3.3.4. Synthesis of Dye **DF90**

*Synthesis of (E)-(1,1 -di-tert-butyl 6-bromo-6 -(5-formylthiophen-2-yl)-3,3 -dioxo-1H,1 H, 3H,3 H- [2,2 -biindolylidene]-1,1 -dicarboxylate)* (**13**). Pd2(dba)3·CHCl3 (86.0 mg, 0.08 mmol, 0.2 eq.) and P(o-Tol)3 (100.0 mg, 0.32 mmol, 0.7 eq.) were dissolved in toluene (150 mL) and the solution was left under stirring for 15 min. t-Boc-protected 6-6 -dibromoindigo (**11**, 1.50 g, 2.4 mmol, 5.0 eq.) was then added and the mixture stirred at room temperature for additional 15min. A solution of 5-(tributylstannyl)thiophene-2-carbaldehyde 12e (190 mg, 0.48 mmol, 1.0 eq.) in toluene (10 mL) was added and the mixture warmed to 50 ◦C overnight. The solvent was then removed by rotatory evaporation and a mixture of EtOAc:hexane = 1:20 (100 mL) was added to the residue. The insoluble fraction was washed several times with the same mixture, allowing to recover starting material **11**. The organic phase, after evaporation, gave a crude solid which was purified by flash chromatography (CH2Cl2 then CH2Cl2:EtOAc 50:1) to afford aldehyde **13** (310 mg, 0.48 mmol) as a red amorphous solid. Yield 79%. 1H-NMR (200 MHz, CDCl3) δH = 9.95 (1H, s), 8.39 (1H, d, J = 1.5 Hz), 8.27 (1H, d, J = 1.5 Hz), 7.79–7.85 (2H, m), 7.57–7.65 (2H, m), 7.54 (1H, dd, J1 = 7.9, J2 = 1.5), 7.38 (1H, dd, J1 = 8.1, J2 = 1.5). 1.72 (9H, s), 1.69 (9H, s). 13C-NMR{1H} (50 MHz, CDCl3) δC = 182.7, 182.4, 182.3, 152.3, 149.6, 149.5, 149.4, 144.0, 140.1, 137.1, 131.0, 127.7, 126.1, 126.0, 125.0, 124.9, 124.8, 123.0, 122.5, 122.4, 121.7, 120.2, 114.4, 85.2, 85.1, 28.1, 28.0; MS (ESI) m/z 673.0 [M + Na]+.

S*ynthesis of di-tert-butyl (E)-6-(4-(bis(4-(hexyloxy)phenyl)amino)phenyl)-6 -(5-formylthiophen-2-yl)-3,3 dioxo-[2,2 -biindolinylidene]-1,1 -dicarboxylate* (**14**). Pd2(dba)3·CHCl3 (6.0 mg, 0.02 mmol, 0.2 eq.) and P(o-Tol)3 (31.0 mg, 0.10 mmol, 0.7 eq.) were dissolved in THF (4 mL) and the solution was left under stirring for 15 min. Bromoaldehyde **13** (100.0 mg, 0.15 mmol, 1.0 eq.) was then added and the mixture stirred at room temperature for an additional 15 min. A solution of stannane **12c** (220.0 mg, 0.30 mmol, 2.0 eq) in THF (1 mL) was added to the mixture and warmed to 55 ◦C. After 7 h the solvent was removed by rotatory evaporation, the crude residue was dissolved with EtOAc (10 mL) and washed with an aqueous saturated KF solution, then with brine. The organic phase was dried, then removed under vacuum to give a crude product which was purified by flash chromatography (CH2Cl2: Petroleum

