Tunable, strongly-donating perylene photosensitizers for dye-sensitized solar cells

Article abstract of DOI:10.1039/c1jm10993f

Broadly absorbing perylene dyes bearing three-triarylamine groups were synthesized via Sonogashira coupling. The triarylamine moieties allowed further installation of electron donating ability, to enable tuning of the oxidation potential and optical band gap. With introducing more electron-donating groups into the three-triarylamine moieties the device performance was improved. The trend can be rationalized by the distribution of the electron density in the HOMO of the perylene moiety as well as the light-harvesting property of the perylene dyes.

Full text of DOI:10.1039/c1jm10993f

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PAPER
Tunable, strongly-donating perylene photosensitizers for dye-sensitized solar
cells†
abc
Simon Mathewab and Hiroshi Imahori
*
Received 7th March 2011, Accepted 10th March 2011
DOI: 10.1039/c1jm10993f
Broadly absorbing perylene dyes bearing three-triarylamine groups were synthesized via Sonogashira
coupling. The triarylamine moieties allowed further installation of electron donating ability, to enable
tuning of the oxidation potential and optical band gap. With introducing more electron-donating
groups into the three-triarylamine moieties the device performance was improved. The trend can be
rationalized by the distribution of the electron density in the HOMO of the perylene moiety as well as
the light-harvesting property of the perylene dyes.
(1 ppb) of the rare earth metal used. The quest to develop fully
Introduction
organic dyes or inexpensive metal complexes has revealed the
Dye-sensitized solar cells (DSSCs) have been actively pursued as
possibility of many types of dye to achieve high performance
an economical solar energy conversion technology since their
when used in a DSSC.5 Of these dyes, perylene photosensitizers
inception over two decades ago.1 The composition of a typical
have been explored as possible alternatives due to their chemical
DSSC is a photoanode composed of conductive glass (e.g. fluo-
and thermal stability, low cost and excellent light-harvesting
rine-doped tin oxide, FTO, Fig. 1) to which a layer of an inex-
ability.6 The physical and chemical features of perylene dyes
pensive, inorganic n-type semiconductor is applied. In the case of
make them ideal candidates for use as photosensitizers in DSSCs.
the most DSSCs, nanocrystalline TiO2 is used but the versatility
The anhydride moiety, used to anchor the perylene to the TiO2,
of the cell allows the use of other n-type semiconductors
can also be incorporated into the dye structure with great ease.
(e.g. SnO2, ZnO) and even the use of p-type semiconductors
(NiO).2,3 The nanocrystalline (20 nm) nature of the TiO2 particles
The inclusion of the anhydride functional group is essential, as it
has been shown to promote a strong electronic communication
imparts a large surface area to the semiconductor, a trait which
between the LUMO of the dye and the CB of TiO2.7–9
enables the substrate to adsorb large amounts of photosensitizer.
The result of this enhanced electronic communication is fast
Absorption of light by the dye facilitates the transition from the
electron injection from S* to the CB of the TiO2 and is an
dye ground state (S) to the dye excited singlet state (S*). The dye
essential feature to realizing efficient DSSCs. At the same time,
excited singlet state is able to inject this electron into the
obtaining tunability of the dye properties, such as steric
conduction band (CB) of the TiO2 semiconductor to yield a dye
hindrance, redox potentials and optical properties in a controlled
radical cation (S+). The oxidized dye returns to the neutral,
and simple manner, is vital in synthesizing new and efficient dyes.
ground state through recombination at the cathode with the
ꢀ
injected electron via a redox electrolyte, in many instances Iꢀ/I3
.
The nature of the photosensitizer used to harvest the light is
directly related to the efficiency of the corresponding cell. To
date, the use of organometallic dyes, namely heteroleptic ruthe-
nium complexes has remained the highest performing dye
component used in the DSSC.4 However, this class of dye
possesses some undesirability due to the low natural abundance
aInstitute for Integrated Cell-Material Sciences (iCeMS), Kyoto
University, Nishikyo-ku, Kyoto, 615-8510, Japan
bDepartment of Molecular Engineering, Graduate School of Engineering,
Kyoto University, Nishikyo-ku, Kyoto, 615-8510, Japan
cFukui Institute for Fundamental Chemistry, Kyoto University, Sakyo-ku,
Kyoto, 606-8103, Japan. E-mail: imahori@scl.kyoto-u.ac.jp; Fax: +81 75
383 2571; Tel: +81 75 383 2566
† Electronic supplementary information (ESI) available: Voltammetric
data and 1H and 13C NMR data for H, t-Bu, and OMe. See DOI:
10.1039/c1jm10993f
Fig. 1 Construction and operation of a DSSC.
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One particular feature of great interest in designing dyes for
application in solar cells is the ability to impart charge transfer
(CT) absorption characteristics by inducing partitioning of the
Frontier orbitals. In perylene monoanhydrides, this can be ach-
ieved by simple substitution of an electron-donating group,
usually an amine, on the 9-position of the perylene core. The
perturbation of HOMO and LUMO distribution within the
molecule results in localization of the Frontier orbitals around
the amine and anhydride functionalities respectively.10
tetracarboxylic dianhydride (2, PTCDA) was treated with 2,6-dii-
sopropylaniline/Zn(OAc)2 in quinoline/N,N-dibutylethanolamine
ꢁ
at 230 C to afford N-(2,6-diisopropylphenyl)-3,4-perylene dicar-
boximide (3).13 The monoimide was selectively brominated by
previously reported procedure to give 1,6,9-tribromo-N-(2,6-dii-
sopropylphenyl)perylene-3,4-dicarboximide (1)12,14,15 which was to
be coupled with terminal alkynes 4–6. In contrast to alkyne 4,16
which was synthesized by a previously reported procedure, alkynes
5 and the previously reported 617 were made via Buchwald–Hartwig
coupling of the appropriate para-substituted diphenylamines to
commercially available (4-bromophenylethynyl)trimethylsilane.
Subsequent deprotection of the silyl-protecting group with tetra
n-butylammonium fluoride afforded the required triarylamino-
functionalized terminal alkynes in good overall yields. Alkynes 4–6
were utilized in the aforementioned Sonogashira coupling with 1
using previously reported conditions to afford the trialkynylated
perylene monoimides (7–9) in good yields.18 Alkaline treatment of
the imides (KOH/t-BuOH) afforded the target trifunctionalized
perylene monoanhydrides H, t-Bu, and OMe.
For the purposes of introducing intense CT character into
perylene dyes, it is needed to develop expeditious synthetic
pathways toward the perylene dyes with a strong electron-
donating character that allows the tuning of the maximum
absorption wavelength and oxidation potential, in order to
promote excellent electron injection from the dye excited state
into the CB of the TiO2 and to effect charge recombination
ꢀ
between the oxidized dye and the Iꢀ/I3 redox electrolyte.
