Trans-disubstituted benzodiazaporphyrin: A promising hybrid dye between porphyrin and phthalocyanine for application in dye-sensitized solar cells

Article abstract of DOI:10.1016/j.jphotochem.2016.07.026

We have synthesized a zinc benzodiazaporphyrin trans-substituted by a di-(3,5-tert-butyl)phenyl and 4-phenyl carboxylic acid groups (coded CROSSDAP). This new dye has been characterized by UV–vis absorption and emission spectroscopy, electrochemical measu

Full text of DOI:10.1016/j.jphotochem.2016.07.026

Accepted Manuscript
Title: Trans-disubstituted benzodiazaporphyrin: a promising
hybrid dye between porphyrin and phthalocyanine for
application in Dye-Sensitized Solar Cells
´
Author: Dmitry S. Andrianov Yoann Farre Kathy J. Chen
Julien Warnan Aurelien Planchat Denis Jacquemin Andrei V.
Cheprakov Fabrice Odobel
PII:
S1010-6030(16)30321-5
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.jphotochem.2016.07.026
JPC 10303
To appear in:
Journal of Photochemistry and Photobiology A: Chemistry
Received date:
Revised date:
Accepted date:
2-5-2016
26-7-2016
26-7-2016
´
Please cite this article as: Dmitry S.Andrianov, Yoann Farre, Kathy J.Chen,
Julien Warnan, Aurelien Planchat, Denis Jacquemin, Andrei V.Cheprakov,
Fabrice Odobel, Trans-disubstituted benzodiazaporphyrin: a promising hybrid
dye between porphyrin and phthalocyanine for application in Dye-Sensitized
Solar Cells, Journal of Photochemistry and Photobiology A: Chemistry
http://dx.doi.org/10.1016/j.jphotochem.2016.07.026
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Trans-disubstituted benzodiazaporphyrin: a promising hybrid dye between
porphyrin and phthalocyanine for application in Dye-Sensitized Solar Cells
Dmitry S. Andrianov,a Yoann Farré,b Kathy J. Chen,b Julien Warnan,b Aurelien
Planchat,b Denis Jacquemin,b*c, Andrei V. Cheprakova* and Fabrice Odobel*b
aDepartment of Chemistry, Moscow State University, Moscow, Russia. E-mail:
avchep@elorg.chem.msu.ru
bUniversité LUNAM, Université de Nantes, CNRS, Chimie et Interdisciplinarité:
Synthèse, Analyse, Modélisation (CEISAM), UMR 6230,2 rue de la Houssinière,
44322Nantes cedex 3, France. E-mail: Fabrice.Odobel@univ-nantes.fr
cInstitut Universitaire de France, 1, Rue Descartes, 75005 Paris Cedex 5, France. E-
mail: Denis.Jacquemin@univ-nantes.fr
1

Graphical Abstract
2

Highlights
A simple trans-disubstituted zinc benzodiazaporphyrin is a promising
sensitizer for dye-sensitized solar cells, which opens new opportunities for
tetrapyrrole dyes, especially to harvest the low energy part of visible
spectrum.
3

Abstract:
We have synthesized a zinc benzodiazaporphyrin trans-substituted by a di-(3,5-tert-butyl)phenyl and 4-
phenyl carboxylic acid groups (coded CROSSDAP). This new dye has been characterized by UV-vis
absorption and emission spectroscopy, electrochemical measurements and modeled with TD-DFT
calculations. CROSSDAP exhibits interesting absorption properties which resemble those of a zinc
phthalocyanine; that is an intense Q-band localized at 685 nm. CROSSDAP was used as sensitizer on
nanocrystalline TiO2 based Dye-Sensitized Solar Cells with iodide/triiodide electrolyte. The solar cell
reaches a 3.37% power conversion efficiency under AM1.5 with an IPCE value over 40% at 680 nm.
CROSSDAP can axially bind an imidazole ligand substituted with a Bodipy dye. When used as additive
in the electrolyte, the latter antenna amplifies the light harvesting efficiency of CROSSDAP in the 450-
550 nm range, a feature which increases the photocurrent up to 8.40 mA/cm2 resulting in a PCE of
3.82%. Overall, these results demonstrate that trans-substituted benzodiazaporphyrins are attractive
new dyes for DSSC, particularly towards the development of efficient sensitizers to harvest the low
energy part of the visible spectrum.
.
Keywords:
Solar cell; Electrochemistry; Density functional theory; Energy Transfer; Antenna, TiO2
Introduction
Dye-sensitized solar cells (DSSCs) represent a clean and sustainable technology for the third
generation of photovoltaics.[1] In this area, ruthenium polypyridine complexes have been the most
efficient sensitizers for several decades, with photoconversion efficiencies in the range of 10-11%.[2-5]
In early 2000, it was discovered that push-pull organic dyes, comprising a -conjugated spacer
functionalized by an electron donating group and an electron withdrawing group, can be particularly
efficient sensitizers in DSSCs. [1, 6-9] More recently, push-pull porphyrin derivatives such as SM315
have attracted a strong interest in DSSCs because cells with such sensitizers have attained a record
efficiency of 13% (Figure 1).[10-12]
4

