Ullazine Donor–π bridge-Acceptor Organic Dyes for Dye-Sensitized Solar Cells

Article abstract of DOI:10.1002/chem.201800030

A series of four ullazine-donor based donor–π bridge-acceptor (D–π–A) dyes have been synthesized and compared to a prior ullazine donor-acceptor (D–A) dye as well as a triphenylamine donor with an identical π–bridge and acceptor. The D–π–A ullazine series demonstrates an unusually uniform-in-intensity panchromatic UV/Vis absorption spectrum throughout the visible region. This is in part due to the introduction of strong high-energy bands through incorporation of the ullazine building block as shown by computational analysis. The dyes were characterized on TiO₂ films and in DSC devices. Performances of 5.6 % power conversion efficiency were obtained with IPCE onsets reaching 800 nm.

Full text of DOI:10.1002/chem.201800030

A Journal of
Accepted Article
Title: Ullazine Donor-π bridge-Acceptor Organic Dyes for Dye-
Sensitized Solar Cells
Authors: Yanbing Zhang, Hammad Cheema, Louis McNamara, Leigh
Anna Hunt, Nathan Hammer, and Jared Heath Delcamp
This manuscript has been accepted after peer review and appears as an
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of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
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To be cited as: Chem. Eur. J. 10.1002/chem.201800030
Link to VoR: http://dx.doi.org/10.1002/chem.201800030
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10.1002/chem.201800030
Chemistry - A European Journal
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p
Ullazine Donor- bridge-Acceptor Organic Dyes for Dye-
Sensitized Solar Cells
Yanbing Zhang,† Hammad Cheema,† Louis McNamara, Leigh Anna Hunt, Nathan I. Hammer, Jared H.
Delcamp*[ a]
Abstract: A series of 4 ullazine-donor based donor-π bridge-acceptor
(D-π-A) dyes have been synthesized and compared to a prior ullazine
donor-acceptor (D-A) dye as well as a triphenylamine donor with an
identical π-bridge and acceptor. The D-π-A ullazine series
demonstrates an unusually uniform-in-intensity panchromatic UV-Vis
absorption spectrum throughout the visible region. This is in part due
to the introduction of strong high-energy bands through incorporation
of the ullazine building block as shown by computational analysis. The
dyes were characterized on TiO2 films and in DSC devices.
Performances of 5.6% power conversion efficiency were obtained
with IPCE onsets reaching 800 nm.
molecular building blocks such as coumarin, indoline,
triphenylamine, carbazole are employed as donors.[2a, 5] However,
these donors often lack planarization of the nitrogen lone pair with
the dye π-system, conjugation of all p-orbitals on the donor
building block, and the ability to add additional electron donating
groups in conjugation with the dye π-system.[3b] These inherent
challenges have led to the extensive evaluation of various
electron rich π-bridges to compensate for the lack of desired
donor strength. The use of a planarized peri-fused nitrogen
containing building blocks such as ullazine offers a potential
solution to each of these challenges.
