204
To modify the defect, the cyclometalated Ir(III) complexes with
terpyridine derivatives were synthesized, indicating that these
complexes have high molar extinction coefficients in the longer-
wavelength region (around 520 nm, 104 M−1 cm−1) [20,21] and
high power-conversion efficiency. Therefore, because Ir(III) com-
plexes with tridentate ligands are definitely superior to those with
bidentate ligands, the former complexes may be applicable as sen-
sitizers for DSSCs.
In this study, we report here on the synthesis and characteri-
zation of four novel cyclometalated Ir(III) complexes: [Ir(C∧N∧C)
(ptpy-COOH)]+ (C∧N∧C = 2,6-diphenylpyridinato (dpp, 1); 2,4,6-
triphenylpyridinato (tpp, 2), ptpy-COOH = 4ꢀ-(4-carboxyphenyl)-
2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine) and [Ir(C∧N∧C)(tpy-COOH)]+ (C∧N∧C = 2,6-
diphenylpyridinato (dpp, 3); 2,6-ditolylpyridinato (dtp, 4), tpy-
COOH = 4ꢀ-carboxy-2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine). Because the cyclomet-
alating ligands are strong electron-donors, it is interesting to
investigate how these ligands affect the electronic transitions and
redox potentials of complexes 1–4. In addition, we evaluate the
photovoltaic performance of the dye-sensitized photoelectrodes
containing these Ir(III) complexes.
and ethanol. The precipitate was then recrystallized from chloro-
form/ethanol, filtered and washed with ethanol. Upon drying under
vacuum, the desired product was obtained as a white solid. Yield:
19%. 1H NMR (270 MHz, CDCl3, 25 ◦C, TMS): ı (ppm) 8.73, 2H, d
(J = 5.6 Hz); 8.70, 2H, s; 8.63, 2H, d (J = 8.0 Hz); 7.88, 2H, t (J = 8.3 Hz);
7.60, 1H, m; 7.37, 2H, t (J = 6.1 Hz); 7.13, 1H, d (J = 3.4 Hz); 6.57, 1H,
m.
2.2.3. 4ꢀ-Carboxyl-2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine (tpy-COOH)
Potassium permanganate (4.95 g, 31.3 mmol) was added to
a
warm mixture of 4ꢀ-(2-furyl)-2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine (1.06 g,
2.42 mmol), tert-butanol (145 mL), and H2O (30 mL). The mixture
was filtered through Celite after heating at reflux for 24 h, and the
filtrate was reduced to ca. 50 mL. The solution was then adjusted to
pH 6–7 with 2 M HCl; the product precipitated and was collected by
filtration. Tpy-COOH was isolated as a white solid. Yield: 48%. 1H
NMR (270 MHz, DMSO-d6, 25 ◦C, TMS): ı (ppm) 8.86, 2H, s; 8.76,
2H, d (J = 4.1 Hz); 8.66, 2H, d (J = 8.1 Hz); 8.04, 2H, t (J = 7.7 Hz); 7.54,
2H, t (J = 6.1 Hz).
2.2.4. 4ꢀ-(4-Methoxycarboxyl)-2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine
(tpy-COOMe)
2. Experimental
Sulfuric acid (98%, 1 mL) was added to a suspension of tpy-
COOH (0.456 g, 1.65 mmol) in absolute methanol (150 mL). After
24 h of refluxing, the reaction mixture was allowed to cool to room
temperature. The solution was then adjusted to pH 6–7 with sat-
urated aqueous NaHCO3 solution and methanol was removed by
evaporation. The white precipitate was filtered and washed with
H2O. Tpy-COOMe was isolated as a white solid. Yield: 97%. 1H
NMR (270 MHz, CDCl3, 25 ◦C, TMS): ı (ppm) 8.99, 2H, s; 8.75, 2H, d
(J = 3.9 Hz); 8.62, 2H, d (J = 7.8 Hz); 7.88, 2H, t (J = 7.6 Hz); 7.37, 2H, t
(J = 5.8 Hz); 4.02, 3H, s.
2.1. Materials
IrCl3•3H2O, 2,6-diphenylpyridine (dpp), 2,6-ditolylpyridine
(dtp) and ferrocene were obtained from Wako Pure Chem-
ical Industries. Tetra-n-butylammonium perchlorate (TBAP)
and N-methylpyrrolidone were obtained from Tokyo Chemical
Industry, and TBAP was recrystallized from acetonitorile before
use. Poly(vinylidene fluoride), graphite nanopowder and cis-
diisothiocyanatobis(4,4ꢀ-dicarboxy-2,2ꢀ-bipyridine)ruthenium(II)
(N3) were obtained from Aldrich. TiO2 paste (PECC-K01) was
obtained from Peccell Technologies. All other reagents and sol-
vents were of guaranteed grade or better and were used as
received.