There are many reports of perylene dyes synthesised for use in
DSSCs all of which show diverse structural features due to the
regioselective manner that halogenation can be effected onto the
perylene core. 1,6,9-tribromoperylene monoimide (1) is conve-
niently prepared from the commercially available 3,4:9,10-perylene
tetracarboxylic dianhydride (2) in two well-established synthetic
steps.11,12 This synthon has enabled access to 1,6,9-trifunctionalized
perylene monoanhydrides with a large degree of structural diversity
making it possible to develop efficient photosensitizers. Thus, we
chosetoinvestigatethe synthesis, characterization and photovoltaic
properties of 1,6,9-tris(triarylaminoalkynyl)perylene mono-
anhydrides H, t-Bu, and OMe (Fig. 2).
Optical properties
The UV-vis absorption spectra of anhydrides H, t-Bu, and OMe
in CH2Cl2 are given in Fig. 3. All of the absorption spectra
possess similar features. In particular, the broad absorption at
450–750 nm is noteworthy. This absorption is attributed to a CT
absorption of the perylene dye, resulting from the orbital parti-
tioning induced from substitution of a strong donor in the 9-
position of the perylene core. Compared to the perylene photo-
sensitizers previously reported by our group,7 all three dyes in
this work displayed improved absorption properties across the
visible region of the spectrum due to the presence of the CT
absorption. Especially, it is the improvement in the extinction
coefficient that results in improved light-harvesting ability when
the dyes are implemented into photovoltaic devices (vide infra).
Perylene H exhibits a maximum at its CT absorption, appearing
at 574 nm. Within the perylene series presented, it can be seen
that tert-butyl substitution causes a slight red shift in the
absorption maximum of t-Bu, appearing at 588 nm and
demonstrating the ease at which longer wavelength absorption
can be achieved through introduction of electron-donating
substituents at strategic positions. In a similar manner, perylene
OMe, possessing the stronger electron-donating methoxy
groups, experiences a greater red shift to 595 nm but also
a significant increase in extinction coefficient. This significant
increase can be rationalized by the presence of the oxygen atoms
whose lone electron pairs increase the size of the p-system within
the molecule.
The convenience of this synthesis is twofold. Firstly, the
robustness of the Sonogashira coupling protocol to install
alkynyl residues on the perylene ring is fortuitous. Then, the
nature of the alkynyl-functionalized triarylamine allows the
inclusion of electron-donating or sterically demanding groups by
simply utilizing the appropriate, commercially available N,N-
diphenylamine at the beginning of the synthetic pathway.
Results and discussion
Synthesis of materials
The synthesis of the perylene dyes utilized in this study is outlined in
Scheme
1.
Commercially
available
3,4:9,10-perylene
The fluorescence spectra for compounds H, t-Bu, and OMe in
CH2Cl2 were obtained by excitation at 573 nm and are presented
in Fig. 4. The spectra are featureless and of low energy, remi-
niscent of emission from a CT absorption. The emission
maximum of H appears at 748 nm. The introduction of the tert-
butyl moiety results in a shift of the emission maximum to
790 nm, whereas inclusion of the methoxy group onto the parent
perylene leads to a bathochromic shift to 815 nm. One striking
feature of the fluorescence spectra of this series of perylenes is the
drastic reduction in the emission intensity recorded upon the
inclusion of substituents on the triphenylamine moiety.
Fig. 2 The structure of the perylenes H, t-Bu, and OMe used in this
study.
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Scheme 1 Synthesis of perylene dyes H, t-Bu, and OMe. (a) 2,6-Diisopropylaniline, Zn(OAc)2, quinoline/N,N-dibutylethanolamine, 230 ꢁC, (b) Br2,
CHCl3, reflux, (c) 4–6, Pd(PPh3)4, CuI, THF/N,N-diisopropylethylamine (1 : 1), 80 ꢁC 12 h, and (d) KOH, t-BuOH, reflux 12 h.
The reduction in emission intensity can be rationalized by the
presence of two deactivation processes upon generation of the
excited singlet state of perylene species. One argument is that
a greater degree of vibrational relaxation is experienced by per-
ylenes t-Bu and OMe upon the absorption of light due to the
presence of six additional tert-butyl or methoxy groups, respec-
tively. Due to the presence of these substituents, a reduction in
the fluorescence quantum yield can be expected. Secondly, the
occurrence of a competing intramolecular electron transfer
process can be invoked to rationalize the decrease in emission
intensity experienced by the perylene photosensitizers. This
phenomenon has been observed in perylene bisimides with elec-
tron donating substitutents.19
Fig. 3 UV-Vis absorption spectra of perylenes H (black), t-Bu (red), and
As perylene dyes H, t-Bu, and OMe are to be used as photo-
sensitizers in DSSCs, estimation of the optical HOMO–LUMO
OMe (blue) in CH2Cl2.
Fig. 4 Fluorescence spectra of H (black), t-Bu (red), and OMe (blue) in CH2Cl2 (lex ¼ 573 nm). The absorbance at 573 nm was adjusted to be identical
for comparison.
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gap is essential in drawing conclusions between the optical/elec-
tronic properties of the dye and performance in the corre-
sponding DSSC (vide infra). The data are summarized in Table 1.
Electrochemical properties
The electrochemical properties of the perylene dyes were inves-
tigated by using cyclic voltammetry (CV) and differential pulse
voltammetry (DPV). The redox potentials determined by using
DPV are summarized in Table 2. The DPV measurements reveal
that perylenes H, t-Bu, and OMe possess a reversible first
oxidation potential located at +1.23 to 0.96 V vs. NHE, whereas
reversible first and second reduction potentials located at ꢀ0.53
to ꢀ0.58 vs. NHE (Fig. S1–S3†). Integration of the oxidation
peak obtained from CV relative to the reduction peak of the
perylene moiety (Fig. S1–S3†) reveals that the first oxidation is
a three electron process, and is attributed to the oxidation of the
electron-donating triarylamine groups.
Fig. 5 DPV curves of H (black), t-Bu (red), OMe (blue) (vs. NHE)
obtained in CH2Cl2 containing 0.1 M Bu4NPF6.
presented in Fig. 6. The calculated energies for the Frontier
orbitals and the HOMO–LUMO gap are listed in Table 3.
Two essential features are observed from the calculation of the
Frontier orbitals of the dyes. Firstly, the HOMOs of the perylene
dyes are located at the perylene core and the triarylamine
substituents and the LUMOs at the perylene core and the
anhydride moiety. Secondly, the trend in the calculated band gap
energy corresponds well with the trends observed by electro-
chemical and optical measurements (vide supra).
