Synthesis, photophysical and electrochemical properties of perylene dyes

Article abstract of DOI:10.1016/j.dyepig.2014.07.019

Perylene dyes comprising: (i) 4-alkoxyphenylamino moiety in the 9-position as a strong donating group, (ii) cyanoacrylic acid as electron acceptor and anchoring group and (iii) a triple bond as short and rigid linker between perylene core and the acceptor group have been successfully synthesized. Their photophysical (i.e. absorption and emission spectra, molar extinction coefficients, fluorescence quantum yields and lifetime measurements) and electrochemical properties were investigated. The dyes display intense absorption in the visible exhibit high molar absorption coefficients making them good light harvesting materials for ss-DSCs.

Full text of DOI:10.1016/j.dyepig.2014.07.019

Dyes and Pigments 112 (2015) 298e304
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Synthesis, photophysical and electrochemical properties of perylene
dyes
Erica Torres , M aꢀ rio Nuno Berberan-Santos , Maria Jo a~ o Brites a
a
,
b
b
, *
ꢀ
a
LNEG, UES Unidade de Energia Solar, Estrada do Paço do Lumiar, 22, 1649-038 Lisboa, Portugal
CQFM-IST, CQFM e Centro de Química-Física Molecular and IN e Institute of Nanoscience and Nanotechnology, Instituto Superior T ꢀe cnico,
b
Universidade de Lisboa, 1049-001 Lisboa, Portugal
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 15 April 2014
Received in revised form
Perylene dyes comprising: (i) 4-alkoxyphenylamino moiety in the 9-position as a strong donating group,
(
ii) cyanoacrylic acid as electron acceptor and anchoring group and (iii) a triple bond as short and rigid
linker between perylene core and the acceptor group have been successfully synthesized. Their photo-
physical (i.e. absorption and emission spectra, molar extinction coefficients, fluorescence quantum yields
and lifetime measurements) and electrochemical properties were investigated. The dyes display intense
absorption in the visible exhibit high molar absorption coefficients making them good light harvesting
materials for ss-DSCs.
1
July 2014
Accepted 18 July 2014
Available online 29 July 2014
Keywords:
©
2014 Elsevier Ltd. All rights reserved.
Perylene dyes
Alkyne bridge
Cyanoacetic group
Solar cells
ss-DSCs
Light harvesting materials
1
. Introduction
DSCs with liquid electrolyte (iodide/tri-iodide redox couple),
delivering an incident monochromatic photo-to-current conver-
sion efficiency of 87% and yielding a power conversion efficiency of
6.8% (6 mm thick mesoporous TiO film) under standard AM 1.5
2
solar conditions [8]. In comparison, the same sensitizer tested in
Perylene derivatives have been widely applied in various optical
devices due to their excellent photophysical properties (e.g. high
absorption coefficient and high fluorescence quantum yield),
charge transfer properties, as well as outstanding chemical, ther-
mal and photochemical stability [1,2].
solid-state DSC (ss-DSC) yield a power conversion efficiency of only
1.8% (1.8 mm thick mesoporous TiO film), showing that sensitizer
2
Perylene monoimides (PMI) or monoanhydrides (PMA) are be-
ing intensively investigated as sensitizers in dye-sensitized solar
cells (DSCs) [3]. Keeping only one acceptor group, i.e. imide or an-
hydride, and introducing a donor group in the 9-position (such as
diarylamine) proved to be important in order to obtain a favorable
orbital partitioning strength and dipole moment of perylene com-
pounds for DSCs. One way to control optical and electrochemical
properties of perylenes dyes is achieved by functionalizing peri and
bay positions of perylene core with different substituents. In a
simplified view, the peri groups coarsely tune the spectroscopic and
electrochemical properties whereas the bay functional groups
provide an additional fine tuning [4e7]. To date, the PMA derivative
with a bis (4-(2,4,4-trimethylamynopentan-2-yl)phenylamino in 9-
position and phenylthio groups in 1 and 6 positions of perylene
core has shown to be the highest efficient perylene sensitizer in
design needs to be adapted according to the cell type.
Based on the aforementioned, the key challenge is to obtain ef-
ficiencies that are comparable to that for the optimized I /I /volatile
solvent cell by using a Hole Transport Material (HTM), which may be
a solid-state material. However, the poor filling of the mesoporous
semiconductor and short diffusion length of charge carriers in HTM
ꢀ
ꢀ
3
have limited the mesoscopic titania layer to a thickness of 2e3 mm.
To increase the amount of light harvesting by ss-DSCs, organic dyes
with high molar extinction coefficients, broad absorption in visible
spectrum and with suitable geometry for control of molecular
orientation and arrangement on the TiO
Here we report the design, synthesis and characterization of
new perylene dyes (Scheme 1) comprising: (1) 4-
2
surface are needed [9,10].
a
alkoxyphenylamino moiety in the 9-position as a strong donating
group, (2) a cyanoacrylic acid as electron acceptor and anchoring
group and (3) a triple bond as short and rigid linker between per-
ylene core and the acceptor group. The photophysical and elec-
trochemical properties of these dyes were investigated, and the
*
Corresponding author. Tel.: þ351 210924600; fax: þ351 217127195.
E-mail address: mjoao.brites@lneg.pt (M.J. Brites).
http://dx.doi.org/10.1016/j.dyepig.2014.07.019
143-7208/© 2014 Elsevier Ltd. All rights reserved.
0

ꢀ
E. Torres et al. / Dyes and Pigments 112 (2015) 298e304
299
R1
R1
(
i)
Br (ii)
(iii)
N
N
Br
1
2
R2
R2
6b : R = OCH , R = OC H
6 13
5
5
a : R =R = OCH
6a : R =R = OCH
1 2 3
1
2
3
b : R = OCH , R = OC H
1
3
2
6
13
1
3
2
(iv)
R1
NH
N
R1
R2
HO
3
4
: R =R = OCH
1 2 3
R2
: R = OCH , R = OC H
1
3
2
6
13
7
7
a : R =R = OCH
1 2 3
b : R = OCH , R = OC H
6 13
1
3
2
(
v)
R1
R1
N
(vi)
O
CN
N
HOOC
R2
R2
PER-EF-1 : R =R = OCH
8a : R =R = OCH
1 2 3
1
2
3
PER-EF-2 : R = OCH , R = OC H
8b : R = OCH , R = OC H
1 3 2 6 13
1
3
2
6
13
ꢁ
Scheme 1. (i) NBS (1.0 equiv), anhydrous THF, 24 h, r.t.; (ii) diarylamine (1.0 equiv), Pd(OAc) (0.020 equiv), P(t-Bu)
2
3
(0.04 equiv), NaOt-Bu (1.5 equiv), anhydrous toluene, 120 C;
ꢁ
(
iii), NBS (1.0 equiv), anhydrous THF, 24 h, r.t.; (iv) Pd(PPh
3
)
4
(0.1 equiv), PPh
3
(0.1 equiv), CuI (0.1 equiv), 2-propyn-1-ol (2.0 equiv), anhydrous THF and diisopropylamine, 90 C; (v)
ꢁ
Dess-Martin, anhydrous CH Cl
2
2
, 24 h; (vi) cyanoacetic acid (1.5 equiv), ammonium acetate (0.4 equiv), glacial acetic acid, 120 C.
results obtained (high molar absorption coefficients and broad
absorption in solar spectrum) make them promising sensitizers for
solar cells applications.