Ullazine is a 16 π-electron planar nitrogen containing peri-
fused heterocyclic system which is isoelectronic with pyrene.[3a, 3c,
6]
Ullazine is fully conjugated with a number of substitutable
Introduction
positions for modulating donor strength and tuning dye
morphologies. Ullazine has a charge separated anionic 14 π-
electron aromatic annulene resonance structure around the
periphery which enhances the donation strength of the nitrogen
lone pair by favoring charge separation (Figure 1). This charge-
separated state can be used to promote intramolecular charge
transfer (ICT) at lower energies. Additionally, upon ICT, an
aromatic ring arises on ullazine in the excited-state. This
proaromatic pyridinium ring serves to lower the energy necessary
for ICT by aromatically stabilizing the excited-state.[3b, 3d, 7] These
desirable attributes have been shown to shrink optical band by ~
0.7 eV when compared with an analogous triarylamine donor
based dye.[3c] Ullazine has also known to be stable during redox
processes as is desirable within a solar cell device.[6g] Due to
these properties, ullazine has recently attracted interest in donor-
acceptor dyes and as a donor for porphyrin sensitizers in DSC
devices.[3c, 6a] However, to date ullazine has only been evaluated
once in metal-free donor-π bridge-acceptor sensitizers despite
the potential for robust, panchromatic organic dyes which are
desperately needed in DSCs.[6j]
Dye-sensitized solar cells (DSCs) have attracted increasing
attention since 1991 due to low manufacturing costs, affordable
solar cell materials, easy integration into building materials and
the potential to meet energy production needs.[1] DSCs operate
through light absorption by a sensitizer or dye anchored to a
semiconductor, electron transfer from the excited-state dye to the
semiconductor, collection of the electron by a redox shuttle at a
counter electrode after it has traveled an external circuit, and
return of the electron to the oxidized dye by the redox shuttle. The
sensitizer component of the DSC devices plays a critical role in
controlling light absorption and subsequent electron transfers.
Organic sensitizers based on the conjugated donor-π-acceptor
(D-π-A) framework offer a modular synthesis, high molar
extinction coefficient, and tunable molecular design which has
furnished organic dyes outperforming precious metal containing
sensitizer with power conversion efficiencies (PCEs) of over
13%.[2] Additional improvements to organic sensitizers are
possible by extending the absorption range with precise control of
the sensitizer energy levels. A key functionality needed for many
D-π-A dye systems to extend their absorption spectrum is the
donor building block.[3] Frequently, organic dyes do not have
ground-state oxidation potentials well positioned for minimal
energy loss as a result of the limited availability of stable, strong
electron donating functionality.[4] Typically, phenyl amine organic
favorable charge
separation
multiple subsitution
sites for tunability
1
2
N+
N+
3
4
9
8
N
[a]
Yanbing Zhang,†, Hammad Cheema,† Louis McNamara, Leigh Anna
Hunt, Nathan I. Hammer, Jared H. Delcamp*.
Department of Chemistry and Biochemistry
-
A-
7
5
6
University of Mississippi, University, MS 38677 (MS)
E-mail: delcamp@olemiss.edu
proaromatic
pyridinium
planar
conjugated amine
14 π-electron
anionic annulene
[†]
Authors contributed equally.
Figure 1. Ullazine building block with resonance structures drawn to illustrate
favorable ICT.
Supporting information for this article is given via a link at the end of
the document.
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10.1002/chem.201800030
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Results and Discussion
yield. Formyl groups were installed via Vilsmeyer-Haack reaction