An interesting feature that electrochemical analysis revealed is
the tunability of the oxidation potential as a function of the
substitution on the triarylamino group. Perylene H, possessing
no substitution, resulted in Eox ¼ +1.23 V (vs. NHE) whereas
perylene t-Bu, functionalized with tert-butyl groups, possessed
Eox ¼ +1.09 V (vs. NHE) and through the inclusion of strongly
electron-donating methoxy groups, perylene OMe exhibits
Eox ¼ +0.96 V (vs. NHE) (Fig. 5). Thus, by simply changing the
substitution on the triarylamino groups, the oxidation potential
of the dye can be easily tuned in order to engineer dyes that, upon
oxidation, favour fast regeneration by Iꢀ/I3ꢀ (+0.5 V vs. NHE) in
the electrolyte. Moreover, all of the dyes possess excited state
potentials more negative than the conduction band of TiO2
(ꢀ0.5 V vs. NHE),20 making electron injection from the dye into
the CB of the TiO2 thermodynamically possible.
Photovoltaic performance
DSSCs were fabricated using dyes H, t-Bu, and OMe by
immersing the TiO2 electrodes with a double layer structure
consisting of 12 mm thickness with 20 nm sized TiO2 nano-
particles and 4 mm thickness with 400 nm sized TiO2 nano-
particles into THF solutions of the perylenes (0.2 mM). Initially,
power conversion efficiency (h) was evaluated as a function of
immersion time of the electrode in the dye solution. Therefore,
immersion times of 1, 3, 6, 12, 24 hours were investigated, the
result of which is presented in Fig. 7, with an additional
Molecular orbital calculations
To gain further insight into the geometric, electronic and optical
properties of perylenes H, t-Bu, and OMe were subjected to ab
initio calculations, using hybrid density functional theory (DFT)
with the 3-21G basis set. The optimized structures of the
respective molecules and, most importantly the distribution of
Frontier orbital throughout the molecule were calculated and are
Table 1 Absorption/fluorescence maxima and optical band gaps for H,
t-Bu, and OMe
Dye
labs/nm
lem/nm
E0ꢀ0/eV
H
t-Bu
OMe
574
588
595
748
790
815
1.84
1.82
1.81
Fig. 6 Frontier orbitals of perylenes H, t-Bu, and OMe optimized using
B3LYP/3-21G level of theory.
Table 2 Redox potentials as determined by DPV (vs. NHE) obtained in
CH2Cl2 containing 0.1 M Bu4NPF6
Table 3 Molecular orbital energy levels for perylenes H, t-Bu, and OMe
Dye
Eox/V
Ered/V
Eox ꢀ Ered/eV
Eox*/V
Dye
EHOMO/eV
ELUMO/eV
Bandgap/eV
H
t-Bu
OMe
+1.23
+1.09
+0.96
ꢀ0.53
ꢀ0.58
ꢀ0.58
1.76
1.67
1.54
ꢀ0.61
ꢀ0.73
ꢀ0.85
H
t-Bu
OMe
ꢀ4.96
ꢀ4.82
ꢀ4.68
ꢀ2.95
ꢀ2.86
ꢀ2.78
2.01
1.96
1.90
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immersion time of 48 hours for dye t-Bu included in the plot (not
shown).
for OMe is non-intuitive, in that the dye saturation adsorption is
reached at 12 hours, but the corresponding cell experiences
a slight decline in the efficiency at and beyond this immersion
time. The amounts of dye adsorbed per unit area are rather
similar for perylenes H and t-Bu, are significantly larger than that
for OMe. The reasoning for this was attributed to a combination
of two differences between H compared to t-Bu and OMe.
Firstly, the increased molecular size of perylenes t-Bu and OMe
compared to H would result in slower binding due to steric
limitations during the adsorption process. Secondly, the slight
perturbations in the Frontier orbitals (as visualized in the ab
initio calculations in Fig. 6) of t-Bu and OMe located about the
anhydride moiety upon introduction of the electron donating
substituents to the triphenylamine moieties is suspected to affect
the anchoring of the dye. However, the observation of OMe to
achieve a lower power conversion efficiency due to the prolonged
Perylene H shows steady increases in the h as a result of pro-
longing the immersion time to a maximum of 2.1% after 6 hours.
The introduction of tert-butyl groups in t-Bu results in a slow
increase in
h over prolonged immersion times reaching
a maximum of 2.1% at 24 hours immersion. The difference in the
optimal immersion time between H and t-Bu is attributed to
lower electron density of the anchoring group in the LUMO of
t-Bu, causing slower binding of t-Bu to the TiO2 substrate
(vide infra). The best performance achieved was for dye OMe
using an immersion time of 6 hours to yield an h value of 2.9%.
However, if the substrate was allowed longer immersion times
than this, a sharp drop in cell performance was observed. To
further access the binding behaviour of the dyes as a function of
time, the amount of dye adsorbed onto the TiO2 substrate was
assessed. This was achieved calculating the amount of dye on
dye-adsorbed TiO2 substrates (1 cm2). The amount of dye was
calculated, assuming no difference between the molar absorption
coefficient in solution and on the substrate, and was monitored
as a function of immersion time (Fig. 8).
20
immersion time suggests either aggregation of dye on the TiO2
or an alteration to a more tilted binding geometry of the dye to
the TiO2,21 both of which have been demonstrated to have
profound negative effects on the corresponding cell performance.
Fig. 9 depicts the photocurrent–voltage characteristics of the
TiO2/dye cells under respective conditions giving maximum
performance for each dye (Table 4). Introduction of the tert-
butyl groups in t-Bu results in a slight increase of both the JSC
(5.6 mA cmꢀ2) and the VOC (0.60 V) when compared to the same
values for H where JSC ¼ 5.0 mA cmꢀ2 and VOC ¼ 0.58 V.
Presumably the origin of the larger improvement in photovoltaic
parameters in t-Bu is a result of reduced electron density of the
perylene moiety close to the anchoring group in the HOMO of
t-Bu achieved by electron-donating alkyl substitution on the
triphenylamine donor moieties.22 The introduction of the
stronger electron donating methoxy groups in OMe leads to
the further increase of both the VOC (VOC ¼ 0.61 V) and JSC
(JSC ¼ 6.5 mA cmꢀ2). This can be correlated well to the further
decrease in electron density of the perylene moiety close to the
anchoring group in the HOMO of OMe achieved by more elec-
tron-donating alkoxy substitution on the triphenylamine donor
moieties as well as improved light-harvesting property due to the
larger molar absorption coefficient of OMe.21
The plot in Fig. 8 shows that the 90% saturation for the final
adsorbed dye for H is achieved after 6 hour immersion time,
whereas the sterically demanding t-Bu requires at least 24 hours
for the majority of the dye to adsorb. This adsorption behaviour
parallels the optimal adsorption times for maximum power
conversion efficiency for these perylene dyes. However, the case
Fig. 7 Profiles of h vs. immersion time for perylenes H (black), t-Bu
(red), and OMe (blue).