2.2.1. 3-bromoperylene (2)
A solution of N-bromosuccinimide (NBS) (70.5 mg, 1.0 mmol) in
dry THF (5 mL) was added to a solution of compound 1 (100 mg,
1
.0 mmol) in dry THF (5 mL) and stirred at room temperature under
nitrogen atmosphere for 24 h. The mixture was poured into water
30 mL) and extracted with dichloromethane (30 mL). The organic
layer was dried over anhydrous MgSO . After filtration, the solvent
2
. Experimental section
(
4
2
.1. Materials
was removed under reduced pressure to afford compound 2 as a
ꢁ
yellow solid (128 mg, 98%). m.p.: 237e240 C; IR
n
max (KBr): 2921
Chemicals were purchased from commercial sources and
(
CeH alkyl), 1504, 1493 (C]C aromatic ring), 814, 804 (CeH aro-
used without further purification. Solvents were dried and
distilled immediately prior to use by standard procedures [11].
Vacuum filtration purification was performed using silica gel
1
matic ring), 764 (CeBr); H RMN
3
d (400 MHz; CDCl ): 7.48 (2H, t,
J ¼ 8.0 Hz), 7.58 (1H, t, J ¼ 8.0 Hz), 7.70 (2H, d, J ¼ 8.0 Hz), 7.76 (1H, d,
J ¼ 8.4 Hz), 7.99 (1H, d, J ¼ 8.4 Hz), 8.08 (1H, d, J ¼ 8.4 Hz), 8.15 (1H,
(
230e400 mesh) as the stationary phase in a filter funnel with
porous plate. Tetrabutylammonium hexafluorophosphate
TBAPF -98%) used for cyclic voltammetry (CV) was purified by
d, J ¼ 7.6 Hz), 8.20 (1H, d, J ¼ 7.6 Hz), 8.23 (1H, d, J ¼ 7.2 Hz); HRMS
þ
(
ESI): found [MþH] 330.0045; molecular formula C20
H11Br re-
(
6
þ
quires [MþH] 330.0044.
recrystallization from ethanol and dried under vacuum prior to
use. The polymeric films were prepared from cyclic polyolefin
Zeonex 480 R (average Mw z 480,000, pellets) from Zeon
Chemicals L.P.
2
(
.2.2. General procedure for BuchwaldeHartwing cross-coupling
5a-b)
A mixture of 3-bromoperylene 2 (1.0 equiv), diarylamine (1.0
2
.2. Synthesis
equiv), Pd(OAc)
2
(0.02 equiv), P(t-Bu)
3
(0.04 equiv), NaOt-Bu (1.5
ꢁ
equiv) and dry toluene were stirred at 120 C in nitrogen atmo-
sphere for 24 h. After cooling, water was added and the product was
extracted with ethyl acetate (2 ꢂ 30 mL). The organic layer was
The diarylamines bis(4-methoxyphenyl)amine 3 and 4-(hex-
yloxy)-N-(4-methoxyphenyl)aniline
following reported procedures [12].
4
were synthesized by
4
washed with brine solution and dried over anhydrous MgSO . After

ꢀ
300
E. Torres et al. / Dyes and Pigments 112 (2015) 298e304
filtration, the solvent was removed under vacuum and the product
was quickly purified by vacuum filtration over a short pad of silica
brs), 7.48 (1H, t, J ¼ 8.0 Hz), 7.58 (1H, m), 7.68 (1H, d, J ¼ 8.0 Hz), 7.86
(2H, m), 7.94 (1H, d, J ¼ 8.0 Hz) 8.07 (1H, d, J ¼ 8.0 Hz), 8.18 (2H, m);
13
using a mixture of petroleum ether/CH
2
Cl
2
(9:1 to 8:2) as eluent.
3
C NMR d (500 MHz, CDCl ): 132.5, 132.4, 131.6, 130.6, 130.1, 128.3,
127.7, 126.7, 126.2, 125.2, 125.0, 124.8, 121.3, 121.1, 121.0, 115.2, 114.8,
2
.2.2.1. Bis-(4-methoxy-phenyl)-perylen-3-yl-amine (5a). The gen-
71.0, 68.3, 55.5, 31.6, 29.7, 29.4, 25.8, 22.6, 14.1; HRMS (ESI): found
þ
eral method was used with 3-bromoperylene
0
0
2
(100 mg,
[MþH] 627.1761; molecular formula
C
39
H
34BrNO
2
requires
.303 mmol) and bis(4-methoxyphenyl)amine
3 (70 mg,
[MþH]þ 627.1767.
.303 mmol) to afford 5a (116.6 mg, 45%) as an orange solid. m.p:
ꢁ
217e220 C; IR
n
max (KBr): 2924, 2831 (CeH alkyl),1507,1500 (C]C
2.2.4. General procedure for SonogashiraeHagihara cross-coupling
(7a-b)
ꢀ1 1
aromatic ring), 1242 (CeN), 829, 810 (CeH aromatic ring) cm ; H
RMN (400 MHz; CDCl ): 3.77 (6H, s, OCH
), 6.78 (4H, d, J ¼ 8.0 Hz),
.98 (4H, d, J ¼ 8.0 Hz), 7.47 (1H, t, J ¼ 8.0 Hz), 7.46 (1H, t, J ¼ 8.0 Hz),
.67 (2H, m), 7.83 (1H, d, J ¼ 8.0 Hz), 7.34 (1H, t, J ¼ 8.0 Hz), 7.20 (1H,
brs), 7.83 (1H, d, J ¼ 8.0 Hz Hz), 8.13 (2H, d, J ¼ 8.0 Hz), 8.15 (2H, d,
d
3
3
To
a
solution of 6a/6b (1.0 equiv) in anhydrous THF-
(0.1 equiv),
(0.1 equiv) under nitrogen atmosphere,
6
7
diisopropylamine (10-10 mL) were added Pd(PPh )
CuI (0.1 equiv) and PPh
3 4
3
ꢁ
refluxed at 90 C. 2-propyn-1-ol (2.0 equiv) was added after 2 h.