Figure 1. Structures of efficient porphyrin and phthalocyanine sensitizers used in DSSC.
However, a strong drawback of porphyrin dyes is their weak absorbance both at ca. 450 nm, and above
750 nm where the incoming solar flux is significant. The weak light harvesting efficiency in this region
certainly limits the overall photovoltaic performance of this class of dyes. Phthalocyanines are -
conjugated macrocycles related to porphyrins which have also been thoroughly investigated as
sensitizers in DSSCs, among them PcS20 is a very active one (Figure 1).[12-20] However, the
preparation of trans-disubtituted phthalocyanines is an extremely tedious and challenging synthetic
task,[21, 22] limiting the possibility of developing push-pull phthalocyanines that are appealing dyes for
solar cell applications. Tetrabenzodiazaporphyrins (TBDAPs) can be considered as hybrid dyes between
porphyrins and phthalocyanines since two of the bridging meso-positions are occupied by nitrogen, like
in phthalocyanines, while the two other meso-positions are regular methene moieties, which can carry
substituents.[23] The two interesting and valuable features of benzodiazaporphyrins are, first, the
presence of an intense and long wavelength absorption band similar to phthalocyanines, and second,
the possibility to envision the preparation of push-pull or dipolar systems by functionalization of the two
adjacent carbon meso-positions thanks to the straightforward and efficient synthesis recently reported
by Andrianov, and co-workers.[24] Recently, Imahori and co-workers have reported the photovoltaic
performances of a diazaporphyrin, however the power conversion turned out to be low, which is
attributed to the insufficient electron injection driving force and the formation of aggregates on TiO2.[25]
We found that the simple trans-disubstituted tetrabenzodiazaporphyrin CROSSDAP (Figure 2) performs
quite well in DSSC as compared to similarly substituted porphyrin[26] or phthalocyanine[27] sensitizers.
5

Owing to the recent synthetic methodology to prepare trans-disubstituted benzodiazaporphyrins, the
encouraging photovoltaic performances of CROSSDAP demonstrate the potential of
benzodiazaporphyrins for photovoltaic applications and particularly for DSSCs.
Figure 2. Structures of the dyes studied in this work.
Results and discussion
The synthesis of CROSSDAP is illustrated on Scheme 1. The key transformation leading to the
formation of a diazabenzoporphyrin core with unsymmetrical aryl substituents (8) was achieved by the
cross-dimerization of the corresponding dibenzodipyrrin diacylazides 4 and 7.[24] The parent dipyrrins 4
and 7 were synthesized according to the so-called 4,7-dihydroisoindole method [28, 29] which is a
common and convenient strategy for the synthesis of porphyrins and dipyrrins with a π-extended
aromatic system.[30-37] In the first step, the dihydroisoindole carboxylate tert-butyl ester 1[28] was
reacted with a corresponding aldehyde 2 or 5, followed by oxidation with 2,3-dichloro-5,6-dicyano-1,4-
benzoquinone (DDQ), yielding aryl dibenzodipyrrins 3 and 6 with a circa 75% yield. tert-butyl ester was
selectively cleaved under mild conditions simply by solvolysis in neat TFA, whereas the methyl ester
group in 6 is stable under these conditions. The resulting dipyrrin dicarboxylates are pure enough to be
used in to the following transformations without additional purification. The intermediate dicarboxylate
derivatives were then transformed into the corresponding acylchloride by reaction with SOCl2 and the
latter were subsequently reacted with Bu4NN3 to afford the diacylazides 4 and 7 in 65-70% yields.
Accordingly, acylazides 4 and 7 were synthesized in a multistep one-pot procedure from 3 and 6,
respectively. The large amounts (more than 300 mg) of 4 and 7 can be easily purified by re-precipitation
from acetonitrile, whereas silica gel chromatography is better suited for the small quantities. It is worth
6