Fig. 9 Photocurrent–voltage characteristics of perylenes H (black), t-Bu
(red), and OMe (blue). Conditions: electrolyte 0.1 M LiI, 0.05 M I2, 0.6 M
2,3-dimethyl-1-propyl imidazolium iodide and 0.5 M 4-tert-butylpyridine
in CH3CN; input power AM 1.5 under simulated solar light 100 mW
Fig. 8 The plot of adsorbed dye (mol cmꢀ2) vs. immersion time (h) for
perylenes H (black), t-Bu (red), and OMe (blue).
cmꢀ2
.
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Table 4 Photovoltaic data under optimised conditions
performed with UltraPure Silica Gel (230-400 mesh, SiliCycle)
1
and Silica gel 60 F254 (Merck), respectively. H NMR spectra
Dye
JSC/mA cmꢀ2
VOC/V
ff
h (%)
Immersion time/h
were acquired on a JEOL EX-400 (400 MHz) or a JEOL AL-300
(300 MHz) spectrometer. UV-vis absorption spectra were
measured using a Perkin-Elmer Lambda 900 UV/VIS/NIR
Spectrophotometer. Fluorescence FT-IR Spectra were recorded
on a JASCO FT/IR-470 plus spectrometer, using a KBr pellet.
High-resolution mass spectra were acquired using FAB and EI.
Elemental analyses were performed at Kyoto University. Elec-
trochemistry was performed on an ALS 630a electrochemical
analyzer using CH2Cl2 containing 0.1 M tetrabutylammonium
hexafluorophosphate (Bu4NPF6) as the supporting electrolyte. A
glassy carbon electrode (3 mm diameter), Ag/AgNO3 (0.01 M in
CH3CN) and a Pt wire counter electrode were used in all cases.
Ferrocene/ferrocenium (Fc/Fc+, +0.642 V vs. NHE) or deca-
methylferrocene (Me10Cp/Me10Cp+, +0.076 V vs. NHE) was
used as the internal reference for the samples to enable conver-
sion of obtained values to the NHE scale. DFT calculations were
performed using Gaussian 03 and orbitals were visualized using
the Molstudio 3.0 package.
H
t-Bu
OMe
5.0
5.6
6.5
0.58
0.60
0.61
0.74
0.74
0.72
2.1
2.1
2.9
6
24
6
Photocurrent action spectra were obtained on the optimized
cells and they follow the absorption features of the correspond-
ing perylenes adsorbed on the electrode, indicating that the
perylene dye is responsible for photocurrent generation. Per-
ylenes H and t-Bu displayed IPCE spectra of comparable breadth
but the maximum IPCE of t-Bu (42% at 515nm) eclipsed that of
H (34% at 510 nm). Perylene OMe recorded the highest IPCE
value (43% at 515 nm) as well as the broadest IPCE spectrum,
with the absorption ceasing at ꢂ700 nm. The presence of the
electron donating groups on t-Bu and OMe contributed posi-
tively to the improvement of the higher IPCE in the corre-
sponding devices, compared to H. This matches the trend that
the driving force increases with introducing more electron-
donating groups into the amine moieties (Table 2), leading to
more efficient electron injection from the perylene excited singlet
state to the CB of the TiO2.23 Furthermore, it demonstrates how
the favourable tuning of dye properties (lmax and Eox) enables
OMe to overcome the intense quenching of fluorescence (as
observed by steady-state fluorescence spectra) to undergo effi-
cient electron injection into the TiO2 substrate, resulting in
improved light harvesting ability. Thus, both tuning Eox as well
as extension of the p-electron system facilitated favourable
electron injection and longer wavelength absorption maximum
observed in the IPCE spectrum respectively, resulting in the
higher efficiency observed by this device (Fig. 10).
Dye sensitized solar cells
UV-vis absorption measurements of the perylenes adsorbed on
TiO2 were performed using TiO2 (20 nm) with a thickness of
12 mm without a light scattering layer.
Preparation of TiO2 electrodes and the fabrication of sealed
DSSCs were performed using the previously reported literature
method.24,25 Nanocrystalline TiO2 paste (20 nm CCIC:
PST18NR, JGC-CCIC) was used as the transparent semi-
conducting substrate on the photoanode for dye adsorption and
submicrocrystalline TiO2 (400 nm particles, CCIC:PST400C,
JGC-CCIC) was used to provide a light scattering layer. The
working electrode was prepared by cleaning FTO glass (Solar,
4 mm thick, 10 U per Sheet, Nippon Sheet Glass) with a detergent
solution (distilled water) in an ultrasonic bath for 10 minutes,
rinsing with distilled water, ethanol and air drying. The electrode
was subjected to UV–O3 irradiation (18 min), immersion into
a solution of freshly prepared 40 mM TiCl4(aq) at 70 ꢁC for
30 min, washing with distilled water, ethanol and air drying.
Nanocrystalline TiO2 was coated onto the FTO by screen
printing (area 0.25 cm2, 5 mm ꢃ 5 mm), followed by standing in
a clean box for a few minutes and dried at 125 ꢁC for 6 min,
repeating to attain a final thickness of 12 mm. The thickness of the
films was determined using a surface profiler (SURFCOM 130A,
ACCRETECH). A layer of 4 mm submicrocrystalline TiO2 paste
was deposited in the same fashion as the nanocryꢁstalline layer.
The electrode was heated under an airflow at 325 C for 5 min,
375 ꢁC for 5 min, 450 ꢁC for 15 min and 500 ꢁC for 15 min. The
electrode was then subjected to immersion into 40 mM TiCl4(aq)
at 70 ꢁC for 30 min before rinsing with distilled water and ethanol
and air drying. Prior to immersion into dye solutions, the elec-
Experimental
General
All chemicals were of reagent grade quality, purchased and used
without further purification. Solvents were purchased from
Wako Chemicals (Japan) and used as received. Anhydrous THF
was distilled from a benzophenone ketyl/sodium still. Column
chromatography and thin-layer chromatography (TLC) were
ꢁ
trodes were sintered at 500 ꢁC, cooled to 70 C and immersed
into the dye solution and incubated at 25 ꢁC in the dark for the
prescribed times.
The counter electrode was prepared by drilling a small hole in
FTO glass (Solar, 1 mm thick, 10 U per Sheet, Nippon Sheet
Glass), rinsing with distilled water and ethanol before treatment
with 0.1 M HCl/2-propanol in an ultrasonic bath for 5 minutes
Fig. 10 IPCE spectra of perylenes H (black), t-Bu (red), and OMe
(blue).