The reaction mixture was stirred for 24 h. After cooling down to
room temperature, the solvents were removed under vacuum to
dryness. The powdery product obtained was purified by vacuum
filtration over short pad of silica using a mixture of hexane/AcOEt
(9:1 to 8:2) as eluent.
13
J ¼ 8.0 Hz); C NMR
3
d (400 MHz, CDCl ): 154.7, 144.4, 142.6, 134.8,
131.7,131.4,131.2,130.4,128.4,127.8,127.3,126.5,126.4,124.5,123.6,
þ
1
20.9, 120.5, 120.2, 119.8, 114.7, 55.8; HRMS (ESI): found [MþH]
479.1872; molecular formula
C
34
H
25NO
2
requires [MþH]þ
479.1879.
2
.2.2.2. (4-hexyloxy-phenyl)-(4-methoxy-phenyl)-perylen-3-yl-
2.2.4.1. 3-{9-[bis-(4-methoxy-phenyl)-amino]-perylen-3-yl}-prop-2-
amine (5b). The general method was used with 3-bromoperylene 2
100 mg, 0.303 mmol) and 4-(hexyloxy)-N-(4-methoxyphenyl)an-
yn-1-ol (7a). The general method was used with 6a (131.0 mg,
(
0.235 mmol) and 2-propyn-1-ol (27.4
(108.9 mg, 87%) as a red solid. m.p.: 170e172 C; IR
m
L, 0.470 mmol) to afford 7a
ꢁ
iline 4 (90.7 mg, 0.303 mmol) to afford 5b (193.4 mg, 60%) as an
n
max (KBr):
ꢁ
orange solid. m.p.: 127e128 C; IR
n
max (KBr): 2956, 2852 (CeH
2928, 2833 (CeH alkyl), 2215 (C^C), 1501 (C]C aromatic ring),
1239 (CeN), 1035 (CeO alcohol), 829, 810 (CeH aromatic ring)
alkyl), 1508 (C]C aromatic ring), 1239 (CeN), 811 (CeH aromatic
ꢀ
1
1
ꢀ1 1
ring) cm ; H RMN
(
d
(400 MHz; CDCl
3
): 0.91 (3H, t, J ¼ 8.0 Hz),1.34
3 3
cm ; H RMN d (400 MHz; CDCl ): 3.77 (6H, s, OCH ), 4.67 (2H, s),
4H, m); 1.44 (2H, m), 1.76 (2H, m), 3.78 (3H, s, OCH
3
), 3.91 (2H, t,
6.78 (4H, d, J ¼ 8.0 Hz), 6.97 (4H, d, J ¼ 8.0 Hz), 7.18 (1H, d,
J ¼ 8.0 Hz), 7.33 (1H, t, J ¼ 8.0 Hz), 7.53 (1H, t, J ¼ 8.0 Hz), 7.62 (1H, d,
J ¼ 8.0 Hz), 7.83 (1H, d, J ¼ 8.0 Hz), 8.00 (1H, d, J ¼ 8.0 Hz), 8.09 (1H,
d, J ¼ 8.0 Hz), 8.15 (1H, d, J ¼ 8.0 Hz), 8.16 (1H, d, J ¼ 8.0 Hz), 8.18 (1H,
J ¼ 8.0 Hz), 6.79 (4H, d, J ¼ 8.0 Hz), 6.98 (4H, d, J ¼ 8.0 Hz), 7.21 (1H,
brs), 7.34 (1H, t, J ¼ 8.0 Hz), 7.49 (2H, m), 7.67 (2H, m), 7.83 (1H, d,
1
3
J ¼ 8.0 Hz), 8.15 (4H, m); C NMR
3
d (500 MHz, CDCl ):154.8, 154.5,
1
3
1
31.6,131.3,131.2,130.4,128.5,127.9,127.5,126.5,126.2,124.5,123.7,
d, J ¼ 8.0 Hz); C NMR
3
d (400 MHz, CDCl ): 154.9, 145.2, 142.3,
1
2
23.6, 121.7, 120.9, 120.5, 120.2, 119.8, 115.2, 114.5, 68.3, 55.5, 31.6,
134.7, 133.9, 132.6, 132.5, 132.1, 132.0, 131.6, 131.4, 131.3, 130.7, 130.1,
128.6, 128.5, 128.1, 127.9, 127.5, 127.3, 127.1, 126.2, 126.0,125.1, 124.8,
þ
9.4, 25.8, 22.6, 14.1; HRMS (ESI): found [MþH] 549.2656; mo-
lecular formula C39
H35NO
2
requires [MþH]þ 549.2662.
123.9, 121.7, 120.9, 120.7, 119.1, 114.6, 93.1, 84.3, 69.7, 60.4, 55.5, 52;
þ
HRMS (ESI): found [MþH]
533.1973; molecular formula
2
.2.3. General procedure for compounds 6a-b
The products 6a and 6b were synthesized according to the
procedure described in the subchapter 2.2.1.
C
37
H
27NO
3
requires [MþH]þ 533.1985.
2.2.4.2. 3-{9-[(4-hexyloxy-phenyl)-(4-methoxy-phenyl)-amino]-per-
ylen-3-yl}-prop-2-yn-1-ol (7b). The general method was used with
2
.2.3.1. (9-bromo-perylen-3-yl)-bis-(4-methoxy-phenyl)-amine (6a).
