - 1.53 (4H, m, -CO(CH₂)₂CH₂CH₂CH₃), 1.70 - 1.80 (12H, m, -OCH₂CH₂CH₂CH₃), 1.87(2H, q, -COCH₂CH₂(CH₂)₂CH₃), 2.00 - 2.10 (12H, m, -OCH₂CH₂CH₂CH₃), 2.63 (2H, t, -COCH₂(CH₂)₃CH₃), 4.47 - 4.55 (12H, m, -OCH₂CH₂CH₂CH₃), 8.40 (1H, d, J = 8 Hz, Pc 3-H), 8.45 - 8.60 (6H, m, Pc 8,11,15,18,22,25-H), 9.10 (1H, d, J = 8 Hz, Pc 4-H), 9.60 (1H, d, Pc 1-H), 10.6 (1H, s, - NHCO-); MS m/z 1122.4 (M + 1)⁺; UV/vis (95% CHCl₃ / 5% MeOH) 355, 612, and 679 nm.

Zinc-2-Amino-9,10,16,17,23,24-Hexabutoxyphthalocyanine. A portion of the hexanamidophthalocyanine obtained in the above reaction (290 mg, 0.258 mmol) was dissolved in 40 ml of THF and 40 ml of a saturated methanolic solution of KOH. The solution was heated to 75°C and stirred overnight under N₂ after the addition of another 10 ml of THF. The reaction mixture was diluted with chloroform and washed with water (three times). The organic layer was dried over Na₂SO₄ and filtered, and the solvent was distilled at reduced pressure. The desired zinc 2-amino-9,10,16,17,23,24- hexabutoxyphthalocyanine (214 mg) was obtained in 81% yield.

Dyad 1. The 8'-apo-b-caroten-8'-oic acid (49 mg, 0.11mmole) was dissolved in 6 ml of toluene and 2 ml of pyridine. One drop of thionyl chloride was added, and the mixture was stirred under N₂ for 15 min. The solvent was distilled under vacuum and the residue kept under vacuum for an extra 15 min. The residue was redissolved in 2.5 ml of pyridine and 6 ml of dry chloroform. The solution of the aminophthalocyanine prepared above (100 mg, 0.1mol) dissolved in 6 ml of chloroform was added to the solution of the acid chloride and the mixture was stirred overnight under N₂. The reaction mixture was diluted with chloroform, washed with water, and dried under vacuum. The product was purified by flash chromatography (silica, chloroform-methanol 0.2%). A second column (silica, CHCl₃) was necessary to obtained 73 mg (52% yield) of pure carotenophthalocyanine 1. 1H-NMR (500 MHz, DMSO/CDCl₃) d1.03 (6H, m, Car 16- CH₃, Car 17-CH₃), 1.16-1.21 (18H, m, -OCH₂CH₂CH₂CH₃), 1.46 (2H, s, Car-2), 1.59 (2H, s, Car-3), 1.71 (3H, s, Car18), 1.75-1.83 (12H, m, -OCH₂CH₂CH₂CH₃), 1.96 (3H, s, Car-19), 2.0 (5H, m, Car- 20, Car-4), 2.08 (15H, m, -OCH₂CH₂CH₂CH₃, Car-20'), 2.32 (3H, s, Car 19'), 4.50-4.57 (12H, m, -OCH₂CH₂CH₂CH₃), 6.16-6.81 (11H, m, Car-7, 8, 10, 11, 12, 14, 15, 11', 12', 14', 15'), 7.44 (1H, s, J = 10, Car-10'), 8.45-8.6 (7H, m, Pc-3, 8, 11, 15, 18, 22, 25), 9.1 (1H, d, Pc-4), 9.63 (1H, s, Pc-1), 10.4 (1H, s, -NH-CO-); MS m/z: 1437.3 (M )⁺; UV/vis (95% CH₂Cl₂ / 5% MeOH) 352, 454, 616, and 683 nm.

Dyad 2 was prepared by the same procedure described for dyad 1. ¹H-NMR (500 MHz, DMSO/CDCl₃) d 1.01 - 1.04 (6H, m, Car 16-CH₃, Car 17-CH₃), 1.16 - 1.21 (18H, m, -OCH₂CH₂CH₂CH₃), 1.46 (2H, m, Car 2-CH₂), 1.59 (2H, m, Car 3-CH₂), 1.71 (3H, s, Car 18-CH₃), 1.75 - 1.83 (12H, m, -OCH₂CH₂CH₂CH₃), 1.96 (3H, s, Car 19-CH₃), 2.00 (5H, m, Car 20-CH₃, Car-4), 2.08 (15H, m, -OCH₂CH₂CH₂CH₃, Car 20'-CH₃), 2.32 (3H, s, Car 19'-CH₃), 4.50 - 4.57 (12H, m, -O-CH₂CH₂CH₂CH₃), 6.16 - 6.81 (13H, m, Car = CH-), 7.44 (1H, d, J = 10 Hz, Car 10'-H), 8.45 - 8.60 (7H, m, Pc 3,8,11,15,18,22,25-H), 9.10 (1H, d, J = 8 Hz, Pc 4-H), 9.63 (1H, s, Pc 1-H), 10.40 (1H, s, -NHCO-); MS m/z 1466.4 (M + 2)⁺; UV/vis (97% CHCl₃ / 3% MeOH) 356, 476, 616, and 684 nm. UV/vis (THF) 354, 468, 612, and 679 nm.

Dyad 3 was prepared by the same procedure described as for dyad 1. ¹H-NMR (500 MHz, DMSO/CDCl₃) d 0.96 - 0.98 (6H, m, Car 16-CH₃, Car 17-CH₃), 1.12 - 1.21 (18H, m, -OCH₂CH₂CH₂CH₃), 1.41 (2H, m, Car 2-CH₂), 1.56 (2H, m, Car 3-CH₂), 1.65 (3H, s, Car 18-CH₃), 1.75 (12H, s, -OCH₂CH₂CH₂CH₃), 1.91 (3H, s, Car 19-CH₃), 1.92 (3H, s, Car 20-CH₃), 1.95 - 2.00 (5H, m, Car-4, Car 20'-CH₃), 2.08 (15H, m, -OCH₂CH₂CH₂CH₃, Car 19'-CH₃), 4.53 - 4.57 (12H, m, -O-CH₂CH₂CH₂CH₃), 6.05 - 7.32 (16H, m, Car = CH-), 8.29 (1H bs Pc 3-H), 8.65 - 8.73 (6H, m, Pc 8,11,15,18,22,25-H), 9.19 (1H, bs, Pc 4-H), 9.75 (1H, s, Pc 1-H), 10.37 (1H, s, -NHCO-); MS m/z 1491.3 (M)⁺; UV/vis (97% CHCl₃ / 3% MeOH) 356, 476, 616, and 684 nm. UV/vis (THF) 354, 468, 612, and 679 nm.

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