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(removal of iron contamination). Counter electrodes were
washed with water and ethanol followed by ultrasonication in
on silica eluting with CH2Cl2 to give 5 as a white solid (922 mg,
94%); mp 138–140 ꢁC; dH (300 MHz; CD2Cl2) 1.31 (18 H, s, 2 ꢃ
Ar-C(CH3)3), 6.89 (2 H, d, Ar-H, J 8.7), 7.01 (4 H, d, 2 ꢃ Ar-H,
J 8.7), 7.28 (2 H, d, Ar-H, J 8.7), 7.31 (4 H, d, 2 ꢃ Ar-H, J 8.7); dC
(75 MHz; CD2Cl2) 31.5, 34.6, 76.1, 84.4, 113.8, 121.0, 125.3,
126.7, 133.2, 144.7, 147.3, 149.2; IR (KBr cell): nmax/cmꢀ1 3295
(alkyne C-H), 3037 (Ar-H), 2961 (CH3), 2901, 2866 (Ar-H), 2104
(alkyne C-C), 1598, 1504 (Ar-H), 1322, 1284 (C-N), 831 (para-
substituted Ar); m/z (EI) 381.2464 (M+. C20H31N requires
381.2457).
ꢁ
acetone and heating in air at 400 C for 15 min. Platinum was
deposited by coating the electrode with a solution of H2PtCl6
ꢁ
(2 mg in 1 mL EtOH) twice and heating in air at 400 C for 15
minutes.
The sandwich cell was prepared by assembling the photoanode
and the counter electrode together, using a hot-melt ionomer film
ꢁ
(Surlyn, DuPont) at 130 C. Surlyn was also used to cover the
hole drilled on the back of the counter electrode, to allow
vacuum backfilling of the cell with the electrolyte. The drilled
hole was finally covered with another piece of Surlyn film and
a cover glass (0.13–0.17 mm thick). The exposed FTO on the cell
was roughened with sandpaper to allow the application of solder
to the edge of the FTO electrodes. The electrolyte used was
composed of 0.1 M LiI, 0.05 M I2, 0.6 M 2,3-dimethyl-1-propyl
imadazolium iodide and 0.5 M 4-tert-butylpyridine in CH3CN.
Photocurrent action spectra were obtained using the PEC-S20
(Peccell Technologies) action spectrum measurement apparatus.
Photocurrent–voltage (I–V) characteristics were measured using
a solar simulator (PEC-L10, Peccell Technologies) with simu-
lated sunlight of AM 1.5 (100 mW cmꢀ2) using a mask of black
plastic tape to limit the amount of scattering light to TiO2 film
area.
Bis(4-methoxyphenyl)aminephenylacetylene-TMS protected (6-
TMS). Bis(4-methoxyphenyl)amine (500 mg, 2.18 mmol),
(4-bromophenylethynyl)trimethylsilane (610 mg, 2.4 mmol),
NaOt-Bu (262 mg, 2.73 mmol), Pd2(dba)3 (20 mg, 0.022 mmol),
and P(t-Bu)3 (10% solution in hexane, 66 mL, 0.033 mmol) in
toluene (13 mL) were degassed with argon for 10 minutes then
heated at 80 ꢁC for 12 hours. The solvents were evaporated and
the residue subjected to column chromatography on silica using
Hexane/CHCl3 (1 : 3) as the eluant to give 6-TMS as a yellow
solid (660 mg, 75%); dH (400 MHz; CD2Cl2) 0.24 (9 H, s, Si
(CH3)3), 3.78 (6 H, s, 2 ꢃ Ar-OCH3), 6.77 (2 H, d, Ar-H, J 8.8),
6.86 (4 H, d, 2 ꢃ Ar-H, J 8.8), 7.06 (4 H, d, 2 ꢃ Ar-H, J 8.8), 7.23
(2 H, d, Ar-H, J 8.8); dC (100 MHz; CD2Cl2) ꢀ0.2, 55.6, 92.3,
106.0, 113.7, 115.0, 118.7, 127.5, 132.8, 140.2, 149.3, 156.8; m/z
(EI) 401.1815 (M+. C25H27NO2Si requires 401.1811).
Synthesis
All chemicals were purchased and used without purification.
Synthesis of N-(2,6-diisopropylphenyl)-3,4-perylene dicarbox-
imide (3),13 1,6,9-tribromo-N-(2,6-diisopropylphenyl)perylene-
3,4-dicarboximide (1),12 and 4-ethynyltriphenylamine (4)16 was
as per literature methods.
Bis(4-methoxyphenyl)aminephenylacetylene
(6).
ꢁ
6-TMS
(555 mg, 1.38 mmol) in CH2Cl2 was cooled to 0 C and TBAF
(1 M in THF, 2.67 mmol, 2.67 mL)ꢁwas added dropwise. The
solution was stirred for 2 hours at 0 C and the solvents evapo-
rated. The residue was subjected to column chromatography on
silica eluting with CH2Cl2 to give 6 as a yellow solid (432 mg,
95%); dH (400 MHz; CD2Cl2) 3.01 (1 H, s, ArCC-H), 3.76 (6 H, s,
2 ꢃ Ar-OCH3), 6.76 (2 H, d, Ar-H, J 8.8), 6.83 (4 H, d, 2 ꢃ Ar-H,
J 8.8), 7.05 (4 H, d, 2 ꢃ Ar-H, J 8.8), 7.23 (2 H, d, Ar-H, J 8.8); dC
(100 MHz; CD2Cl2) 55.8, 75.8, 84.5, 112.6, 115.2, 118.9, 127.7,
133.2, 140.3, 149.7, 156.9; m/z (EI) 329.1414 (M+. C22H19NO2
requires 329.1416).
Synthetic methods
Bis(4-tert-butylphenyl)aminephenylacetylene-TMS protected
(5-TMS). Bis(4-tert-butylphenyl)amine (1.01 g, 3.59 mmol),
(4-bromophenylethynyl)trimethylsilane (1.00 g, 3.95 mmol),
NaOt-Bu (431 mg, 4.48 mmol), Pd2(dba)3 (33 mg, 0.0359 mmol),
and P(t-Bu)3 (10% in hexane, 0.0592 mmol, 120 mL) in toluene
(25 mL) were degassed for 10 minutes with Ar then heated at
80 ꢁC for 12 hours. The solvent was evaporated and the residue
subjected to column chromatography on silica using CH2Cl2 to
give the desired product as a white solid (1.24 g, 72%); mp 134–
136 ꢁC; dH (300 MHz; CD2Cl2) 1.31 (18 H, s, 2 ꢃ t-Bu), 6.91
(2 H, d, Ar-H, J 6.6), 7.00 (4 H, d, 2 ꢃ Ar-H, J 6.3), 7.25 (4 H, d,
2 ꢃ Ar-H, J 6.3), 7.27 (2 H, d, J 6.6, Ar-H); dC (75 MHz; CD2Cl2)
ꢀ0.2, 31.4, 34.5, 92.7, 105.8, 114.9, 120.9, 125.1, 126.5, 132.9,
144.6, 147.1, 148.8; IR (KBr cell): nmax/cmꢀ1 3035 (Ar-H), 2960
(CH3), 2902, 2867 (Ar-H), 2154 (alkyne C-C), 1598, 1503 (Ar-H),
1322, 1282 (C-N), 1249 (Si-CH3), 865, 840 (para-substituted Ar);
m/z (EI) 453.2849 (M+. C31H39NSi requires 453.2852).