noting that the purity of the diacylazides 4 and 7 is critical for the success of the next steps. The
formation of diazabenzoporphyrin 8 was achieved by non-selective cross-dimerization between 4 and 7
in refluxing DMF. This stochastic cross-condensation naturally lead to three different
dizabenzoporphyrins, which were formed with almost the same yield (around 15%). Unsymmetrical
dizabenzoporphyrin 8 has an intermediate polarity among these products and therefore can be easily
isolated by column chromatography. The metallation of 8 by zinc acetate was carried out in DMF under
reflux and lead to 9 almost quantitatively. The metallation progress can be easily monitored by means of
UV-vis spectroscopy by notable changes in the Q-bands region. In the final step, the methyl ester of 9
was hydrolyzed in MeOH/KOH and sufficiently pure CROSSDAP acid was precipitated with HCl.
Compounds 8 and 9 are both well-soluble in dichloromethane and DMF and show no sign of
aggregation in these solvents. The absorption spectra of 9 and CROSSDAP are almost identical
indicating no significant electronic coupling between the aryl groups and the diazabenzoporphyrin core.
Scheme 1.Synthetic route for the preparation of CROSSDAP. Reagents and conditions: a) TsOH,
Bu4NBr, CH2Cl2; b) DDQ, toluene, 2 h, rt., (73% for 3 and 87% for 6); c)neat TFA, 30 min, rt; d) 1.
7

neat SOCl2 min u4NN3, Et3N, MeCN, 1 h, rt., (70% for 4 and 65% for 7); e) DMF,
reflux, 15 min, (15%); f) Zn(OAc)2, DMF, reflux, 30 min, (95%); g) KOH, MeOH, 30 min, rt., (95%).
In agreement with published zinc benzodiazaporphyrins, the absorption spectrum of CROSSDAP
features an intense absorption Q-band at 685 with a high extinction coefficient (=9.3x104 M-1cm-1) along
with another much less intense vibronically resolved Q-band at higher energy (Figure 3).[38], [23] .The
Soret band shows up at 431 nm with a moderate extinction coefficient (=5.8x104 M-1cm-1). Overall, the
spectrum of CROSSDAP resembles more that of a phthalocyanine than that of a porphyrin enabling
thus to harvest low energy photons of visible spectrum. CROSSDAP is also a fluorescent dye exhibiting
a tiny Stoke shift (22 cm-1) suggesting very limited distortion of the first singlet excited state (Figure
3).The 0-0 energy of the first singlet state (E00) is 1.84 eV as measured from the wavelength at the
intersection of the absorption and emission spectra.
1,0
CROSSDAP Absorption
CROSSDA Emission
0,8
0,6
0,4
0,2
0,0
400
450
500
550
600
650
700
Wavelength, nm
Figure 3. Electronic absorption (red line) and emission spectra (blue line) of CROSSDAP recorded in
dimethylformamide.
Cyclic voltammetry measurements were performed to determine the oxidation potential of CROSSDAP
in order to calculate the electron injection and dye regeneration driving forces.CROSSDAP exhibits two
reversible oxidation processes occurring respectively at 0.84 and 1.05 V versus saturated calomel
8

electrode (SCE). The Gibbs free energy enthalpy of the injection (Ginj) and the regeneration (Greg)
reaction can be calculated according to the following equations:
Ginj = EOx1(CROSSDAP+/CROSSDAP) – E00– ECB(TiO2)
-•
Greg = EOx(I2 /I-) - EOx1(D+/D)
where EOx1(CROSSDAP+/CROSSDAP) corresponds to the first oxidation potential of CROSSDAP,
-•
-•
EOx(I2 /I-) to the oxidation potential of I2 /I-[39] and ECB(TiO2)corresponds to the conduction band
potential of TiO2.[1] These calculations support that electron injection (Ginj = -0.30 eV) and dye
regeneration (Greg = - 0.29 eV) processes are both sufficiently exergonic to occur spontaneously.
LUMO+1
LUMO+1
LUMO+1
LUMO
LUMO
LUMO
HOMO
HOMO
HOMO
9

