All chemicals, 4-Bromophenyl hydrazine hydrochloride (98%), Phenyl hydrazine (97%), 2-
aminbenzothiol (99%), 4-(Dimethylamino) benzaldehyde (99%), 1, 4-butanesultone (99%), 3-
iodopropanoic acid (95%), Sodium carbonate anhydrous, TiO2 ≤ 20 nm, Triton X-100 ,dimethyl
sulfoxide, chenodeoxycholic acid (CDCA), polyvinylpyrrolidone, H2PtCl6, NaBH4, iodine, lithium
iodide, 1-butyl-3-methylimidazolium iodide and 4-tertbutylpyridine were purchased from Sigma–
Aldrich. N719 as reference dye [24], ITO glass and Scotch tape were purchased from Solaronix, SA,
Switzerland. Isopropyl methyl ketone (98%), Sodium sulphate anhydrous (99%), Ethyl acetate (99%),
Toluene (99%), Ethanol absolute were purchased from Alfa Aesar.
Instrumental analysis
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All HNMR spectra were recorded using DMSO-d6 and CDCl3 on a Bruker 400 MHz and 13C-NMR
(150 MHz) spectrometer. UV-vis spectra were recorded on a MeOH, Perkin Elmer UV-1800
spectrophotometer. In dried ethanol with three electrode systems, the oxidation / reduction properties of
the HC-IND1, HC-ID2 and HC-BT were examined by cyclic voltammetry (CV) on a Metrohm Autolab
PGSTAT 128N composed of a saturated Ag/AgCl reference electrode, an auxiliary platinum wire
electrode, and a Pt-electrode as working electrode. CV measurement was carried out in room
temperature using methanol solution of 0.1 M tetrabutylammonium hexafluorophosphate (TBAPF6) as
supporting electrolyte and 0.001 M of HC-IND1, HC-TH and HC-IND2 sensitizers with
ferrocene/ferrocenium (Fc/Fc+) as internal standard. The optimisation geometries for IND1, HC-ID2
and HC-BT were calculated using the Gaussian 09 software at the theory level of B3LYP/6-31 (d, p).
Synthesis and characterization of HC-TH, HC-IND1 and HC-IND2 dyes
Synthesis of 2-methylbenzo[d]thiazole(1)
At temperature 150 °C a mixture of 2-aminobenzenethiol (7.46 g, 0.05 mmol) in acetic anhydride.
(30 ml) was refluxed for 4h. It was then cooled to rt. The solvent was removed by distillation. Aqueous
NaOH was added until PH was 8.. It was then extracted with ethyl acetate (3×50 ml) to give compound
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(1) as brown oil in 97% yield. HNMR (400MHz-CDCl3) δ 2.74 (s, 3H, CH3), 7.28 (t,1H, J =5.6 Hz,
Ar-H), 7.39(t, 1H, J= 9.2 Hz, Ar-H), 7.72(d, 1H, J=8.04Hz, Ar-H), 7.94(d, 1H, J=8.16Hz, Ar-H). 13C-
NMR (CDCl3) 19.74(CH3), 121.08, 122.04, 124.38, 125.60 (carbon phenyl aromatic), 148.53, 153.00
(C7, C8 respectively), 166.62(C2).
Synthesis of 2, 3, 3-trimethyl-3H-indole (2)
A mixture of phenylhydrazine (2.7 g, 25 mmol) was added dropwise to 3-methyl-2-butanone
(2.16 g, 25 mmol) , the solution was then heated at 85 ° C for 10 h. 30 ml of water was added and
cooled to room temperature and then extracted by diethyl ether (3×40 ml).The product was dried for 30
min over Na2SO4 , filtered and washed by diethyl ether to get a product red liquid in colour of 95 %
yield. 1HNMR(400MHz-CDCl3) δ1.27(s, 6H, 2CH3), 2.26(s, 3H, CH3), 7.16 (t, 1H, J=0.88 Hz, Ar-H),
7.27 (d t, 2H, J=1.24 Hz, Ar-H), 7.54 (d, 1H, J=7.6Hz, Ar-H). 13C NMR (CDCl3) 15.25(CH3), 22.94
(2CH3), 53.45 (C3), 119.70, 121.19, 125, 127.46(carbon phenyl aromatic), 145. 47, 153.41(C7, C8
respectively), 187.95(C2).
Synthesis of 5-bromo-2, 3, 3-trimethyl-3H-indole (3)
A mixture of p-Bromophenyl hydrazine hydrochloride (7.52 g,0.025mmol), 3-Methyl-2-butanone (5.86
g, 0.015 mmol), and acetic anhydride (50 ml) were refluxed for 6 h under N2 atmosphere and stirred at
room temperature for 16 h. The solvent was removed and the product was extracted with Et2O (3×50
ml) and dried over MgSO4 for 30 min, then filtered and washed with Et2O to give compound (3) as
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brownish oil with 94% yield. HNMR(400MHz-DMSO-d6) δ1.21(s, 3H, CH3), 1.9(s, 6H, 2CH3),
7.45(d, 1H, J=8.2Hz, Ar-H), 7.69(d, 1H, J=8.68Hz , Ar-H) , 7.74(s, 1H, Ar-H). 13C-NMR(CDCl3)
21.68, 21.76 (CH3, 2CH3), 54.52(C3), 118.70, 119.43, 125.6, 139.90(carbon phenyl aromatic), 146.17,
153.26(C8, C9 respectively), 178.98(C2).
Synthesis of 4-(2-methylbenzo[d]thiazol-3-ium-3-yl) butane-1-sulfonate (4)
A mixture of 2-methylbenzothiazole (3g, 0.0201mmol), 1, 4-butanesultone (2.74g, 0.0201 mmol) and
1,2-dichlorobenzene (20 ml) were heated at 110°C for 18h. After cooling to rt, the mixture was diluted
with Et2O (350 ml). The substance was collected through vacuum filtration, washed with Et2O (3×100
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ml) and then vacuum-dried to give compound (4) of 74% yield. HNMR (400MHz-DMSO-d6) δ
1.77(pent, 2H, CH2), 2.07 (pent, 2 H, CH2), 3.22(s, 3H, CH3), 3.30(t, 2 H, J=6.12Hz, N-CH2), 4.47(t,
2H, J=5.4Hz, CH2), 7.79 (t, 1 H, J=7.12Hz, Ar-H), 7.88 (t, 1H, J=7.08Hz, Ar-H), 8.42 (overlapping
doublets, 2H, J = 8.36 Hz, Ar-H). 13C-NMR(DMSO-d6) 16.81(CH3), 21.72(2CH3), 29.76-49.16(4CH2),
116.84, 124.60, 128.09, 129.07, 129.35, 140.80, (carbon phenyl aromatic), 177.02(C2).
Synthesis of 5-bromo-1-(2-carboxyethyl)-2, 3, 3-trimethyl-3H-indolium iodide (5)
A mixture of 5-bromo-2,3,3-trimethyl-3H-indole (4g, 0.0042 mmol), 3-iodopropanoic acid (4.23g,
0.0212 mmol) and nitromethane (30 ml) were refluxed at 110°C for 20h. After cooling to rt, the
mixture was diluted with Et2O (70 ml). The substance was collected through vacuum filtration, washed
with Et2O (3×100 ml) and then vacuum-dried to give compound (5) as an orange solid with 98.75%