Triphenylamine perylene imide (7). 1 (200 mg, 0.279 mmol),
CuI (27 mg, 0.15 mmol), Pd(PPh3)4 (32 mg, 0.028 mol) in THF
(10 mL) and N,N-diisopropylethylamine (10 mL) were degassed
with Ar for 30 min. 4 (245 mg, 0.91 mmol) was added and the
ꢁ
mixture stirred for 15 hours at 80 C. The reaction mixture was
diluted with HCl (2 N, 80 mL), extracted with CH2Cl2 (2 ꢃ
50 mL), the organics dried (MgSO4) and evaporated. The dark
solid was purified by column chromatography on silica, eluting
with CHCl3/Hexane (2 : 1) to remove the starting material then
CHCl3 to elute 7 as a black solid (308 mg, 85%); mp > 300 ꢁC; dH
(400 MHz; CD2Cl2) 1.16 (12 H, d, 2 ꢃ CH(CH3)2, J 6.8), 2.78
(2 H, quintet, 2 ꢃ CH(CH3)2, J 6.8), 7.02 (2 H, d, Ar-H, J 8.8),
7.03 (2 H, d, Ar-H, J 8.8), 7.04 (2 H, d, Ar-H, J 8.8), 7.08–7.15
(18 H, m, Ar-H), 7.28–7.36 (16 H, m, Ar-H), 7.48 (4 H, 2 ꢃ d, 2 ꢃ
Ar-H, J 8.8), 7.52 (2 H, d, Ar-H, J 8.8), 7.79 (1 H, t, Pery-H,
J 8.3), 7.88 (1 H, d, Pery-H, J 8.3), 8.60 (1 H, d, Pery-H, J 8.3),
8.79 (1 H, s, Pery-H), 8.80 (1 H, s, Pery-H), 9.84 (1 H, d, Pery-H,
J 8.3), 9.96 (1 H, d, Pery-H, J 8.3); dC (100 MHz; CD2Cl2) 24.2,
29.6, 87.5, 91.2, 91.3, 96.8, 97.1, 99.1, 115.2, 115.3, 115.4, 118.9
Bis(4-tert-butylphenyl)aminephenylacetylene
(5).
5-TMS
ꢁ
(1.24 g, 2.57 mmol) in CH2Cl2 (15 mL) was cooled to 0 C and
TBAF (1 M in THF, 3.75 mmol, 3.75 mL) was aꢁdded in
a dropwise manner. The resulting solution stirred at 0 C for 1
hour then at room temperature overnight. The solvents were
evaporated and the residue purified by column chromatography
7172 | J. Mater. Chem., 2011, 21, 7166–7174
This journal is ª The Royal Society of Chemistry 2011

View Article Online
(2 ꢃ s), 120.4 (2 ꢃ s), 121.9 (2 ꢃ s), 122.0, 124.4, 124.5, 124.9,
125.8, 125.9, 126.9, 127.8, 128.0, 128.3, 128.8 (2 ꢃ s), 129.0,
129.2, 129.9 (3 ꢃ s), 130.2, 131.7, 133.1, 133.2, 133.2 (2 ꢃ s),
136.6, 137.0, 138.1, 138.2, 146.5, 147.3, 147.4, 149.1, 149.2 (2 ꢃ
s), 163.9 (2 ꢃ s); IR (KBr cell): nmax/cmꢀ1 3035 (Ar-H), 2861 (Ar-
H), 2184 (alkyne C-C), 1705, 1667 (imide C-O), 1590, 1506 (Ar-
H), 1313, 1280 (C-N), 753, 695 (Ar-H); m/z (FAB) 1282.5211
(M+. C94H66N4O2 requires 1282.5186).
2868 (Ar-H), 2186 (alkyne C-C), 1709, 1670 (imide C-O), 1597,
1507 (Ar-H), 1320, 1297 (C-N), 829 (para-substituted Ar); m/z
(FAB) 1618.8905 (M+. C118H114N4O2 requires 1618.8942).
4-tert-Butyltriphenylamine perylene anhydride (t-Bu).
8
(300 mg, 0.234 mmol) and KOH (1.32 g, 23.4 mmol) in t-BuOH
(70 mL) were heated at reflux for 4 hours. The reaction mixture
was cooled to room temperature and poured into HCl (2 N,
240 mL). The organics were extracted with DCM (3 ꢃ 50 mL),
the organics dried (MgSO4) and evaporated. The dark solid was
subjected to column chromatography on silica eluting with
CHCl3 and precipitated from CHCl3/MeOH to afford t-Bu as
a black solid. (208 mg, 61%); mp > 300 ꢁC; (found C, 87.7; H, 6.7;
N, 2.9; C106H97N3O3 requires C, 87.2; H, 6.7; N, 2.9%); dH
(400 MHz; CD2Cl2) 1.31 (18 H, s, C(CH3)3), 1.32 (18 H, s, C
(CH3)3), 1.33 (18 H, s, C(CH3)3), 6.80 (2 H, d, Ar-H, J 8.8), 6.84
(2 H, d, Ar-H, J 8.8), 6.88 (2 H, d, Ar-H, J 8.8), 7.00–7.07
(14 H, m, Ar-H), 7.13–7.20 (4 H, m, Ar-H and Pery-H), 7.27–
7.31 (14 H, m, Ar-H), 7.92 (1 H, s, Pery-H), 7.97 (1 H, d, Pery-H,
J 8.0), 8.00 (1 H, s, Pery-H), 9.11 (1 H, d, Pery-H, J 8.0), 9.31
(1 H, d, Pery-H, J 8.0); dC (100 MHz; CD2Cl2) 31.6, 31.7, 34.7,
87.2, 90.7, 90.8, 98.9, 99.0, 113.9, 114.0, 114.5, 115.0, 115.1,
118.1, 118.2, 120.6, 120.7, 120.9, 125.2, 125.5, 125.6, 126.2, 126.8,
127.1, 127.2, 127.7, 127.9 (2 ꢃ s), 128.2, 128.4, 129.5, 130.0,
132.3, 132.8, 132.9, 133.1, 135.8, 136.3, 139.0, 139.2, 144.5
(2 ꢃ s), 144.6, 147.3, 147.4, 149.2, 149.4, 159.7; IR (KBr cell):
nmax/cmꢀ1 3035 (Ar-H), 2960 (CH3), 2902, 2867 (Ar-H), 2185
(alkyne C-C), 1770, 1740 (imide C-O), 1597, 1506 (Ar-H), 1322,
1268 (C-N), 829 (para-substituted Ar); m/z (FAB) 1459.7513
(M+. C106H97N3O3 requires 1459.7530).