6b (87.6 mg, 0.140 mmol) and 2-propyn-1-ol (16.3
to afford 7b (67.7 mg, 80%) as a red solid. m.p.: 105e107 C; IR
m
L, 0.279 mmol)
ꢁ
The general method was used with 5a (60.3 mg, 0.126 mmol) and
n
max
NBS (22.4 mg 0.126 mmol) in dry THF (20 mL) to afford 6a
(KBr): 2924, 2853 (CeH alkyl), 2218 (C^C), 1500 (C]C aromatic
ring), 1238 (CeN), 1029 (CeO alcohol), 825, 808 (CeH aromatic
ꢁ
(
131.4 mg, 94%) as a red solid. m.p.: 208e210 C; IR
nmax (KBr):
ꢀ
1 1
2
925, 2832 (CeH alkyl), 1506, 1502 (C]C aromatic ring), 1240
ring) cm ; H RMN
d
(400 MHz; CDCl
3
): 0.90 (3H, t, J ¼ 8.0 Hz),1.34
ꢀ1
1
(
CeN), 828 (CeH aromatic ring), 611 (CeBr) cm
;
H RMN
(4H, m); 1.44 (2H, m), 1.75 (4H, m), 3.77 (3H, s, OCH
3
), 3.90 (2H, t,
d
(400 MHz; DMSO): 3.71 (6H, s, OCH
3
), 6.86 (4H, d, J ¼ 8.0 Hz), 6.90
J ¼ 8.0 Hz), 4.67 (2H, s), 6.77 (4H, d, J ¼ 8.0 Hz), 6.96 (4H, d,
J ¼ 8.0 Hz), 7.19 (1H, d, J ¼ 8.0 Hz), 7.34 (1H, t, J ¼ 8.0 Hz), 7.56 (1H, t,
J ¼ 8.0 Hz), 7.64 (1H, d, J ¼ 8.0 Hz), 7.84 (1H, d, J ¼ 8.0 Hz), 8.03 (1H,
(
(
(
8
4H, d, J ¼ 8.0 Hz), 7.17 (1H, d, J ¼ 8.0 Hz), 7.46 (1H, t, J ¼ 8.0 Hz), 7.72
1H, t, J ¼ 8.0 Hz), 7.80 (1H, d, J ¼ 8.0 Hz), 7.91 (1H, d, J ¼ 8.0 Hz), 8.02
1H, d, J ¼ 8.0 Hz), 8.19 (1H, d, J ¼ 8.0 Hz), 8.39 (1H, d, J ¼ 8.0 Hz),
d, J ¼ 8.0 Hz), 8.11 (1H, d, J ¼ 8.0 Hz), 8.16 (1H, d, J ¼ 8.0 Hz), 8.18 (1H,
13
13
.41 (1H, d, J ¼ 8.0 Hz), 8.48 (1H, d, J ¼ 8.0 Hz); C NMR
d
(500 MHz,
d, J ¼ 8.0 Hz), 8.21 (1H, d, J ¼ 8.0 Hz); C NMR
3
d (400 MHz, CDCl ):
THF): 155.4, 145.4, 142.6, 133.0, 131.9, 131.4, 131.3, 131.1, 130.8, 129.9,
29.5,127.8,127.2,126.4,126.3,125.9,125.0,123.8,121.5,121.2,121.1,
154.9, 154.6, 152.3, 145.3, 142.7, 142.4, 132.1, 131.4, 130.6, 130.0,
128.2, 127.9, 127.5, 127.3, 127.1, 126.6, 126.1, 125.9, 125.1, 124.9, 123.8,
121.7, 121.5, 120.9, 120.7, 119.1, 118.9, 118.8, 115.2, 114.6, 92.9, 84.4,
1
1
þ
20.0, 114.3, 54.6, 29.2; HRMS (ESI): found [MþH] 557.0974; mo-
lecular formula C34
H
24BrNO
2
requires [MþH]þ 557.0985.
68.4, 60.3, 55.5, 52.0, 31.6, 29.4, 25.8, 22.6, 14.0; HRMS (ESI): found
þ
requires [MþH]þ
[
MþH] 603.2762; molecular formula C42
H37NO
3
2
.2.3.2. (9-bromo-perylen-3-yl)-(4-hexyloxy-phenyl)-(4-methoxy-
603.2768.
phenyl)-amine (6b). The general method was used with 5b
(
(
1
105.4 mg, 0.197 mmol) and NBS (35.1 mg, 0.197 mmol)) in dry THF
2.2.5. General procedure for the compounds (8a-b)
To solution of 1,1,1-Tris(acetyloxy)-1,1-dihydro-1,2-
benziodoxol-3-(1H)-one (Dess-Martin periodinane) (1.5 equiv) in
anhydrous CH Cl (10 mL) was added a solution of compounds 7a/
7b in anhydrous CH Cl (10 mL). The mixture was stirred at room
temperature for 24 h. After complete consumption of the starting
material, a saturated NaHCO solution containing 2.5 g of Na
20 mL) to afford 6b (115.1 mg, 93%) as a red solid. m.p.:
a
ꢁ
88e191 C; IR
n
max (KBr): 2925, 2853 (CeH alkyl), 1501, (C]C
aromatic ring), 1239 (CeN), 825, 803 (CeH aromatic ring), 622, 611
2
2
ꢀ
1 1
(
CeBr) cm ; H RMN
.34 (4H, m), 1.45 (3H, m), 1.75 (2H, m), 3.78 (3H, s, OCH
t, J ¼ 8.0 Hz), 6.76 (4H, d, J ¼ 8.0 Hz), 6.78 (4H, d, J ¼ 8.0 Hz), 7.18 (1H,
d
(400 MHz; CDCl
3
): 0.90 (3H, t, J ¼ 8.0 Hz),
2
2
1
3
), 3.92 (2H,
3
2 2 3
S O

ꢀ
E. Torres et al. / Dyes and Pigments 112 (2015) 298e304
301
(
15 mL) and ethyl ether (15 mL) were added and the mixture was
stirred for more 10 min. The product was extracted with ethyl ether
2 ꢂ 30 mL). The organic layer was dried over anhydrous MgSO
and the solvent was evaporated under vacuum.
7.62 (2H, m), 8.15 (1H, d, J ¼ 8.0 Hz), 8.23 (2H, d, J ¼ 8.0 Hz), 8.28
13
(2H, d, J ¼ 8.0 Hz); C NMR
3
d (400 MHz, CDCl ): 176.5, 155.2, 146.6,
(
4
142.5, 141.9, 135.4, 135.3, 134.6, 132.0, 131.8, 131.1, 131.0, 130.0, 128.3,
128.1, 128.0, 126.7, 126.5, 125.8, 125.5, 125.4, 124.5, 124.2, 124.1,
1
23.0, 121.6, 121.0, 119.0, 115.0, 114.7, 94.8, 94.5, 65.8, 55.5, 15.2;
þ
2
.2.5.1. {9-[bis-(4-methoxy-phenyl)-amino]-perylen-3-yl}-propynal
HRMS (ESI): found [MþH]
598.1876; molecular formula
requires [MþH] 598.1887.