HOMO-1
HOMO-1
HOMO-1
Figure 4. Representation of the frontier molecular orbitals of CROSSDAP (right) and the corresponding,
zinc porphyrin (center) and zinc phthalocyanine (left) substituted with same anchoring group. Isodensity
contour: 0.002 au.
To elucidate the electronic properties of CROSSDAP with respect to those of analogously substituted
zinc porphyrin and zinc phthalocyanine, we have performed DFT and TD-DFT calculations of their
ground and excited state properties, respectively (Figure 4). The optimized structure of CROSSDAP
reveals that the aryl groups are rotated 90.0 degrees to the plane of the diazabenzoporphyrin. The
ground state orbitals of CROSSDAP in Figure 4 allows to confirm that these aryl groups do not
participate significantly in the frontier orbitals, which are in all cases mainly localized within the
macrocycle. This is in contrast with the porphyrin analogue, for which the aryl groups are rotated ca. 65
degrees relative to the macrocycle plane. Consequently, the HOMO and LUMO of the porphyrin exhibit
significantly larger density contributions from the benzoic acid anchoring group, implying a larger
electronic coupling with the semiconductor upon binding, whereas such a contribution is absent in the
frontier molecular orbitals of CROSSDAP (Figure 4).
In terms of their energies levels, shown in Figure 5, the computed gap energy for CROSSDAP (3.66 eV)
falls closely in line with that of the corresponding phthalocyanine (3.63 eV), both of which have more
stabilized gap energies than the porphyrin analogue (4.37 eV). The implications of this are evident in the
10

computed electronic absorption spectra, shown in Figure S1 for all three compounds. In agreement with
the experimental spectra of Figure 3, the visible part of the spectra is dominated by intense absorption
from the Q-band of CROSSDAP (λ=6 6 nm ƒ=0.668), comparable to that of phthalocyanine (653 nm,
ƒ=0.713). In the UV range, the first computed Soret band of CROSSDAP shows up at 374 nm
(ƒ=1.477), slightly higher in energy that of porphyrin (λ=388nm ƒ= 9 3) but lower than phthalocyanine
(λ=320 nm, ƒ= 3). Inspecting the rearrangement of the charge density for the first Soret excited state
in Figure 6 across all three compounds, we observe that the electron density difference for both
porphyrin and CROSSDAP are similarly distributed throughout the macrocycle, again with the notable
difference between the two being the participation of the anchoring group. These computational results
underpin the consensus that the optical features of CROSSDAP lie in between those of porphyrin and
phthalocyanine, possessing both the visible absorption of phthalocyanine and the functionalization
potential of porphyrin.
Figure 5. CAM-B3LYP ground state energy levels of the frontier molecular orbitals of CROSSDAP
compared to zinc porphyrin and phthalocyanine. Red: HOMO and LUMO. Black: HOMO-1, LUMO+1.
11

Figure 6. Density differences between the ground state and the first Soret excited state of
phthalocyanine (left), porphyrin (center), and CROSSDAP (right). Isodensity contour: 0.0004 au.
Nanocrystalline films of TiO2 prepared by screen printing were then coated with CROSSDAP and used
in solar cells with a platinized counter-electrode, sandwiched with an electrolyte based on iodide/triiodide
redox couple solubilized in acetonitrile (see experimental part for details). The metrics of the solar cells
are gathered in Table 1 and the photoaction spectra are shown in Figure 7. The dye was first loaded on
TiO2 in absence of chenodeoxycholic acid (CDCA) in the dying bath, but unexpectedly the performances
were poor owing to the formation of aggregates upon immobilization. The absorption spectra recorded
for thin TiO2 film without scattering layer clearly show the decrease of the aggregates when CDCA was
added in the dye bath. Indeed, in the presence of CDCA the envelope of the large Q-band at 650 nm
narrows and the intensity of the bands at 608 and 636 nm decreases (Figure S2). The optimal
concentration of CDCA was found to be 5 mM, as higher concentrations lead to a lower dye loading and
consequently a lower short-circuit current density (Jsc). It is likely that the introduction of bulky
substituents or alkyl chains on the diazabenzoporphyrin can decrease the propensity of this aromatic -
conjugated macrocycle to aggregate upon immobilization on surface suggesting thus some room to
improvement for next generation of benzodiazaporphyrin sensitizers, if one introduces bulky susbtituents
on the dye.[18] Nevertheless, the obtained performances of CROSSDAP (3.37%) compare very well
with those of simple zinc porphyrin (2.2%)[26] or zinc phthalocyanine (3.52%)[27] as they are in the
same range as those published with similar sensitizer bearing the same benzoic acid anchoring group
(see Table S1). The photoaction spectrum of the cell sensitized with CROSSDAP is shown in Figure 7
and displays a quite significant photoactivity on the Q-band in the 650-700 nm, but with lower Incident
photon-to-current efficiency (IPCE) in the 450-600 nm region owing to intrinsic lower absorbance of the
dye in this spectral window. The highest IPCE value reaches about 40% and we be related to limited
injection quantum yield of CROSSDAP. This is most probably due by the low electronic coupling with
TiO2, as a consequence of the poor extension of the LUMO orbital on the anchoring group (see Figure
4). The introduction of an ethynyl moiety between the meso-position, where the benzoic acid is attached,
could most certainly enhance the injection quantum yield and thereby the IPCE for the future TBDAP
dyes.
12

