2.2. Synthesis
The synthesis of W1
A similar method was previously reported26. A mixture of isonicotinic acid (2.46 g, 20 mmol) and SOCl2 (20 mL) was refluxed for 2 hours then excess SOCl2 was removed under vacuum. The residue was dissolved in dry dichloromethane (40 mL). To the solution was added 4-aminobenzoic acid (2.74 g, 20 mmol) and then triethylamine (5.6 mL, 40 mmol). The reaction mixture was stirred overnight at ambient temperature and dichloromethane was removed by rotary evaporation, the solid then dissolved in 5% NaOH followed by slowly acidified with conc. HCl. Precipitate appears and filtered, washed with water and dried to give W1 as a light yellow solid. Yield, 63.2% 1H NMR (CDCl3) δ 10.1 (s 1H), 8.82 (d, 2H), 7.85-8.13 (dd, 6H) HRMS (ESI, m/z): [M + H]+ calcd for C13H10N2O3, 243.0; found 243.23.
The synthesis of W2
A similar method was previously reported24. Yield, 63.2% 1H NMR (CDCl3) δ 8.78-8.80 (d 2H), 8.35 (s, 1H), 7.83-7.85 (dd, 2H) HRMS (ESI, m/z): [M + H]+ calcd for C9H6N2O2, 175.0; found 175.05.
The synthesis of W3
c was synthesized in a similar procedure as A3 except that 4-aminobenzoic acid was replaced by 4-aminophenol (2.18 g, 20 mmol), c in CH3OH (5 mL) then cyanoacetic acid (0.065 mmol, 5.5 g), was dissolved in CH3OH (10 mL) was added under magnetic stirring. The mixture was reacted at ambient temperature for 3 hours. White precipitated generated and was filtered off, washed by CH3OH to give W3 as a white powder in 58.3% yield. 1H NMR (DMSO) δ 10.80 (s 1H), 9.02-9.03 (d, 2H), 8.36-8.38 (d, 2H), 7.57-7.59 (d, 2H), 6.76-6.79 (d, 2H) HRMS (ESI, m/z): [M + H]+ calcd for C16H11N3O3, 294.0; found 294.08.
The synthesis of ZnTPP
A similar method was previously reported. Yield, 27.2% 1H NMR (DMSO) δ 8.75 (s 2H), 8.15-8.17 (m, 2H), 7.78-7.79 (m, 2H), 5.74 (s, 1H), 3.31 (s, 20H), 1.21 (s, 1H) HRMS (ESI, m/z): [M + H]+ calcd for C44H28N4Zn, 677.0; found 677.16.
2.3. Device fabrication
The detailed preparation procedures of TiO2 nanocrystals, pastes for screen-printing, and nanostructured TiO2 film have been reported by Prof. P. Wang27. A cycloidal TiO2 electrode (~0.28 cm2) was stained by immersing it into a solution containing anchoring molecule (2 mM) in DMF overnight, after removal of the unbound molecules (through three ethanol washings), then the electrode was immersed into a dye solution containing ZnTPP (0.2 mM) in CHCl3/ CH3OH for 2 h, then, washed by acetonitrile solution three times and dried by air flow. The sensitized titania electrode was assembled with a thermally platinized FTO electrode. The electrodes were separated by a 35-µm-thick Bynel (DuPont) hot-melt gasket and sealed up by heating. The internal space was filled with a liquid electrolyte using a vacuum backfilling system. The electrolyte-injecting hole on the counter electrode glass substrate, made with a sand-blasting drill, was sealed with a Bynel sheet and a thin glass cover by heating. The electrolyte used contained 50 mM LiI, 30 mM I2 in acetonitrile solvent. After all these procedures, the cells were located in the oven for heating posttreatment at 100℃ for 30 min and cooled to room temperature before photoelectrochemical measurements.