þ
(
8a). The general method was used with 7a (108 mg, 0.203 mmol)
C
40
H
26
N
2
O
4
and Dess-Martin reagent (130 mg, 0.305 mmol) to afford 8a
ꢁ
(
2
1
104 mg, 96%) as a dark red solid. m.p.: 162e163 C; IR
n
max (KBr):
2.2.6.2. 2-cyano-5-{9-[(4-hexyloxy-phenyl)-(4-methoxy-phenyl)-
amino]-perylen-3-yl}-pent-2-en-4-ynoic acid (PER-EF-2). The gen-
eral method was used with 8b (40.0 mg, 0.067 mmol) and 2-
921, 2851 (CeH alkyl), 2170 (C^C), 1640 (C]O aldehyde), 1507,
499 (C]C aromatic ring), 1240 (CeN), 851, 807 (CeH aromatic
ꢀ1 1
ring) cm ; H RMN
(
7
7
d
(400 MHz; CDCl
3
): 3.77 (6H, s, OCH
3
), 6.79
cyanoacetic acid (8.5 mg, 0.001 mmol) to afford PER-EF-2
ꢁ
4H, d, J ¼ 8.0 Hz), 6.97 (4H, d, J ¼ 8.0 Hz), 7.19 (1H, d, J ¼ 8.0 Hz),
(25.5 mg, 55%) as a purple solid. m.p.: 215e216 C; IR
nmax (KBr):
.35 (1H, t, J ¼ 8.0 Hz), 7.62 (1H, t, J ¼ 8.0 Hz), 7.82 (1H, d, J ¼ 8.0 Hz),
3448 (COOH), 2923, 2852 (CeH alkyl), 2345 (C^N), 2171 (C^C),
.87 (1H, d, J ¼ 8.0 Hz), 8.05 (1H, d, J ¼ 8.0 Hz), 8.16 (1H, d,
1507, 1499 (C]C aromatic ring), 1239 (CeN), 825, 807 (CeH aro-
-
J ¼ 8.0 Hz), 8.18 (1H, d, J ¼ 8.0 Hz), 8.19 (1H, d, J ¼ 8.0 Hz), 8.23 (1H,
matic ring) cm 1; 1H RMN
d
(400 MHz; CDCl
3
): 0.83 (3H, t,
13
d, J ¼ 8.0 Hz), 9.56 (1H, s, -CHO); C NMR
d
(400 MHz, CDCl
3
): 176.5,
J ¼ 8.0 Hz), 1.26 (4H, m); 1.36 (2H, m), 1.64 (2H, m), 3.67 (3H, s,
1
1
1
1
55.2, 154.4, 146.4, 142.5, 141.8, 135.4, 134.9, 134.3, 131.9, 131.8,
30.9, 130.5, 130.1, 129.4, 128.3, 128.2, 128.0, 126.7, 126.5, 125.8,
25.5, 125.4, 125.0, 124.2124.0, 123.0, 122.5, 121.2, 121.0, 120.1, 118.9,
18.1, 114.9,114.6, 113.4, 94.8, 94.6, 65.8, 59.3, 55.5, 20.4,15.4; HRMS
ESI): found [MþH] 531.1820; molecular formula C37
OCH
3
), 3.82 (2H, t, J ¼ 8.0 Hz), 6.72 (4H, d, J ¼ 8.0 Hz), 6.84 (4H, d,
J ¼ 8.0 Hz), 7.12 (1H, d, J ¼ 8.0 Hz), 7.31 (1H, m), 7.59 (1H, t,
J ¼ 8.0 Hz), 7.71 (1H, d, J ¼ 8.0 Hz), 7.75 (1H, d, J ¼ 8.0 Hz), 8.16 (1H,
13
brs), 8.24 (2H, brs), 8.28 (2H, d, J ¼ 8.0 Hz); C NMR
d (500 MHz,
þ
(
H
25NO
3
re-
CDCl
3
): 154.5, 154.0, 145.3, 141.8, 141.6, 133.8, 132.3, 131.0.130.4,
þ
quires [MþH] 531.1829.
129.2, 128.5, 127.8, 127.3, 126.4, 125.6, 123.6, 122.5, 120.9, 114.9,
1
14.3, 91.9, 67.5, 55.0, 40.0, 39.8, 39.7, 39.5, 39.3, 39.2, 31.0, 25.0,
þ
2
.2.5.2. {9-[(4-hexyloxy-phenyl)-(4-methoxy-phenyl)-amino]-per-
ylen-3-yl}-propynal (8b). The general method was used with 7b
122.0 mg, 0.203 mmol) and Dess-Martin reagent (129.0 mg,
22.0, 14.0; HRMS (ESI): found [MþH] 668.2660; molecular for-
mula C45
H
36
N
2
O
4
requires [MþH]þ 668.2669.
(
0
.304 mmol) to afford 8b (108 mg, 92%) as a dark red solid. m.p.:
2.3. Film sensitization
The TiO films (with average thickness of 1.5 mm) were prepared
ꢁ
117e120 C; IR
nmax (KBr): 2923 (CeH alkyl), 2170 (C^C), 1647 (C]
O aldehyde), 1499 (C]C aromatic ring), 1238 (CeN), 807 (CeH ar-
2
ꢀ1
1
omatic ring) cm
J ¼ 8.0 Hz), 1.34 (4H, m); 1.44 (2H, m), 1.76 (2H, m), 3.78 (3H, s,
OCH
;
H RMN
d
(400 MHz; CDCl
3
): 0.90 (3H, t,
according to previous reported method [13] onto alkali free (AF54)
thin glass substrates (Pr €a zisions &Optik GmbH). These were
ꢀ5
3
), 3.91 (2H, t, J ¼ 8.0 Hz), 6.78 (4H, d, J ¼ 8.0 Hz), 6.96 (4H, d,
immersed into a 2.5 ꢂ 10 M solution of dye in dichloromethane
J ¼ 8.0 Hz), 7.20 (1H, d, J ¼ 8.0 Hz), 7.36 (1H, t, J ¼ 8.0 Hz), 7.65 (1H, t,
J ¼ 8.0 Hz), 7.84 (1H, d, J ¼ 8.0 Hz), 7.90 (1H, d, J ¼ 8.0 Hz), 8.01 (1H,
d, J ¼ 8.0 Hz), 8.17 (1H, d, J ¼ 8.0 Hz), 8.18 (1H, d, J ¼ 8.0 Hz), 8.19 (1H,
and kept for 24 h at room temperature in the dark.