Figure 7. Photoaction spectra (IPCE as a function of the incident wavelength) of DSSCs sensitized with
CROSSDAP (black) and CROSSDAP+Bodipy (red).
Table 1. Photovoltaic characteristics of the DSSCs recorded under simulated solar spectrum AM 1.5
(100 mW/cm2).
JSC
VOC
FF
PCE
Dye
conditions
(mA/cm²)
(mV)
(%)
(%)
CROSSDAP
0 mM of
CDCA
4.05
518
74,4
1,56
CROSSDAP
5 mM of
CDCA
7.19
620
75,5
3.37
CROSSDAP +
Bodipy
5 mM of
CDCA
8.40
603
75.5
3.82
It is well-known that zinc porphyrins or zinc phthalocyanines can axially bind heteroaromatic amines
such as pyridine and imidazole derivatives, suggesting that benzodiazaporphyrines could also display a
13

similar property.[40-45] We have tested this hypothesis by recording the absorption spectrum of the
simple zinc benzodiazaporphyrine 10 upon titration with N-methylimidazole (Figure 8). The Q-band
region is almost not affected by the ligation of N-methylimidazole onto zinc benzodiazaporphyrine 10,
while the Soret band exhibits an absorbance decrease along with a red-shift with the appearance of a
clear isobestic point at 429 nm (also at 413 and 407 nm) (Figure 8). The enesi−Hildebrand plot[46] of
the absorbance variation at 433 nm as a function of the concentration of the added N-methylimidazole
(Figure S4) permits the calculation of an association constant of 7.14x104 M-1, which is a same range as
those determined between an imidazole derivative and a zinc tetraarylporphyrin (K ≈ x104 M-1)[42] or a
zinc phthalocyanine (K ≈ x104M-1).[47]
0,8
0,7
0,6
0,5
0,4
0,3
370
380
390
400
410
420
430
440
0,2
0,1
0,0
350
400
450
500
550
600
650
700
Wavelength, nm
Figure 8. Spectral change of zinc benzodiazaporphyrine10 upon titration with N-methylimidazole. Inset:
the expanded Soret band region.
In order to enhance the light harvesting efficiency of CROSSDAP, we contemplate the introduction of a
supplementary chromophore acting as an antenna to capture photons in the 450-550 nm window and
transfer the incident photonic energy to CROSSDAP via Forster energy transfer mechanism. A previous
14

study proved that this strategy is quite effective to enhance photocurrent density in DSSC with a zinc
porphyrin sensitizer[48]. To this end, we have investigated the photovoltaic performances of a solar cell
coated with CROSSDAP and in which a Bodipy ligand was added in the iodide/triiodide electrolyte. The
Bodipy molecule used in this study is connected to an imidazole unit and can thus axially bind to
CROSSDAP via a coordination bond with zinc (Figure 2). First, the effective association of the Bodipy
antenna on the immobilized CROSSDAP was confirmed by the observation of the absorption red-shift of
its Soret band as shown on the absorption spectrum of the TiO2 film soaked in a solution of Bodipy
(Figure S5). Interestingly, the photocurrent density of the supramolecular association CROSSDAP-
Bodipy was indeed raised by about 1.2 mA/cm2, enlarging the overall power conversion efficiency of the
cell to 3.82% (Table 1 and Figure S6). The photoaction spectra of the resulting cell clearly shows that
the IPCE in the region 450-550 nm has indeed increased compared to the cell without the Bodipy
(Figure 7). This supports the effective participation of this moiety to electricity generation via energy
transfer since Bodipy itself is a poor sensitizer on TiO2 (PCE≈ 0.22%).[48]
In conclusion, this study demonstrates that trans-substituted TBDAP derivatives represent an attractive
new class of sensitizers for solar cells. Even a simple dye as CROSSDAP is already capable of yielding
a PCE in the same range as those measured with simple zinc porphyrin or zinc phthalocyanine dyes.
Moreover, this class of dye is certainly valuable for harvesting low energy photons of the visible
spectrum due to its intense absorption Q-band in this region. It can be envisioned that introduction of an
ethynyl spacer between the benzodiazaporphyrine and the anchoring group will most probably promote
charge injection. In addition, the presence of a bulky electron donating group such a tris-aryl amine
substituent at the opposite meso-position would enhance the charge transfer character of the electronic
transitions and decrease aggregation, both improving the electron transfer in TiO2 and enhancing the
light harvesting efficiency of the dye. In light of the recent advances in the synthesis of trans-
disubstituted benzodiazaporphyrin, such dyes are now within reach. We are actively exploring these
possibilities in our laboratories.
Experimental part
15