Triphenylamine perylene anhydride (H).
7
(310 mg,
0.276 mmol), KOH (1.5 g, 27.6 mmol) and t-BuOH (70 mL) were
combined and the mixture heated at reflux for 3 hours. Upon
cooling to room temperature, HCl (2 N, 250 mL) was added and
the mixture stirred overnight. The organics were extracted with
CH2Cl2 (3 ꢃ 50 mL), dried (MgSO4) and the solvent evaporated.
The black solid was purified by column chromatography on silica
eluting with CHCl3. Precipitation of the product from CH2Cl2/
MeOH washing with MeOH and drying on high vacuum affor-
ꢁ
ded H as a black solid (223 mg, 72%); mp > 300 C; (found C,
87.2; H, 4.6; N, 3.7; C82H49N3O3 requires C, 87.6; H, 4.4; N,
3.7%); dH (400 MHz; CD2Cl2) 6.90 (2 H, d, Ar-H, J 8.8), 6.93
(2 H, d, Ar-H, J 8.3), 6.94 (2 H, d, Ar-H, J 8.8), 7.04–7.12 (20 H,
m, Ar-H), 7.18 (1 H, d, Pery-H, J 8.3), 7.25–7.36 (16 H, m, Ar-H),
7.38 (1 H, t, Pery-H, J 8.3), 8.06 (1 H, s, Pery-H), 8.13 (1 H, s,
Pery-H), 8.15 (1 H, d, Pery-H, J 8.3), 9.26 (1 H, d, Pery-H, J 8.3),
9.46 (1 H, d, Pery-H, J 8.3); dC (100 MHz; CD2Cl2) 77.9, 87.3,
90.7, 90.8, 98.6, 98.9, 99.5, 114.6, 114.7, 114.8 (2 ꢃ s), 115.4,
117.6, 117.7, 121.5, 121.6, 121.7, 124.4 (2 ꢃ s), 125.0, 125.8,
125.9, 126.7, 126.9, 127.3, 127.4, 127.6, 127.9, 128.2, 129.4, 129.6,
129.9, 132.1, 132.7, 132.9, 133.1, 135.3, 135.9, 138.9, 139.1, 147.2,
147.3, 147.4, 148.9, 149.1, 159.4; IR (KBr cell): nmax/cmꢀ1 3035
(Ar-H), 2923, 2852 (Ar-H), 2183 (alkyne C-C), 1769, 134
(anhydride C-O), 1587, 1507 (Ar-H), 1268 (C-N), 753, 694
(Ar-H); m/z (FAB) 1123.3762 (M+. C82H49N3O3 requires
1123.3774).
4-Methoxytriphenylamine perylene imide (9). 1 (137 mg,
0.191 mmol), CuI (18 mg, 0.095 mmol), Pd(PPh3)4 (22 mg,
0.019 mmol) in THF (6.9 mL) and N,N-diisopropylethylamine
(6.9 mL) were degassed with Ar for 10 min. 6 (233 mg, 0.707
mmol) was added and the mixture stirred for 15 hours at 80 ꢁC.
The reaction mixture was diluted with HCl (2 N, 100 mL),
extracted with CH2Cl2 (3 ꢃ 50 mL), the organics dried (MgSO4)
and evaporated. The dark solid was purified by column chro-
matography on silica, eluting with CHCl3/Hexane (2 : 1) to
remove the starting material thꢁen CHCl3 to elute 9 as a black
solid (255 mg, 91%); mp > 300 C; dH (400 MHz; CD2Cl2) 1.15
(12 H, d, CH(CH3)2, J 6.8), 2.77 (2 H, quintet, 2 ꢃ CH CH
(CH3)2, J 6.8), 3.78 (12 H, s, 2 ꢃ -OCH3), 3.79 (6 H, s, -OCH3),
6.82–6.89 (18 H, m, Ar-H), 7.10 (12 H, d, Ar-H, J 8.0), 7.33–
7.40 (6 H, m, Ar-H), 7.43 (2 H, d, Ar-H, J 8.0), 7.49 (1 H, t, Ar-
H, J 8.0), 7.75 (1 H, t, Pery-H, J 8.0), 7.83 (1 H, d, Pery-H, J
8.0), 8.58 (1 H, d, Pery-H, J 8.0), 8.75 (1 H, s, Pery-H), 8.76
(1 H, s, Pery-H), 9.83 (1 H, d, Pery-H, J 8.0), 9.95 (1 H, d, Pery-
H, J 8.0); dC (100 MHz; CD2Cl2) 24.1, 29.6, 55.8, 77.9, 87.2,
91.0, 97.4, 97.6, 99.6, 113.1 (2 ꢃ s), 113.3, 115.3, 118.8 (2 ꢃ s),
118.9, 119.0, 119.1, 120.2, 120.3, 124.4, 125.1, 126.7, 127.7,
127.8, 127.9 (2 ꢃ s), 128.6, 128.0, 129.2, 129.3, 129.8, 129.9,
130.0, 131.7, 132.9, 133.0, 133.2, 136.4, 136.7, 137.9, 138.0,
140.1, 140.2, 146.5, 149.9, 150.1 (2 ꢃ s), 157.2 (2 ꢃ s), 163.9; IR
(KBr cell): nmax/cmꢀ1 3038 (Ar-H), 2996, 2959 (CH3), 2923,
2903, 2832 (Ar-H), 2184 (alkyne C-C), 1705, 1667 (imide C-O),
1599, 1504 (Ar-H), 1242 (C-N), 827 (para-substituted Ar); m/z
(FAB) 1462.5859 (M+. C100H78N4O8 requires 1462.5820).
