New π-Extended Watersoluble Squaraines as Singlet Oxygen ...

crystallization of a golden solid that was filtered and further crystallized from EtOH (0.420 g, 0.65
mmol, 20.0 %). M.p. [EtOH] 121-122 °C. 1 H NMR (DMSO-d 6 ) δ 7.52 (2H, d, J = 4.5 Hz), 7.26
(2H, s), 6.75 (2H, d, J = 4.5 Hz), 4.94 (4H, t, J = 5.0 Hz), 3.67 (4H, t, J = 5.2 Hz), 3.47-3.32 (16H,
m), 3.19 (6H, s), 3.11 (12H, s). 13 C (DMSO-d 6 ) 163.4, 157.9, 146.0, 128.9, 122.2, 120.1, 113.5,
71.1, 70.7, 70.0, 69.7, 69.5, 57.9, 46.1, 42.4. Anal. Calcd for C 32 H 48 N 6 O 8 : C, 59.61; H, 7.50; N,
13.03; Found: C, 59.76; H, 7.59; N, 12.99.
Preparation of squaraine 1d. A suspension of hydrazone 6d (0.500 g, 1.80 mmol) and squaric
acid (0.103 g, 0.90 mmol) in absolute ethanol (80 ml) was refluxed for 3 h. Upon cooling a dark
green precipitate was formed and filtered at reduced pressure. Crystallization form AcOH gave the
pure compound as a green powder (0.306 g, 0.48 mmol, 53.6 %). M.p. > 300 °C (dec.). 1 H NMR
(DMSO-d 6 ) δ 7.93 (2H, s), 7.61 (2H, d, J = 4.6 Hz), 7.44 (4H, d, J = 8.8 Hz), 7.09 (4H, d, J = 8.8
Hz), 7.0 (2H, d, J = 4.6 Hz), 4.30 (6H, s). The 13 C NMR could not be recorded because of
insufficient solubility. Anal. Calcd for C 28 H 22 Br 2 N 6 O 2 : C, 53.02; H, 3.50; N, 13.25; Found: C,
53.54; H, 3.79; N, 13.23.
Preparation of squaraine 2a. A suspension of squaric acid (0.230 g, 2.01 mmol), pyridine (0.320
g, 4.03 mmol) and chromophore 7a (1.400 g, 4.42 mmol) in a 1:1 toluene/BuOH mixture (40 ml)
was refluxed in a Dean-Stark apparatus for 1.5 h. The resulting deep green solution was chilled at
0°C overnight. A golden precipitate was formed and filtered at reduced pressure. Crystallization
from EtOH/H 2 O gave the pure compound as a golden green powder (0.600 mg, 0.84 mmol, 20 %).
M.p. 172-173 °C. 1 H NMR (DMSO-d 6 ) δ 8.72 (4H, d, J = 6.4 Hz), 7.90 (4H, d, J = 6.4 Hz), 7.87
(2H, d, J = 16.1 Hz), 7.74 (2H, d, J = 4.6 Hz), 7.60 (2H, d, J = 16.1 Hz), 7.33 (2H, d, J = 4.7 Hz),
4.60 (4H, t, J = 4.4 Hz), 3.70 (4H, t, J = 4.7 Hz), 3.44 (4H, m), 3.34 (4 H, m), 3.29 (4H, m), 3.23
(4H, m), 3.12 (6 H, s); 13 C (DMSO-d 6 ) 193.2, 170.4, 147.5, 146.7, 146.4, 130.7, 130.6, 123.5,123.4,
122.1, 116.0, 71.0, 70.9, 70.1, 70.0, 69.5, 57.8, 46.3. Anal. Calcd for C 40 H 46 N 4 O 8 : C, 67.59; H,
6.52; N, 7.88; Calcd for C 40 H 46 N 4 O 8 x 2/3 H 2 O: C, 65.11; H, 6.69; N, 7.59; Found: C, 65.26; H,
6.80; N, 8.13.
Preparation of squaraine 2b. A suspension of squaric acid (0.078 g, 0.68 mmol), pyridine (0.108
g, 1.36 mmol) and chromophore 7b (0.500 g, 1.36 mmol) in a 1:1 toluene/BuOH mixture (40 ml)
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