The starting dihydroisoindole tert-butyl ester 1[30] and Bodipy ligand[48] were prepared according to
the procedure described in the literature. FTO conductive glass substrates (F-doped SnO2) were
purchased from Pilkington (TEC8).
The redox potential was measured by cyclic voltammetry using a platinum disc as working electrode, a
platinum rod as auxiliary or counter electrode and a saturated calomel electrode (SCE) as reference
electrode. The scan rate of the potential was fixed to 100mV/s. The analysed solution comprises
0.001 M of CROSSDAP in acetonitrile as solvent and with 0.1 M of Bu4NPF6 as supporting electrolyte.
All density functional theory (DFT) and time-dependent DFT calculations (TD-DFT) were performed with
the Gaussian09 suite.[49] Full optimizations and frequency calculations for all systems were carried out
with the PBE0 functional using tightened thresholds of 10-9 a.u. for the SCF convergence.[50] The 6-
31G(d) atomic basis set was used in conjuction with the LanL2DZ pseudopotential for the zinc.Solvation
effects of acetonitrile were taken into account using the polarizable continuum model (PCM).[51] In a
subsequent step, the optical spectra of the three structures were obtained through TD-DFT using the
nonequilibrium PCM limit , imposing a tightened SCF convergence of at least 10-7 a.u. The thirty lowest-
lying singlet states within the vertical excitation approximation were calculated using the range-
separated CAM-B3LYP hybrid functional and the 6-31+G(d) atomic basis set.[52] For all calculations,
tert-butyl groups have been replaced by methyl groups to reduce the computational overhead without
detriment to the optical properties.
General procedure for preparation of meso-aryl substituted dibenzodipyrromethenes 3 and 6:
Two equivalents of 4,7-dihydroisoindole 1 and one equivalent of a corresponding aryl aldehyde 2 or 5
were dissolved in dry dichloromethane. Para-toluene sulfonic acid (TsOH) (0.1 equivalent) and an
excess of tetrabutylammonium bromide (Bu4NBr) were then added to the solution and stirred for 24 h at
room temperature. Saturated aqueous NaHCO3 was added to the solution and stirred vigorously for 10
min. The organic layer was separated, washed with water, dried and evaporated to afford an orange
solid. The residue was dissolved in toluene, 3 equivalents of 2,3-dichloro-5,6-dicyanoquinone (DDQ)
was added and the solution was stirred for 2 hours at ambient temperature. 10% aqueous solution of
Na2SO3 was added and stirred vigorously for 10 min. Most toluene was removed under reduced
pressure, the residue was diluted by dichloromethane, the organic layer was extracted, washed with
16

