D-A-D low band gap molecule containing triphenylamine and benzoxadiazole/benzothiadiazole units: Synthesis and photophysical properties

Article abstract of DOI:10.1016/j.dyepig.2012.04.001

Two D-A-D-type low band gap organic dyes based on triphenylamine and benzoxadiazole/benzothiadiazole, 4,7-Bis{5-{4-{2-[4-(N,N-diphenylamino)phenyl]- 1-nitrilethenyl}phenyl}-2-thienyl}-2,1,3-benzoxadiazole (BDNTBX) and 4,7-Bis{5-{4-{2-[4-(N,N-diphenylamino)phenyl]-1-nitrilethenyl}phenyl}-2-thienyl} -2,1,3-benzothiadiazole (BDNTBT) were successfully synthesized. The properties of two compounds were investigated by density functional theory (DFT) calculations, UV-vis absorption spectroscopy, cyclic voltammetry and fluorescence quenching experiment. The calculated ground-state geometries demonstrate intramolecular charge transfer (ICT) occurs in both molecules during the procedure of charge excitation from HOMO to LUMO. From the data in electrochemistry and fluorescence quenching experiments, the molecules reveal lower HOMO energy levels compared with that of P3HT and proper LUMO energy levels to obtain efficient charge separation with PCBM. Two synthesized compounds exhibit broad absorption range covering the whole visible spectral region. These photophysical and electrochemical properties call attention to that our materials are prospective candidates as donor materials for solution-processable organic photovoltaic cells.

Full text of DOI:10.1016/j.dyepig.2012.04.001

Supporting Information
Table of contents
1. Synthesis details for compounds 4-13
2. 1H NMR and 13C NMRspectra
S2-S3
S3-S11
3. Cyclic voltammetry of P3HT
S11
S12
S12
S12
4. Absorption spectra of [C61]-PCBM and C60.
5. Absorption spectra of compound 2,9 and 13.
6. References
S1

