4-Hydroxyphthalonitrile, 1-bromohexadecane, 1-bromotetradecane, 1-octanol, 1-methyl-2-pyrrolidinone (NMP), titanium(IV) butoxide [Ti(OBu)4], I2, tetrabutylammonium iodide (TBAI), ethylene carbonate (EC), and propylene carbonate (PC) were purchased from Sigma-Aldrich Co. Urea was purchased from Shinyo Pure Chemicals Co. All reagents were of analytical grade and used as received without further purification. TiO2 paste, viz. Ti-Nanoxide HT/SP (particle size: 9 nm, wt 20 %), cis-bis(isothiocyanato)bis(2,2′-bipyridyl-4,4′-dicarboxylato)-ruthenium(II) dye (N3 dye), F-doped SnO2 glass (FTO glass), Pt paste (Pt catalyst T/SP), and 1-propyl-3-methylimidazolium iodide (PMImI), were purchased from Solaronix CA.
3.3. Synthesis of TiOPc derivatives 3a and 3b
In the first step, alkoxyphthalonitriles were formed from 4-hydroxyphthalonitrile and 1-bromo-hexadecane or 1-bromotetradecane. 4-Hydroxyphthalonitrile (0.72 g, 5 mmol) and dry potassium carbonate (5.52 g, 40 mmol) was stirred for 30 min under N2 gas in NMP, then a solution of 1-bromohexadecane or 1-bromotetradecane (10 mmol) in NMP was added and the mixture was stirred for 12 h at room temperature. The reaction mixture was filtered and purified by chromatography on a silica column with dichloromethane as the eluent. Yield: 92 % (2a) and 79 % (2b).
2a; FT-IR (KBr, cm−1) : 2917, 2852 (C-H str.), 2232 (C≡N), 1601, 1562 (Ar. C=C str.), 1475 (CH2 bend), 1429 (CH3 bend), 1308, 1251 (C-O); 1H-NMR (δ) 7.72, 7.25, 7.20 (Ar. C-H), 4.05 (-O-CH2-), 1.83 (-O-CH2-CH2-), 1.60 (-CH2-CH3), 1.46, 1.27 (-CH2-), 0.89 (-CH3); Anal calc. for C22H32N2O: C 77.60, H 9.47, N 8.23, O 4.70; found : C 76.30, H 12.20, N 8.17; MS: 340; 2b; FT-IR (KBr, cm−1): 2917, 2851 (C-H str.), 2232 (C≡N), 1603, 1562 (Ar. C=C str.), 1475 (CH2 bend), 1431 (CH3 bend), 1308, 1252 (C-O); 1H-NMR (δ) 7.74, 7.29, 7.20 (Ar. C-H), 4.06 (-O-CH2-), 1.86 (-O-CH2-CH2-), 1.60 (-CH2-CH3), 1.46, 1.27 (-CH2-), 0.89 (-CH3); Anal calc. for C24H36N2O: C 78.21, H 9.85, N 7.60, O 4.34; found : C 79.22, H 13.31, N 8.02; MS: 368;
The second step was the base catalyzed cyclotetramerization of the phthalonitriles. A mixture of alkoxyphthalonitrile (4 mmol), Ti(OBu)4 (0.37 g, 1.1 mmol), urea (0.12 g, 2 mmol), and 1-octanol was heated at 150 °C under N2 for 24 h. After the addition of methanol to the reaction mixture followed by refluxing for 30 min, the resulting deep green blue crystals were collected by filtration, washed with methanol, and then dried in a vacuum oven at 100 °C. Yield: 24 % (3a) and 21 % (3b).
3a; FT-IR (KBr, cm−1) : 2920, 2850 (C-H str.), 1607, 1529 (Ar. C=C str.), 1529, 1468 (CH2 bend), 1383, 1344, 1282 (C-N), 1244, 1120 (C-O), 1074, 1016, 965, 749 (Ti-N); MS MALDI-TOF: 1364 (MH+), 3b; FT-IR (KBr, cm−1): 2915, 2854 (C-H str.), 1752, 1607, 1531 (Ar. C=C str.), 1492, 1464 (CH2 bend), 1367, 1343, 1302 (C-N), 1237, 1120 (C-O), 1073, 1016, 964, 750 (Ti-N); MS MALDI-TOF: 1476 (MH+).
3.4. Fabrication of DSSC devices
We prepared DSSC devices using a quasi-solid state electrolyte containing 3a
as an additive sandwiched with TiO2
adsorbed dyes and Pt-coated electrode as the two electrodes. The structure of the DSSC device is shown in Figure 7
. The FTO/TiO2
/Dye/Electrolyte/Pt device was fabricated using the following procedure; a volume of ca. 10 μL/cm2
of the transparent paste (Ti-Nanoxide HT) was spread on FTO glass by the doctor blade method. After heating the FTO glass covered with TiO2
nanoparticles successively at ca. 100 °C and ca. 450 °C for about 30 min each, the sintering process was completed and the TiO2
deposited electrode was cooled down from 100 °C to ca. 60 °C at a controlled cooling rate (5 °C/min) to avoid the cracking of the glass. A Pt counter electrode was fabricated by spreading on FTO glass using the doctor blade method. After heating the FTO glass spread Pt catalyst T/SP at 100 °C for 10 min, it was fired at 400 °C for 30 min. N3 dye was dissolved in absolute ethanol at a concentration of 20 mg per 100 mL of solution. Nanoporous TiO2
film was dipped in this solution at room temperature for 24 hours. Afterwards, the dye-sensitized TiO2
electrode was rinsed with absolute ethanol and dried in air. Without a sealant, the electrolyte solution was cast onto the TiO2
electrode impregnated with N3 dye and then dried at 55 °C for 2 hours. The electrolyte solution was composed of 24 mg of I2
, 72 mg of TBAI, 80 mg of PMImI as an ionic liquid, 0.32 mL of EC/0.08 mL of PC (EC/PC=4/1 as volume ratio) and 3a
in acetonitrile solution.