2.4. Instruments and measurements
13
d, J ¼ 8.0 Hz), 8.20 (1H, d, J ¼ 8.0 Hz), 9.56 (1H, s, -CHO); C NMR
d
(500 MHz, CDCl
36.3, 135.2, 131.7, 131.5, 130.0, 129.7, 129.6, 129.0, 128.3, 128.0,
26.7, 125.9, 125.3, 124.1, 124.1, 122.6, 121.5, 121.3, 120.8, 117.1, 117.9,
3
): 175.6, 155.1, 154.8, 146.2, 142.6, 142.3, 140.8,
1H and 13C NMR spectra were recorded on a Bruker Avance III
400 or a Bruker AV 500b spectrometer, operating at 400 and
500 MHz, respectively. Chemical shifts are reported in ppm
downfield from tetramethylsilane, and coupling constants (J) are
reported in Hz. Melting points were measured on a Reichert
Thermovar apparatus fitted with a microscope and are uncorrec-
ted.The absorption spectra were recorded at room temperature in
quartz cuvettes using a Shimadzu UV-3101PC UVeViseNIR spec-
trophotometer and the fluorescence measurements were obtained
using a Horiba Jobin Yvon Fluorolog 3 spectrometer. Fluorescence
quantum yields of dyes PER-EF-1 and PER-EF-2 were determined
by a comparative method at 298 K using rhodamine 101 in ethanol
1
1
115.2, 114.6, 112.9, 68.3, 55.5, 55.4, 31.6, 29.7, 29.4, 25.8, 22.6, 14.0;
þ
HRMS (ESI): found [MþH]
601.2604; molecular formula
þ
C
42
H
35NO
3
requires [MþH] 601.2611.
2
.2.6. General procedure for the compounds (PER-EF-1 and PER-
EF-2)
A mixture of aldehyde 8a/8b (1.0 equiv), 2-cyanoacetic acid (1.5
equiv), ammonium acetate (0.4 equiv) and glacial acetic acid were
refluxed at 120 C for 1 h under nitrogen atmosphere. The reaction
ꢁ
mixture was then cooled to room temperature and taken up in
sodium bicarbonate solution. The organic phase was separated,
washed with water, dried over anhydrous MgSO , filtered and
4
concentrated under reduced pressure. The residue obtained was
purified by silica preparative chromatography using mixtures of
AcOEt/MeOH (9:1) as eluent.
(
f
¼ 0.96) as the fluorescence standard [14]. Fluorescence mea-
surements in Zeonex films were obtained with a Fluorolog F112A
fluorimeter (Spex, www.jobinyvon.com) in right-angle configura-
tion. Emission spectra were corrected for the spectral response of
the optics and photomultiplier. The films were mounted slightly
ꢁ
away from a 45 angle geometry to minimize specular reflection of
the excitation light. All fluorescence decays were measured by
2
.2.6.1. 5-{9-[bis-(4-methoxy-phenyl)-amino]-perylen-3-yl}-2-
single-photon timing. The system is formed by a diode-pumped
cyano-pent-2-en-4-ynoic acid (PER-EF-1). The general method was
used with 8a (43.7 mg, 0.082 mmol) and 2-cyanoacetic acid
4
solid state mode-locked Nd:YVO laser (Vanguard, Spectra Phys-
ics) delivering 2W of 532 nm light at repetition 76 MHz and pulse
duration of ~ 12 ps that synchronously pumped a cavity-dumped
dye laser (701-2, Coherent, delivering 5e6 ps pulses with 40 nJ
(
10.5 mg, 0.123 mmol) to afford PER-EF-1 (16.5 mg, 34%) as a purple
ꢁ
solid. m.p.: 234e235 C; IR
nmax (KBr): 3447 (COOH), 2921, 2851
ꢀ1
(
CeH alkyl), 2345 (C^N), 2172 (C^C), 1507, 1499 (C]C aromatic
pulse at 3.4 MHz) working with rhodamine 6G. Intensity decay
measurements were made by alternating collection of impulse and
decays with the emission polarizer set at the magic angle position.
Impulses were recorded slightly away from the excitation
ꢀ
1
1
ring), 1241 (CeN), 826, 808 (CeH aromatic ring) cm
(400 MHz; DMSO): 3.71 (6H, s, OCH
), 6.74 (4H, d, J ¼ 8.0 Hz), 6.90
4H, d, J ¼ 8.0 Hz), 7.17 (1H, d, J ¼ 8.0 Hz) 7.34 (2H, m), 7.56 (1H, s),
; H RMN
d
3
(

ꢀ
302
E. Torres et al. / Dyes and Pigments 112 (2015) 298e304
1
1
0
0
0
0
0
.2
.0
.8
.6
.4
.2
.0
1.2
5
5
7
7
8
8
a
b
a
b
a
b
5a
5b
7a
7b
8a
8b
(a)
(b)
1.0
0.8
0.6
0.4
0.2
0.0
400
500
600
700
500
600
700
800
900
Wavelength, nm
Wavelength, nm
ꢀ
5
Fig. 1. (a) Normalized absorption spectra of intermediates 5a, 5b, 7a, 7b, 8a and 8b in toluene (2.5 ꢂ 10 M); (b) Normalized emission spectra of intermediates 5a, 5b, 7a, 7b, 8a
and 8b in toluene (2.5 ꢂ 10ꢀ M,
5
l
exc ¼ 450 nm).
wavelength at 562 nm with a scattering suspension, thus defining
the instrument responds function (IRF). For the decays, a cut-off
filter was used to effectively remove excitation light. Emission
light was passed through a depolarizer before reaching the Jobin-
Yvon HR320 monochromator with a grating of 100 lines/mm
which select the fluorescence light from the samples with a
bandwidth of 15e20 nm. The fluorescence was detected by a
Hamamatsu 2809U-01 microchannel plate photomultiplier. No less
than 20,000 counts were accumulated at the maximum channel.
Solutions of the samples were contained in 1 cm path-length quartz
cells at the optical density below 0.1 for fluorescence studies. Cyclic
voltammetry (CV) was carried out at room temperature using a
three electrode cell in potentiostat/galvanostat Gamry Instrument
reference 600. The scan rate was 50 mV/s. A platinum disk, plat-
inum wire and Ag/AgCl (3 M KCl solution) were used as working
compounds 5a, 5b, 7a and 7b were purified by rapid vacuum
filtration through a pad of silica, in lieu of column chromatography,
which is more amenable to scale-up. All the new compounds were
characterized by IR, NMR, and high-resolution mass spectral anal-
ysis. The spectral data were consistent with the proposed struc-
tures. The dyes are reasonable soluble in dichloromethane,
chloroform, tetrahydrofuran, dimethylformamide and toluene.