1. Synthesis of compound 4-13
Benzofurazan-N-oxide (4)
NaClO solution (100ml, activated chlorine > 10%) was added dropwise to the mixture of 2-nitroaniline (6.9g,
50mmol) and tetrabutyl ammonium bromide (TBAB, 0.2g, 0.6mmol) in ethyl ether (50ml) and NaOH solution (50%,
4ml). After being stirred at room temperature for 6h, the organic layer was separated, the aqueous layer was
extracted with ethyl ether (3×50ml) and the combined organic layers were dried over anhydrous Na2SO4 and
evaporated to dryness to afford compound 4 (6.5g, 95%) as light yellow solid without further purification. mp
68-69℃(lit,1 69-70℃).
2,1,3-Benzoxadiazole (5)
The solution of compound 4 (6.8g, 50mmol), sulfur (1.6g, 50mmol) and morpholine (0.2ml, 2mmol) in ethylene
glycol (30ml) was stirred at 150℃ for 30min. After being cooled to the room temperature, water (300ml) was
poured to the mixture and the desired compound was purified by steam distillation. The yellow solid in stream
distilled mixture was filtered and dried to afford compound 5 (3.3g, 55%). mp 68-69℃ (lit,2 54℃).
1H-NMR(400MHz, CDCl3, ppm): δ 7.85 (dd, Ja =7.2Hz, Jb = 2.8Hz, 2H), 7.43(dd, Ja = 7.2Hz, Jb = 2.8Hz, 2H).
4,7-Dibromo-2,1,3-benzoxadiazole (6)
The mixture of compound 5 (3.30g, 27.5mmol) and iron (0.31g, 5.5mmol) was heat to 90 ℃ and bromine (4.2ml,
13.2g, 82.5mmol) was added dropwise slowly through 2h. The mixture was stirred at 90℃ for additional 2h,
cooled to the room temperature, and poured into 150ml of water. Then resulting solid was filtered, removed to
200ml saturated NaHCO3, and stirred at room temperature for 60min to neutralize the excess bromine. The crude
product was filtered, dried and purified by silica column chromatograghy eluting with petroleum ether/ethyl acetate
(v:v, 10:1) to afford compound 6 (3.82g, 60%). mp 98-100 ℃ (lit,3 99-100℃).; 1H-NMR(400MHz, CDCl3, ppm):
δ 7.52 (s, 2H).
Tributyl(thiophen-2-yl)stannane (7)
n-BuLi (2.5M in hexane, 12ml, 30mmol) was added dropwise to the solution of thiophene (2.1g, 25mmol) in dry
THF (100ml) under nitrogen atmosphere at -78℃ and the mixture was stirred at that temperature for 1h. Then
tributylchlorostannane (9.75g, 30mmol) was added to the solution. After being stirred at room temperature
overnight, the mixture was poured into water (100ml) and the organic layer was separated, the aqueous layer was
extracted with ethyl ether (3×50ml) and the combined organic layers were dried over anhydrous Na2SO4 and
evaporated to dryness to afford compound 7 as light yellow liquid without further purification.
4,7-Bis(thiophen-2-yl)-2,1,3-benzoxadiazole (8)
A solution of compound 6 (3.0g, 10mmol), tributyl(thiophen-2-yl) stannane (newly prepared, 25mmol) and
Pd(PPh3)2Cl2 (140mg, 0.2mmol) in dry THF (60ml) was refluxed at 70℃ under nitrogen atmosphere overnight.
Then the organic solvent was evaporated under reduced pressure and the crude product was purified by silica
column chromatograghy eluting with petroleum ether/dichloromethane (v:v, 10:1). Recrystallization from ethanol
afforded compound 8 (2.11g, 74%) as red solid. mp 161-163℃, (lit,3 158-159℃). 1H-NMR(400MHz, CDCl3, ppm):
δ 8.12 (dd, Ja =3.8Hz, Jb = 1Hz, 2H), 7.62 (s, 2H), 7.45 (dd, Ja = 5Hz, Jb = 1Hz, 2H), 7.21 (dd, Ja = 3.8Hz, Jb = 5Hz,
2H); APCI MS m/z: 285.0 [(M+H)+] (cacld for C14H8N2OS2 : 284.0078)
4,7-Bis(5-bromothiophen-2-yl)-2,1,3-benzoxadiazole (9)
The solution of compound 9 in 1,2-dichlorobenzene (20ml) was heated to 55 ℃ and N-bromosuccinimide (0.890g,
5mmol) was added. After being stirred at 55℃ for additional 4h, the mixture was heated up to 150℃ for 30min to
redissolve all the solid and cooled to the room temperature. Then the red solid was filtered, washed by 150ml of
water and 150ml of ethanol and dried without further purification to afford compound compound 9 (0.491g, 55%).
mp 226-229℃ (lit,3 229-230℃); 1H-NMR(400MHz, CDCl3, ppm): δ 7.86 (d, J = 4Hz, 2H), 7.49 (s, 2H), 7.16 (d, J
= 4Hz, 2H); MALDI-TOF MS: 439.7731 [M+] (calcd for C14H6Br2N2OS2 : 439.8288)
2,1,3-Benzothiadiazole (10)
Thionyl chloride (8.25g, 70mmol) was added dropwise slowly to the solution of 1,2-diaminobenzene (5.0g,
46.3mmol) and triethylamine (18.7g, 185.0mmol) in dichloromethane (200ml) at room temperature and the mixture
was refluxed for 4h. After being cooled to the room temperature, the solvent was evaporated and water (350ml) was
added. Concentrated HCl was added to the mixture till pH=2. The desired compound was purified by steam
distillation following addition of water to the mixture. The steam distilled mixture was extracted with
dichloromethane (3×100ml) and dried over Na2SO4.The solvent was removed to afford pure compound 10 (5.17g,
82%) as pale yellow solid. mp 42-44℃(lit,4 43-44℃); 1H-NMR(400MHz, CDCl3, ppm): δ 8.02 (dd, Ja = 6.8Hz, Jb =
3.2Hz, 2H), 7.60(dd, Ja = 6.8Hz, Jb = 3.2Hz, 2H).
S2

4,7-Dibromo-2,1,3-benzothiadiazole (11)
A solution of bromine (14.0g, 87.8mmol) in hydrogen bromide (40%, 100ml) was added dropwise slowly to the
mixture of compound 10 (4.0g, 29.4mmol) in hydrogen bromide (40%, 100ml) at room temperature and the mixture
was refluxed at 120℃ for 6h. After being cooled to the room temperature, the excess bromine was neutralized
completely by saturated NaHSO3 and then yellow solid was filtered and washed by a great amount of water. The
resulting residue was dried to afford compound 11 (7.36g, 86%). mp 190-191 ℃ (lit,5 187-188℃);
1H-NMR(400MHz, CDCl3, ppm): δ 7.73 (s, 2H).
4,7-Bis(thiophen-2-yl)-2,1,3-benzothiadiazole (12)
Compound 12 was prepared following the procedure used for compound 8 was obtain compound 12 (2.11g, 74%).
mp 125-126℃(lit,5 124-125℃); 1H-NMR(400MHz, CDCl3, ppm): δ 8.11 (d, J = 3.6Hz, 2H), 7.87 (s, 2H), 7.45 (d, J
= 5.2Hz, 2H), 7.21 (dd, Ja = 5.2Hz, Jb = 4.0Hz, 2H); APCI MS m/z: 301.0 [(M+H)+] (cacld for C14H8N2S3 :
299.9850).
4,7-Bis(5-bromothiophen-2-yl)-2,1,3-benzothiadiazole (13)
A solution of N-bromosuccinimide (2.0g, 11.2mmol) in DMF (15ml) was added to the mixture of compound 12
(1.0g, 3.3mmol) in DMF (100ml) at room temperature under nitrogen atmosphere. After being stirred in darkness
for 24h, the mixture was poured into water (200ml) and the red solid was filtered and dried. Recrystallization from
DMF afforded compound 13 as red needle-like solid (1.01g, 66%). mp 247-249 ℃(lit,5 251-252℃);
1H-NMR(400MHz, CDCl3, ppm): δ 7.81 (d, J = 4Hz, 2H), 7.79 (s, 2H), 7.16 (d, J = 4Hz, 2H); MALDI-TOF MS:
455.7490 [M+] (calcd for C14H6Br2N2S3 : 455.8060)
2. 1H‐NMR spectra
N
CHO
7.70
ppm (t1)
7.60
7.50
7.40
7.30
7.20
7.10
7.00
10.0
5.0
0.0
ppm (t1)
Figure S1. 1H‐NMR of 1 in CDCl3.
S3