4-tert-Butyltriphenylamine perylene imide (8). 1 (200 mg,
0.279 mmol), CuI (27 mg), Pd(PPh3)4 (38 mg) in THF (10 mL)
and N,N-diisopropylethylamine (10 mL) were degassed with Ar
for 20 min. 5 (401 mg, 1.05 mmol) was added and the mixture
ꢁ
stirred for 15 hours at 80 C. The reaction mixture was diluted
with HCl (2 N, 80 mL), extracted with CH2Cl2 (3 ꢃ 50 mL), the
organics dried (MgSO4) and evaporated. The dark solid was
purified by column chromatography on silica, eluting with
CHCl3/Hexane (2 : 1) to remove the starting material then
CHCl3 to elute 8 as a black solid (346 mg, 77%); mp > 300 ꢁC; dH
(400 MHz; CD2Cl2) 1.14 (12 H, d, 2 ꢃ CH(CH3)2, J 6.8), 1.32
(36 H, s, 2 ꢃ C(CH3)3), 1.33 (18 H, s, C(CH3)3), 2.76 (2 H,
quintet, 2 ꢃ CH CH(CH3)2, J 6.8), 6.97–7.00 (6 H, m, Ar-H),
7.08 (12 H, d, Ar-H, J 8.5), 7.28–7.35 (14 H, m, Ar-H), 7.45–7.52
(7 H, m, Ar-H), 7.84 (1 H, t, Pery-H, J 8.0), 7.93 (1 H, d, Pery-H,
J 8.0), 8.65 (1 H, d, Pery-H, J 8.0), 8.82 (1 H, s, Pery-H), 8.84
(1 H, s, Pery-H), 9.93 (1 H, d, Pery-H, J 8.0), 10.02 (1 H, d, Pery-
H, J 8.0); dC (75 MHz; CD2Cl2) 31.6, 34.7, 87.4, 91.1, 97.1, 97.3,
99.4, 114.2 (2 ꢃ s), 114.4, 119.0, 120.3 (2 ꢃ s), 120.7, 120.9, 124.5,
125.1, 125.5, 125.6, 126.8, 127.8, 127.9, 128.0, 128.7, 129.0, 129.2,
129.2, 129.8, 129.9, 130.1, 131.7, 132.9, 133.0, 133.2, 135.6, 136.5,
136.8, 138.0, 138.1, 144.5, 144.6, 146.5, 147.6, 147.6, 149.4, 149.5,
149.6, 163.9; IR (KBr cell): nmax/cmꢀ1 3035 (Ar-H), 2961 (CH3),
This journal is ª The Royal Society of Chemistry 2011
J. Mater. Chem., 2011, 21, 7166–7174 | 7173

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2 R. Jose, V. Thavasi and S. Ramakrishna, J. Am. Ceram. Soc., 2009,
92, 289–301.
3 F. Odobel, L. Le Pleux, Y. Pellegrin and E. Blart, Acc. Chem. Res.,
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4 C. Y. Chen, M. Wang, J. Y. Li, N. Pootrakulchote, L. Alibabaei,
4-Methoxytriphenylamine perylene anhydride (OMe).
9
(167 mg, 0.114 mmol) and KOH (640 mg, 11.4 mmol) in t-BuOH
(35 mL) were heated at reflux for 8 hours. The reaction mixture
was cooled and poured into HCl (2 N, 240 mL) the mixture was
extracted with CH2Cl2 (3 ꢃ 50 mL), dried (MgSO4) and evapo-
rated. The remaining solids were purified by column chroma-
tography on silica CHCl3 and precipitated from CHCl3/MeOH
to afford OMe as a black solid (74 mg, 50%); mp > 300 ꢁC;
(found C, 79.8; H, 4.9; N, 3.2; C88H61N3O9 requires C, 81.0; H,
4.7; N, 3.2%); dH (400 MHz; CD2Cl2) 3.78 (6 H, s, O-CH3), 3.79
(6 H, s, O-CH3), 3.80 (6 H, s, O-CH3), 6.74 (2 H, d, Ar-H, J 8.8),
6.77 (2 H, d, Ar-H, J 8.8), 6.81 (2 H, d, Ar-H, J 8.8), 6.82–6.88
(12 H, m, Ar-H), 7.03–7.10 (14 H, m, Ar-H and Pery-H), 7.17
(2 H, d, Ar-H, J 8.8), 7.26 (2 H, d, Ar-H, J 8.8), 7.31 (2 H, d, Ar-
H, J 8.8), 8.03 (1 H, s, Pery-H), 8.08 (1 H, d, Pery-H, J 8.0), 8.09
(1 H, s, Pery-H), 9.24 (1 H, d, Pery-H, J 8.0), 9.44 (1 H, d, Pery-
H, J 8.0); dC (100 MHz; CD2Cl2) 55.9, 87.1, 90.7, 98.9, 99.1, 99.9,
125.1, 126.2, 127.1 (2 ꢃ s), 127.3, 127.8, 127.9, 128.2, 128.4,
128.8, 129.4, 130.0, 132.4, 132.8, 132.9, 133.2, 135. 8, 136.3,
139.0, 139.1, 140.1 (2 ꢃ s), 140.2, 149.7, 149.8 (2 ꢃ s), 149.9,
157.1 (2 ꢃ s), 159.9; IR (KBr cell): nmax/cmꢀ1 3037 (Ar-H), 2995,
2948 (CH3), 2929, 2903, 2832 (Ar-H), 2183 (alkyne C-C), 1766,
1734 (anhydride C-O), 1599, 1503 (Ar-H), 1241 (C-N), 826 (para-
substituted Ar); m/z (FAB) 1303.4447 (M+. C100H78N4O8
requires 1303.4408).
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17 J. H. Lin, A. Elangovan and T. I. Ho, J. Org. Chem., 2005, 70, 7397–
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Conclusions
We have successfully prepared novel perylene dyes bearing
strong electron-donating, three-triarylamine groups for the first
time. With introducing more electron-donating group into the
three-triarylamine moieties the device performance was
improved considerably. The improvement can be explained by
the distribution of the electron density in the HOMO of the
perylene moiety, the electron injection efficiency, and the light-
harvesting property of the perylene dyes. Such fundamental
information will be useful for the molecular design of novel dyes
exhibiting high device performance.
18 Z. An, S. A. Odom, R. F. Kelley, C. Huang, X. Zhang, S. Barlow,
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19 J. Huang, Y. Wu, H. Fu, X. Zhan, J. Yao, S. Barlow and
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20 H. Imahori, S. Hayashi, H. Hayashi, A. Oguro, S. Eu, T. Umeyama
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21 H. Imahori, S. Kang, H. Hayashi, M. Haruta, H. Kurata, S. Isoda,
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ꢀ
P. Chabera, A. P. Yartsev and V. Sundstrom, J. Phys. Chem. A,
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€
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22 J. N. Clifford, E. Palomares, M. K. Nazeeruddin, M. Gratzel,
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Acknowledgements
23 K. Hara, T. Sato, R. Katoh, A. Furube, Y. Ohga, A. Shnpo, S. Suga,
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S.M. is grateful to the Japanese Society for the Promotion of
Science (JSPS) for a JSPS Postdoctoral Fellowship for Foreign
Researchers.
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24 S. Ito, T. N. Murakami, P. Comte, P. Liska, C. Gratzel,
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25 H. Imahori, Y. Matsubara, H. Iijima, T. Umeyama, Y. Matano,
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This journal is ª The Royal Society of Chemistry 2011