water, dried and concentrated in vacuo. The residual solution was applied to a column silica gel column,
eluted with dichloromethane, a deep-violet fraction was collected and the solvent removed under
reduced pressure.
Meso-(3,5-di-tert-butylphenyl)-dibenzodipyrromethene 3:
Were used 0.4 g of 4,7-dihydroisoindole 1, 0.2 g of 3,5-di-tert-butyl benzaldehyde 2 and 0.6 g of DDQ at
the oxidation stage. Yield 0.42 g (73%) of a deep-purple coloured crystalline solid.
M.p. 200°С with decomposition.1Н NMR (CDCl3, 400 MHz): 14.74 (br. s., 1H), 8.15 (d., J = 8.08 Hz, 2H),
7.24 (t., J = 7.43 Hz, 2H), 7.04 (t., J=7.43 Hz, 2H), 6.78 (br. s., 1H), 6.69 (br. s., 2H), 6.39 (d., J=8.08 Hz,
2H), 1.57 (s. 18H) 1.76 (s., 18H).13С NMR (CDCl3): 161.63, 149.71, 147.87, 142.44, 141.33, 138.97,
135.64, 131.33, 125.67, 123.53, 122.70, 122.42, 107.56, 101.73, 81.10, 55.62, 27.82. MALDI-TOF (1,8-
bis-(diphenylamino)-naphthalene, negative ion), m/z 631.54 (M-H)-.
Meso-(4-methoxycarbonylphenyl)-dibenzodipyrromethene 6:
Were used 0.5 g of a 4,7-dihydroisoindole 1, 0.19 g of p-methoxycarbonyl benzaldehyde 5 and 0.75 g of
DDQ at the oxidation stage. Yield 0.58 g (87%) of a deep-purple coloured crystalline solid.
M.p. 147°С with decomposition.1Н NMR (CDCl3, 400 MHz): 14.79 (br. s., 1H), 8.36 (d., J = 8.08 Hz, 2H),
8.16 (d., J = 8.08 Hz, 2H), 7.66 (d., J = 8.08 Hz, 2H), 7.23 (t., J = 7.33 Hz, 2H), 6.97 (t., J=7.33 Hz, 2H),
6.09 (d., J=8.08 Hz, 2H), 4.08 (s., 3H) 1.78 (s., 18H).13С NMR (CDCl3): 166.71, 161.00, 141.38, 139.56,
137.50, 135.48, 133.98, 131.38, 131.14, 130.68, 129.63, 126.93, 125.92, 123.07, 121.73, 82.55, 52.54,
28.39. MALDI-TOF (1,8-bis-(diphenylamino)-naphthalene, negative ion), m/z 577.86 (M-H)-.
General procedure for preparation of diacylazides 4 and 7:
Dipyrromethene 3 or 6 (0.35 g) was dissolved in trifluoroacetic acid (TFA), stirred for 30 min at room
temperature and TFA was evaporated. The intermediate diacids can be additionally purified by
precipitated from diethyl ether. Excess of thionyl chloride (SOCl2) was added to the solid residue, stirred
for 15 min at 50°С and evaporated under reduced pressure. The solid was then dissolved in dry
acetonitrile, a few drops of Et3N were added and an excess of tetrabutylammonium azide (highly
hygroscopic and toxic!!!) was added to the solution. The mixture was stirred for 1 hour at rt, washed with
water, dried and concentrated in vacuo. The residue was passed through a column with silica, collecting
a blue fraction and evaporated to dryness.
17

Diacylazide 4[24]:
Yield 0.25 g (70%) of a deep-purple coloured crystalline solid.
Diacylazide 7[24]:
Yield 0.25 g (65%) of a deep-purple coloured crystalline solid.
5,15-diaryl-10,20-diazaterabenzoporphrin 8:
An equimolar mixture of azide 7 (0.042 g) and 4 (0.053 g) was dissolved in DCM, evaporated to dryness
and DMF (10-15 mL) was added. The mixture was stirring vigorously and was then rapidly heated using
a heating fan and refluxed in DMF for 15 min. When heated the mixture gains a deep-blue color first
which then turns to red, indicating the decomposition of azide group. In a minute the color begins turning
to green and the formation of small crystals of the products can be seen on a wall of a reaction vessel.
Dichloromethane was then added to the cooled solution and the resulting solution was washed with
water (5x50 mL) and evaporated to dryness. Porphyrinoid 8 was isolated as an intermediate green
fraction by column chromatography on silica using DCM:Hexane 5:2 as an eluent. Yield 0.012 g (15%)
of a deep-green crystalline solid.
M.p >300°C.1H NMR (CDCl3, 400 MHz): 9.69 (d., J=7.58 Hz, 2H), 9.62 (d., J=7.58 Hz, 2H), 8.59 (d.,
J=8.19 Hz, 2H), 8.20 (m., 4H), 8.14 (s., 1H), 8.05 (d., J=7.34 Hz, 2H), 7.93 (t., J=7.34 Hz, 2H), 7.73 (t.,
J=7.82 Hz, 2H), 7.60 (t., J=7.82 Hz, 2H), 7.29 (d., J=6.48 Hz, 2H), 7.00 (d., J=7.95 Hz, 2H), 7.24 (s.,
3H), 1.62 (s., 18H), -1.25 (br. s., 1H), -1.37 (br. s., 1H). 13C NMR has not been recorded because of the
aggregation of 8.
MALDI-TOF (1,8-bis-(diphenylamino)-naphthalene), m/z 834.72 (M-H)-.
CROSSDAP:
The mixture of diaryldiazatetrabenzoporphyrin 8 (0.02 g) with an excess of Zn(OAc)2 dihydrate was
refluxed in DMF for 30 min. The metallation progress was monitored by means of UV-Vis spectroscopy
and the reaction was stopped when the starting material was completely gone. The reaction mixture was
then diluted with dichloromethane, washed with water (3x50 mL), dried and evaporated to dryness. The
residue was dissolved in concentrated solution of potassium hydroxide in methanol and stirred for 30
min at room temperature. The reaction mixture was diluted with water, 0.5M HCl was added dropwise
18