3.2. Spectroscopic characterization
Fig. 1 shows the absorption (Fig. 1a) and emission (Fig. 1b)
spectra of intermediates 5a, 5b, 7a, 7b, 8a and 8b in toluene and the
results are summarized in Table 1. It is noteworthy that the spectra
of these compounds are almost identical. This implies that the
substituents at the donor group have a small influence on the
(
WE), counter (CE) and reference electrodes, respectively. The
supporting electrolyte was a solution of 0.1 M tetrabutylammonium
hexafluorophosphate (TBAPF in anhydrous N,N-dime-
frontier orbitals of the perylene p-system. The peak position and
the shape are similar for all pairs of intermediates showing that
there is little difference in the electronic structure of the excited
singlet state.
As expected, the introduction of the ethyne-bridge (7a and 7b)
followed by the aldehyde functional group (8a and 8b) led to a red-
shift of the absorption maximum of 21 and 30 nm respectively,
observed for both alkyl substituents (methyl or hexyl).
The normalized emission spectra of all intermediates in toluene
solution present an emission maximum between 630 nm and
6
)
ꢀ
3
thylformaldehyde, with concentration of dyes fixed at 1 ꢂ 10 M .
The potential was calibrated against ferrocene/ferrocenium couple
þ
(
Fc/Fc ). The HOMO energy level was calculated using the following
onset
onset
equation: EHOMO ¼ ꢀ (EOx þ 4.75) eV, where Eox is the onset
þ
oxidation potential versus Ag/Ag [15].
3
. Results and discussion
655 nm, however in the case of 5a, 5b, 7a and 7b, a high energy
shoulder is observed around 530 nm, which could be due to an
excited-state rotamer with weak intramolecular charge-transfer
3.1. Synthesis and characterization
(
ICT). To clarify this situation, drop-cast films of each intermedi-
The synthetic route towards PER-EF-1 and PER-EF-2 is shown
in Scheme 1. The diarylamines bis(4-methoxyphenyl)amine 3 and
-(hexyloxy)-N-(4-methoxyphenyl)aniline 4 were synthesized ac-
ate in zeonex were prepared and the emission spectra recorded. In
4
cording to earlier published procedures [12]. The synthesis com-
mences with the monobromation of 1 with N-bromosuccinimide
Table 1
Optical properties of intermediates 5a, 5b, 7a, 7b, 8a, 8b, perylene molecule and
dyes PER-EF-1 and PER-EF-2 (2.5 ꢂ 10ꢀ M) in toluene at room temperature.
5
(
(
NBS) in dry THF to afford 3-bromoperylene 2 in very high yield
98%) which was used in the next step without further purification.
max (nm) (ε/M cmꢀ1)a
ꢀ1
max (nm)b
l
Stokes shift (Dl/nm)c
Compounds
l
Introduction of donor group in perylene core was carried out by
Buchwald-Hartwing coupling reaction of compound 2 with dia-
rylamine 3 and 4 to afforded 5a and 5b in moderated yields (45%
and 60% respectively). Selective bromination of 5a and 5b with NBS
in THF, followed by Sonogashira-Hagihara cross-coupling reaction
of 6a and 6b with 2-propyl-1-ol afforded 7a and 7b in 87% and 80%
yields respectively. Synthesis of PER-EF-1 and PER-EF-2 was ful-
filled through selective oxidation of allylic alcohols 7a and 7b with
Dess-Martin reagent followed by Knoevenagel reaction of alde-
hydes 8a and 8b with cyanoacetic acid. Compounds 2, 6a, 6b, 8a
and 8b were used in the next step without further purification and
Perylene
440 (34,000)
485 (36,000)
486 (36,400)
506 (37,000)
507 (37,000)
535 (37,600)
536 (39,800)
506 (41,000)
493 (40,000)
444
630
638
644
645
651
655
695
695
4
145
152
138
138
116
119
189
202
5
5
a
b
7a
7
8
8
b
a
b
PER-EF-1
PER-EF-2
a
Maximum of absorption spectra and respective molar absorption coefficient.
Maximum of emission spectra.
Stokes shift.
b
c

ꢀ
E. Torres et al. / Dyes and Pigments 112 (2015) 298e304
303
1
1
0
0
0
0
0
.2
.0
.8
.6
.4
.2
.0
5
5
7
7
a
b
a
b
Fig. 4. (a) Dyes in toluene solution and (b) adsorbed on TiO2 films.
5
00
550
600
650
700
Wavelength, nm
Table 2
Fluorescence quantum yield (
Fig. 2. Normalized emission spectra of intermediates 5a, 5b, 7a and 7b in Zeonex films.
exc ¼ 450 nm).
f
F
), radiative lifetime (
t
/ns), radiative rate constants
ꢀ
1
ꢀ1
(
l
(k
R
/s ) and non-radiative rate constants (kNR/s ) of compounds in toluene.
ꢀ
1
ꢀ1
k
NR (S)
Compounds
f
F
t
(ns)
k
R (S)
8
7
7
8
8
8
8
8
8
7
7
7
6
6
7
7
7
7
Perylene
5a
5b
0.95
0.63
0.66
0.97
0.94
0.66
0.72
0.89
0.88
4.0
7.2
7.2
6.5
7.0
4.4
4.0
5.1
5.1
2.4 ꢂ 10
8.8 ꢂ 10
9.2 ꢂ 10
1.5 ꢂ 10
1.4 ꢂ 10
1.5 ꢂ 10
1.8 ꢂ 10
1.8 ꢂ 10
1.7 ꢂ 10
1.3 ꢂ 10
5.1 ꢂ 10
4.7 ꢂ 10
4.6 ꢂ 10
8.7 ꢂ 10
7.7 ꢂ 10
7.0 ꢂ 10
2.2 ꢂ 10
2.4 ꢂ 10
this rigid medium, excited-state intramolecular rotation of bulky
groups is prevented. As shown in Fig. 2, the aforementioned
shoulder around 530 nm almost disappears for 7a and 7b, but
becomes dominant for 5a and 5b, thus reflecting a different angular
distribution of conformers in the ground state. In the case of 5a and
7
7
8
8
a
b
a
b
5
b, where ICT is weaker, the short wavelength emitting conformer
PER-EF-1
PER-EF-2
dominates, whereas the opposite is observed for 7a and 7b, as
expected.
