Photoinduced Phase Transition of Azobenzene-Coupled Benzenetricarboxamide

Experimental

Materials and Instruments. Unless otherwise stated, all commercially available solvents and reagents were used without further purification. Melting points were recorded on Mettler Toledo MP50 apparatus and are uncorrected. IR spectra were recorded on an FT-IR Smiths Identify IR and the values are mentioned in cm−1. The 1H-NMR and 13C-NMR was recorded on Varian and Bruker NMR spectrophotometer, using commercial NMR solvents obtained from Aldrich with TMS as internal standard and chemical shifts are mentioned in δ ppm scale. The Mass spectra were obtained over Varian 1200L quadrupole MS (EI) spectrophotometer.

4-Bromophenylazoaniline (C12H10BrN3). To a dichloromethane solution (50 mL) containing para-bromoaniline (2.50 g, 14.5 mmol) was added oxone (17.86 g, 29.0 mmol) in water (150 mL). The mixture was kept at room temperature for 4 h and then layers were separated. The aqueous layer was extracted with dichloromethane (100 mL × 3). Combined organic layer was washed with dil. HCl (1 N, 100 mL), sat. NaHCO3 (100 mL), water (100 mL) and brine (100 mL). Drying over anhydrous sodium sulfate was followed by concentration to yield the crude nitroso intermediate (quant.). The crude was then dissolved in glacial AcOH (40 mL) immediately and to this solution was added 1,4-phenylenediamine (1.57 g, 14.5 mmol) in dry DMSO (10 mL). The resultant mixture was stirred at room temperature for two days and then concentrated to remove acetic acid. This crude was taken up in brine (500 mL) and extracted with ethyl acetate (150 mL × 5). The combined organic layer was washed with 10％ NaCl solution (100 mL × 2), dried over anhydrous sodium sulfate, and concentrated to give the crude mass which was purified over silica gel column chromatography (20％EA in hexanes) to yield the pure product as brown solid. Yield: 2.40 g (60％); mp 112-115 ℃; 1H-NMR (300 MHz, CDCl3) δ 4.09 (br, 2H, NH2), 6.74 (d, J = 8.7 Hz, 2H, ArH), 7.60 (d, J = 8.7 Hz, 2H, ArH), 7.72 (d, J = 8.7 Hz, 2H, ArH), 7.80 (d, J = 8.7 Hz, 2H, ArH). HRMS (EI): calculated 275.0058, found 275.0049. IR (neat): 3400, 1625, 1594, 1572, 1461, 1302, 1137, 1066, 1002, 826, 737 cm−1.

N1,N3,N5-Tris(4-((E)-(4-bromophenyl)diazenyl)phenyl) benzene-1,3,5-tricarboxamide (C45H30Br3N9O3). To a solution of benzene-1,3,5-tricarbonyl trichloride (1.00 g, 3.8 mmol) in dry THF (40 mL) was added triethylamine (3.15 mL, 22.6 mmol) and 4-bromophenylazoaniline (3.44 g, 12.4 mmol). The resulting mixture was stirred under a reflux condition for 2 days. The precipitates formed were removed and the filtrate was concentrated in vacuo. The residue was re-dissolved in THF and slowly precipitated with large excess of MeOH. The precipitate obtained was filtered off and washed with MeOH (50 mL) and dichloromethane (20 mL) to yield the product as yellow powder. Yield: 3.70 g (95％); mp ＞ 300 ℃. 1H-NMR (300 MHz, DMSO-d6) δ 7.79-7.86 (m, 12H, ArH), 8.00 (d, J = 9.0 Hz, 6H, ArH), 8.12 (d, J = 9.0 Hz, 6H, ArH), 8.18 (s, 3H, ArH), 11.06 (s, 3H, NH); 13C-NMR (temp. 90 ℃, 125 MHz, DMSO-d6) δ 120.4, 123.0, 123.6, 123.7, 129.5, 131.9, 135.0, 141.7, 148.0, 150.9, 164.3. HRMS (ESI): calculated 979.9943 (M − H+), found 979.9895 (M − H+). IR (neat): 3375, 3085, 1671, 1594, 1525, 1500, 1404, 1304, 1247, 1151, 1065, 1005, 837, 727 cm−1.