and the precipitate was collected by centrifugation, washed with water and the solid was re-precipitated
from DCM/Methanol mixture to afford deep-green crystalline solid. Yield 0.02 g (95%).
1H NMR (CD3OD/THF-d8, 400 MHz): 9.71 (m. , 4H), 8.72 (br. m., 2H), 8.33 (d., J=7.97 Hz, 2H), 8.18 (t. ,
J=1.75 Hz, 1H), 8.12 (d. , J=1.75 Hz, 2H), 7.97 (t., J=7.20 Hz, 4H), 7.63 (m. , 4H), 7.21 (d., J=8.11 Hz,
4H), 1.55 (s., 18H). 13C NMR has not been recorded because of an insufficient solubility.
MALDI-TOF (1,8-bis-(diphenylamino)-naphthalene, negative ion), m/z 881.6 (M-H)-. HR ESI-MS: calcd
for C55H42N6O2Zn 882.26552, found 882.26392.
Preparation of DSSC and photovoltaic characterization
The FTO substrates were cleaned by successive sonication in soapy water, then an ethanolic solution of
HCl (0.1 M) for 10 minutes, and finally dried in air. TiO2 films were prepared in three steps. A first
treatment is applied by immersion for 30 min in an aqueous TiCl4 solution at 80°C. Three successive
layers of mesoporous TiO2 were then screen printed using a transparent colloidal paste (Dyesol DSL
18NR-T) and a final light scattering layer (Dyesol DSL 18NR-AO) was affixed, with 20-minute long
drying steps at 150°C between each layer. The obtained substrates were then sintered at 450°C,
following a progressive heating ramp (325°C for 5 min, 375°C for 5 min, 450°C for 30 min). A second
TiCl4 treatment was immediately conducted afterwards and the electrodes were fired one last time at
450°C for 30 minutes. Thicknesses (16 µm) were measured by a Sloan Dektak 3 profilometer. The
prepared TiO2 electrodes were soaked while still hot (ca. 80°C) in a 0.2 mM solution of CROSSDAP and
chenodeoxycholic acid (5 mM) in a 1:1 mixture (v:v) of toluene and ethanol. After one night of dyeing at
room temperature, the electrodes were rinsed in ethanol and dried in air, in the dark. Platinum based
counter electrodes were prepared by drop casting two drops of hexachloroplatinic acid in distilled
isopropanol (2 mg per mL) on FTO plates, and subsequent firing at 380°C for 30 minutes. The
photoelectrode and the counter electrode were placed on top of each other and sealed using a thin
transparent film of Surlyn polymer (DuPont, 60 µm) as a spacer. The resulting chamber was filled with
an iodine-based electrolyte (50 mM I2, 0.1 M LiI, 0.6 M 1-ethyl-2,3-dimethylimidazolium iodide and 0.25
M 4-tert-butylpyridine when mentioned, in dry distilled acetonitrile) by vacuum back filling through a
predrilled hole in the counter electrode, and the photovoltaic device was sealed afterwards with Surlyn
and a cover glass. The cell had an active area of 0.25 cm2. Photovoltaic measurements were performed
19

with a calibrated AM 1.5 artificial solar light simulator (Oriel) and a Keithley 2400 digital source-meter;
data were collected with a local software designed by Synervia (labview).The photovoltaic
characteristics of the DSSCs were recorded under calibrated Air mass 1.5 spectrum (AM1.5) simulator
at 1000 W/m2.
Acknowledgments
K. J. C. thanks the European Research Council (ERC) for the Ph.D. grant (Marches no. 278845). D. J.
acknowledges both the European Research Council for the starting grant (Marches no. 278845), the
ANR for the salary of Y.F. with the program POSITIF (ANR-12-PRGE-0016-01) and for the salary of
J.W. with the program Asyscol (n°ANR-08-HABISOL-002) and finally the Région des Pays de la Loire
for the LUMOMAT project. We thank the CCIPL (Centre de Calcul Intensif des Pays de la Loire) for the
allocation of computing time. We are thankful to Nadine Szuwarski for the fabrication of TiO2 films on
FTO substrates by screen printing.
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