NC
Br
N
7.80
ppm (t1)
7.70
7.60
7.50
7.40
7.30
7.20
7.10
7.00
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
ppm (t1)
Figure S2. 1H‐NMR of 2 in CDCl3.
NC
O
B
N
O
7.90
7.80
7.70
7.60
7.50
7.40
7.30
7.20
7.10
ppm (t1)
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
ppm (t1)
Figure S3. 1H‐NMR of 3 in CDCl3.
S4

O
N
N
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
ppm (t1)
Figure S4. 1H‐NMR of 5 in CDCl3.
O
N
N
Br
Br
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
ppm (t1)
Figure S5. 1H‐NMR of 6 in CDCl3.
S5

O
N
N
S
S
8.00
7.50
ppm (t1)
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
ppm (t1)
Figure S6. 1H‐NMR of 8 in CDCl3.
O
N
N
Br
Br
S
S
7.90
7.80
7.70
7.60
7.50
7.40
7.30
7.20
ppm (t1)
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
ppm (t1)
Figure S7. 1H‐NMR of 9 in CDCl3.
S6

S
N
N
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
ppm (t1)
Figure S8. 1H‐NMR of 10 in CDCl3.
S
N
N
Br
Br
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
ppm (t1)
Figure S9. 1H‐NMR of 11 in CDCl3.
S7

S
N
N
S
S
8.00
7.50
ppm (t1)
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
ppm (t1)
Figure S10. 1H‐NMR of 12 in CDCl3.
S
N
N
Br
Br
S
S
7.90
7.80
7.70
7.60
7.50
7.40
7.30
7.20
7.10
ppm (t1)
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
ppm (t1)
Figure S11. 1H‐NMR of 13 in CDCl3.
S8

O
N
N
NC
N
S
S
N
CN
8.00
7.50
7.00
ppm (t1)
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
ppm (t1)
Figure S12. 1H‐NMR of BDNPTBX in CDCl3.
S
N
N
NC
N
S
S
N
CN
8.00
7.50
7.00
ppm (t1)
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
ppm (t1)
Figure S13. 1H‐NMR of BDNPTBT in CDCl3.
S9

NC
Br
N
150
140
130
120
110
100
ppm (t1)
Figure S14. 13C‐NMR of 2 in CDCl3
NC
O
O
B
N
150
100
50
0
ppm (t1)
Figure S15. 13C‐NMR of 3 in CDCl3
S10

S
N
N
CN
N
S
S
NC
N
150
140
130
120
110
ppm (t1)
Figure S16. 13C‐NMR of BDNTBT in CDCl3
3. Cyclic voltammetry of P3HT
0.4
0.2
0.0
Onset= 0.19V
HOMO= -4.99 eV
Onset= -2.16V
LUMO= -2.64 eV
-3
-2
-1
0
1
+
Potential (V vs Fc/Fc )
Figure S14 Cyclic voltammetry curves of P3HT film on glass carbon electrode in 0.1M Bu4NBF4/
MeCN solution at scan rate of 50mV/s.
S11

4. Absorption spectra of [C61]-PCBM and C60 in toluene solution.
5. Absorption spectra of compound 2,9 and 13.
1.0
Compound 2
Compound 9
Compound 13
0.8
0.6
0.4
0.2
0.0
300
400
500
600
Wavelength (nm)
6. References
1. L. K. Dyall, Aust. J. Chem., 1984, 37, 2013.
2. I. Z. Kondyukov, Y. V. Karpychev, P. G. Belyaev, G. K. Khisamutdinov, S. I. Valeshnii, S. P.
Smirnov and V. P. Il'in, Russ. J. Org. Chem., 2007, 43, 635.
3. N. Blouin, A. Michaud, D. Gendron, S. Wakim, E. Blair, R. Neagu-Plesu, M. Belletete, G.
Durocher, Y. Tao and M. Leclerc, J. Am. Chem. Soc., 2008, 130, 732.
4. B. Dasilveiraneto, A. Lopes, G. Ebeling, R. Goncalves, V. Costa, F. Quina and J. Dupont,
Tetrahedron, 2005, 61, 10975.
5. H. Suh, J. Kim, S. H. Park, S. Cho, Y. Jin, J. Kim, I. Kim, J. S. Lee, J. H. Kim, H. Y. Woo and K.
Lee, Polymer, 2010, 51, 390.
S12