The absorption spectra recorded for PER-EF-1 and PER-EF-2 in
toluene, at different concentration, are displayed in Fig. 3. At low
concentration (2.5 ꢂ 10 M) both dyes exhibit a unique and broad
band, with a maximum at 506 and 493 nm respectively, which are
assigned to ICT band as a result of charge transfer from the donor
group (triphenylamine) to the acceptor group (cianoacetic acid) via
excited-state intramolecular charge transfer between the donor
and acceptor in the dyes. Large Stokes shift could help to reduce
self-quenching and measurement error by excitation light and
scattered light [18].
ꢀ
6
The two dyes showed red-shifted absorption profile (Fig. 3a)
when adsorbed on TiO
in solution, being this more pronounce in the case of PER-EF-2
38 nm). The observed bathochromic shift is attributed to the for-
mation of J-aggregates of the dyes at the TiO surface, which is
2
as compared to the corresponding spectra
the
p-conjugated linker. However at higher concentrations
ꢀ5
(
2.5 ꢂ 10 M) PER-EF-1 shows a new broad band in the longer
(
wavelength range (above 700 nm), which indicates the formation
of dye aggregates. In the case of PER-EF-2, this is not observed since
dye aggregation is suppressed by the presence of hexyl chain in the
triarylamine donor group. The molar absorption coefficients of
2
opposite to the blue-shift observed for most organic dyes because
of partial deprotonation of the carboxylic acid unit due to the dye-
TiO2 interaction [16,17]. The fluorescence spectra for dyes in
toluene were obtained by excitation at 450 nm. Both dyes exhibit a
broad structure less emission peaking at 695 nm which is
compatible with the proposed assignment.
ꢀ1
ꢀ1
(506 nm) and
PER-EF-1 and PER-EF-2 are 41,000 M
cm
ꢀ1
ꢀ1
4
0,000 M cm (493 nm), respectively. Based on previous re-
ported in literature [5e8] PER-EF-1 and PER-EF-2 present the
highest molar absorption coefficients, indicating that these dyes
have good light-harvesting ability. The six intermediates and two
dyes have large Stokes shifts, which might be attributed to an
Fig. 4 shows a photograph of PER-EF-1 and PER-EF-2 in toluene
solution (Fig. 4a) and adsorbed on TiO film (Fig. 4b).
2
Fig. 3. (a) Normalized absorption spectra of PER-EF-1 (black) and PER-EF-2 (gray) at low and high concentration in toluene solution (2.5 ꢂ 10 M and 2.5 ꢂ 10ꢀ5 M) and adsorbed
ꢀ6
films; (b) Normalized emission spectra of PER-EF-1 (black line) and PER-EF-2 (gray line) in toluene (2.5 ꢂ 10ꢀ M,
5
l
exc ¼ 450 nm).
on TiO
2

ꢀ
304
E. Torres et al. / Dyes and Pigments 112 (2015) 298e304
procedures liable for scale-up. PER-EF-1 and PER-EF-2 display
intense absorption in the visible range. In addition, these dyes
exhibit high molar absorption coefficients which make them good
light harvesting materials for ss-DSCs because of their ability to
absorb light effectively in very thin films. The performance char-
acterization of these dyes in DSCs is underway and will be reported
in a future article.
Acknowledgements
This work was supported by National Funds through FCT e
Foundation for Science and Technology under the Project PTDC/
CTM-CER/111590/2009 and E. Torres was supported by a doctoral
grant from FCT (SFRH/BD/73999/2010).
Fig. 5. Cyclic voltammograms recorded for the dyes PER-EF-1 (black line) and PER-EF-
2
(gray line) in DMF solutions with TBAPF
6
(0.1 M) as the electrolyte; scan rate:
ꢀ
1
þ
50 mV s . All voltammograms were referenced to internal ferrocene (Fc/Fc ).
References
Table 3
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PER-EF-2
600
557
2.07
2.22
ꢀ5.88
ꢀ5.81
ꢀ3.81
ꢀ3.59
a
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[
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a, 5b, 7a, 7b, 8a and 8b result from fits with a sum of three ex-
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6
The potential was externally calibrated by ferrocene/ferrocenium
þ
couple (Fc/Fc ) and then was calculated versus NHE electrode. The
[
13] Parreira P, Torres E, Nunes C, Nunes de Carvalho C, Lavareda G, Amaral A, et al.
HOMO energy level was calculated using the following equation:
2
Dye-sensitized 1D anatase tio nanorods for turnable efficient photodetection
in the visible range. Sensors Actuators B 2012;161:901e7.
onset
onset
E
HOMO ¼ ꢀ (EOx þ 4.75) eV, where Eox is the onset oxidation
þ
[
14] Menezes F, Fedorov A, Baleizao C, Valeur B, Berberan-Santos MN. Methods for
the analysis of complex fluorescence decays: sum of Becquerel functions
versus sum of exponentials methods. Appl Fluoresc 2013;1:015002.
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siderations for determining absolute frontier orbital energy levels of conju-
gated polymers for solar cells applications. Adv Mater 2011;23:2367e71.
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organic chromophore for dye-sensitized nanostructure solar cells. Chem
Commum 2006:2245e7.
17] Thomas KRJ, Hsu YC, Lin JT, Lee KM, Ho KC, Lai CH, et al. 2,3-Disubstituted
thiophene-based organic dyes for solar cells. Chem Mater 2008;20:1830e40.
18] Zhang Z, Achilefu S. Synthesis and evaluation of polyhydroxylated near-
infrared carbocyanine molecular probes. Org Lett 2004;6:2067e70.
19] Planells M, Pellej aꢁ L, Clifford JN, Pastore M, Angelis F, L oꢀ pez N, et al. Energy
potential versus Ag/Ag [15]. The dyes displayed irreversible waves
and the HOMO and LUMO level (Table 3) were found to be ꢀ5.88
and ꢀ3.81 eV for PER-EF-1 and -5.81 and ꢀ3.59 eV for PER-EF-2,
respectively.
Both dyes exhibit LUMO levels more positive than the conduc-
[
tion band of TiO
2
(ꢀ4.26 eV) [9,19] and hence should in theory have
enough driving force for effective injection, when used as sensi-
tizers in DSCs.
[
[
[
4
. Conclusion
levels, charge injection, charge recombination and dye regeneration dynamics
In summary, we have successfully designed and synthesized
for donor-acceptor
2
p-conjugated organic dyes in mesoscopic TiO sensitized
new perylene dyes following a synthetic strategy and purification
solar cells. Energy Environ Sci 2011;4:1820e9.