ether = 1:1 then CH2Cl2: Ethyl acetate 20:1) to obtain **14** (93 mg, 0.15 mmol) as a red amorphous solid. Yield 61%. 1H-NMR (400 MHz, CD2Cl2) δH 9.95 (1H, s), 8.42 (1H, s), 8.24 (1H, s), 7.83–7.74 (m, 3H), 7.63 (1H, d, J = 3.9Hz) 7.58–7.53 (3H, m), 7.53–7.47 (m, 3H), 7.46 (1H, dd, J1 = 7.8Hz, J2 = 1.5Hz m), 7.12 (4H, d, J = 9.0Hz), 6.98 (2H, d, J = 9.0Hz), 6.89 (4H, d, J = 9.0Hz), 3.97 (4H, d, J = 6.4Hz), 1.82–1.75 (4H, m), 1.66 (9H, s), 1.63 (9H, s), 1.55–1.45 (4H, m), 1.40–1.32 (8H, m), 0.92 (6H, t, J = 5.9 Hz); 13C-NMR{1H} (100 MHz, CD2Cl2) δC = 182.8, 182.7, 182.3, 152.1, 149.9, 149.8, 149.7, 149.3, 148.7, 144.0, 139.8, 139.7, 137.2, 130.4, 127.9, 127.3, 126.2, 126.1, 124.7, 124.6, 124.3, 123.2, 122.2, 122.1, 120.8, 119.2, 115.3, 114.1, 113.5, 84.7, 84.4, 68.3, 31.6, 29.3, 27.8, 25.7, 22.6, 13.8; MS (ESI) Found: m/z 1015.25 [M]+.

*Synthesis of (2E,Z)-3-{5-[(E)-6 -(4-{bis[4-(hexyloxy)phenyl]amino}phenyl)-3,3 -dioxo-1H,1 H, 3H,3 H- [2,2 -biindolyliden]-6-yl]thiophen-2-yl}-2-cyanoprop-2-enoic acid* (**DF90**).To a solution of aldehyde **14** (95 mg, 0.093 mmol, 1 eq) in a mixture of acetonitrile/CH2Cl2 (1:1, 4 mL, dried on molecular sieves) were added cyanoacetic acid (10 mg, 0.12 mmol, 1.3 eq) and dry piperidine (84 mg, 0.99 mmol, 8 eq). The mixture was refluxed for 1 h, then it was cooled and the solvent removed under vacuum. The crude was dissolved in CH2Cl2 (10 mL) and washed with NaOH 0.1M and finally with HCl 0.1M. The organic phase was dried on Na2SO4, then the solvent was removed under vacuum. The crude product was recrystallized from CH2Cl2/ethyl acetate (2:1) to obtain **DF90** (45 mg, 0.093 mmol) as a green solid. Yield 55%. 1H-NMR (400 MHz, THF-d8) δH = 9.99 (2H, br s), 8.39 (1H, s), 7.89 (1H, d, J = 3.9 Hz), 7.70–7.62 (4H, m), 7.52 (2H, d, J = 9.0 Hz), 7.42 (1H, s), 7.38 (1H, d, J = 8.2 Hz), 7.20 (1H, d, J = 8.6 Hz), 7.08–7.05 (4H, m), 6.93 (2H, d, J = 9.0 Hz), 6.88-6.85 (4H, m), 3.95, (4H, t, J = 6.4 Hz), 1.81–1.74 (4H, m), 1.53–1.46 (4H, m), 1.39–1.35 (8H, m), 0.93 (6H, t, J = 7.0 Hz); 13C-NMR{1H} (100 MHz, CDCl3) δC= 188.2, 187.6, 163.4, 157.2, 154.5, 153.8, 153.3, 150.6, 149.2, 146.5, 141.2, 139.9, 137.5, 132.2, 128.5, 128.0, 126.8, 125.2, 124.9, 123.3, 122.2, 121.2, 120.4, 119.5, 119.1, 118.6, 116.5, 116.1, 111.5, 111.1, 110.9, 110.4, 68.8, 32.6, 30.4, 26.8, 23.6, 14.4; FT-IR (neat): ν = 2923 (w), 2853 (m), 1704 (m), 1586 (s), 1505 (s), 1445 (s) cm<sup>−</sup>1. HRMS (ESI) m/z calculated for C54H50N4O6S: 882,3451. Found: 882.3435 [M]<sup>+</sup>.