2.2.5. 1-(2-Phenyl-2-oxoethyl)pyridinium iodide
Acetophenone (10.0 g, 79.4 mmol) was added to a solution of
I2 (10.1 g, 78.7 mmol) in pyridine (60 mL), and the reaction mixture
was refluxed for 4 h [23]. A precipitate formed upon cooling to room
temperature and was collected by vacuum filtration, washed with
ether to give a light brown solid and dried in air. Yield: 63%. 1H NMR
(270 MHz, CDCl3, 25 ◦C, TMS): ı (ppm) 9.00, 2H, d (J = 6.5 Hz); 8.74,
1H, dt (J = 7.8, 1.2 Hz); 8.28, 2H, t (J = 6.8 Hz); 8.07, 2H, m; 7.80, 1H,
m; 7.66, 2H, m; 6.49, 2H, s.
2.2. Synthesis of compounds
2.2.1. 4ꢀ-(4-Methoxycarboxyphenyl)-2,2ꢀ:6ꢀ,2“-terpyridine
(ptpy-COOMe)
2-Acetylpyridine (2.68 g, 22.1 mmol), 4-formylbenzoic acid
methyl ester (1.78 g, 10.8 mmol), and sodium hydroxide (0.900 g,
22.5 mmol) were mixed in a mortar with a pestle, and the yellow
mixture was ground until it became a brown powder. The pow-
der was transferred to a suspension of ammonium acetate (15.0 g,
excess) in acetic acid (99.7%, 50 mL) and refluxed for 5 h. The crude
product was precipitated from solution via the addition of water,
collected by filtration and washed with water and ethanol. The pre-
cipitate was then recrystallized from CHCl3/ethanol, filtered and
washed with ethanol. Upon drying under vacuum, the desired prod-
uct was obtained as a white solid. Yield: 38%. 1H NMR (270 MHz,
CDCl3, 25 ◦C, TMS): ı (ppm) 8.76, 2H, s; 8.74, 2H, d (J = 4.6 Hz); 8.68,
2H, d (J = 8.1 Hz); 8.18, 2H, d (J = 8.1 Hz); 7.96, 2H, d (J = 10.8 Hz);
7.89, 2H, t (J = 8.7 Hz); 7.37, 2H, t (J = 5.7 Hz); 3.97, 3H, s.
2.2.6. 2,4,6-Triphenylpyridine (tpp)
Ammonium acetate (50.0 g, excess) was added to a stirred
solution of 1-(2-phenyl-2-oxoethyl)pyridinium iodide (16.7 g,
51.4 mmol) and trans-chalcone (12.0 g, 54.1 mmol) in methanol
(70 mL), and the mixture was refluxed for 4 h [23]. The precipitate
that formed upon cooling was collected by vacuum filtration and
washed with methanol to give a white solid, which was dried in air.
Yield: 38%. 1H NMR (400 MHz, CDCl3, 25 ◦C, TMS): ı (ppm) 8.25, 4H,
d (J = 8.5 Hz); 7.29, 2H, s; 7.82, 2H, m; 7.51, 9H, m.
2.2.7. [IrCl3(ptpy-COOMe)]
IrCl3·3H2O (2.16 g, 5.54 mmol) was added to a solution of
ptpy-COOMe (2.21 g, 6.02 mmol) in DMF (30 mL). The dark brown
reaction mixture was heated at 120 ◦C for 6 h, producing a reddish
brown precipitate that was collected by filtration and washed with
CHCl3 (3 mL × 30 mL), leading to a red powder. Yield: 92%. 1H NMR
(270 MHz, DMSO-d6, 25 ◦C, TMS): ı (ppm) 9.21, 2H, d (J = 4.0 Hz);
9.16, 2H, s; 8.92, 2H, d (J = 8.1 Hz); 8.29, 6H, m; 7.98, 2H, t (J = 8.0 Hz);
3.92, 3H, s.
2.2.2. 4ꢀ-(2-Furyl)-2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine
This compound was synthesized according to minor modifi-
cations of previously published methods [22]. 2-Acetylpyridine
(4.84 g, 40.0 mmol), 2-furaldehyde (1.93 g, 20.0 mmol), and sodium
hydroxide (1.60 g, 40 mmol) were mixed in a mortar with a pestle,
and the yellow mixture was ground until it became a brown pow-
der. The powder was transferred to a suspension of ammonium
acetate (15.0 g, excess) in acetic acid (99.7%, 50 mL) and refluxed
for 6 h. The crude product was precipitated from solution via the
addition of water, collected by filtration and washed with water
2.2.8. [IrCl3(tpy-COOMe)]
This complex was prepared by a procedure identical to that used
to produce [IrCl3(ptpy-COOMe)] except that tpy-COOMe was used