to give the two desired isomers 6b and 7b, which were separated
via silica gel chromatography and carried forward.[3c] The
aldehydes 6a, 6b, 7a and 7b were subjected to modified Corey-
Fuchs
Given the promising known properties of ullazine, a series
of novel D-π-A based ullazine dyes were targeted for synthesis
(Figure 2). This series focused on the incorporation of two
different aryl groups on ullazine with either a para-alkoxy group to
maintain a highly electron rich donor (YZ7 and YZ12) or di-ortho-
alkoxy groups extending over the ullazine π-face to disrupt any
potential π-stacking based aggregation (YZ14 and YZ15). Given
the two strongest donating positions (the 4 and 5 positions) of
ullazine are ortho substituted, an alkyne was chosen to link the
donor to the π-bridge in order to enable access to a fully
planarized π-system conformation. The dyes with identical aryl
substituents vary in position of an alkyne linking group either at
the meta position relative to the nitrogen substituent on the fused
benzene ring (5 position) or at the position adjacent to the aryl
group (4 position). Cyclopentadithiophene (CPDT) was chosen as
an electron rich π-bridge since DSC dyes typically have
considerable energy losses due to lack of electrons with high
enough potential energy in the ground state of the dye to reach
ideal energetics. Additionally, CPDT is a well-established π-
bridge in high efficiency DSCs which allows for a straight forward
comparison of a ullazine-alkyne donor to common amine donors
such as triphenylamines (TPAs).[8] All dyes utilize the ubiquitous
N
For 2a:
LDA, THF
TMS
Br
Br
aryl
N
aryl
H
O
3
N2
aryl
aryl
60% InCl3
toluene
For 2b:
2a
2.0 Br PPh3CHBr2 2b (75%)
6% Pd[P(t-Bu)3]2
4% CuI, 2.4 DIPA,
dioxane
1a
1b
4a
4b (83%)
1.9 KOtBu, THF
aryl
aryl
DMF, DCE
aryl
N
aryl
aryl
aryl
N
N
POCl3
O
5a
5b (29%)
8a (95%)
8b (85%)
or
2.0 Br PPh3CHBr2
1.9 KOtBu, THF
6a
6b (8%)
H
H
OC6H13
or
aryl
aryl
O
aryl
aryl
N
N
a: aryl =
C6H13
O
H
H
b: aryl =
7a
7b (55%)
9a (91%)
9b (33%)
OC6H13
Sonogashira-based Route
6% Pd[P(tBu)3]2
4% CuI, 2.4 DIPA,
dioxane
aryl
aryl
aryl
aryl
N
N
or
H
S
S
H
Br
O
cyanoacrylic acid acceptor.
this manuscript:
8a
8b
9a
H
C6H13
10,
1.2 equiv.
C6H13
HexO
OHex
HexO
OHex
aryl
aryl
aryl
aryl
N
N
YZ7 (97%)
YZ12 (30%)
YZ14 (61%)
3.0
NC
CO2H
N
N
or
7.0 piperidine
CHCl3
S
H
S
S
H
O
O
R
S
YZ12
YZ7
C6H13
C6H13
R
12a (57%)
12b (0%)
11a (97%)
11b (21%)
C6H13
OHex HexO
C6H13
OHex HexO
N
Stille-based Route
N
1.2 BuLi
1.1 SnBu3Cl
16% Pd(PPh3)4
DMF
aryl
aryl
aryl
N
aryl
OHex
OHex
R
N
OHex
OHex
R
THF
H
YZ15
S
S
Br
SnBu3
YZ14
H
O
S
S
13b (100 %)
9b
R=
COOH
CN
C6H13
C6H13
10,
1.2 equiv.
aryl
N
aryl
Hex
Hex Hex = C6H13
3.0
NC
CO2H
prior dyes:
S
YZ15 (31%)
OHex
H
S
7.0 piperidine
CHCl3
HexO
OHex
O
12b (46 %)
C6H13
C6H13
N
Scheme 1. Synthetic route to YZ7, YZ12, YZ14 and YZ15. Yields are only listed
N
for compounds which are novel to this manuscript.
HexO
R
C218
JD21
NC
CO2H
reaction conditions to give desired alkynes 8a, 8b, 9a, and 9b in
high yield except for derivative 9b presumably due to sterics. For
aldehyde precursors to final dyes YZ7, YZ12 and YZ14,
Sonogashira cross couplings with 6-bromo-4,4-dihexyl-4H-
Figure 2. Structure of ullazine-based dyes YZ7, YZ12, YZ14, YZ15, and JD21
as well as TPA dye C218.
The synthesis of YZ7, YZ12, YZ14 and YZ15 is briefly
described here from known intermediates (Scheme 1). The
ullazine heterocycle with two di-ortho-hexyloxyphenyl groups was
synthesized similar to prior analogs.[3c] Briefly, the di-ortho-
hexyloxyphenyl alkyne (2b) was synthesized from the
corresponding aryl aldehyde (1b) via treatment with TMS-
diazomethane and LDA in 91% yield. Alkyne 2b was coupled to
dibromophenyl pyrrole 3 via a Sonogashira reaction in 83% yield.
InCl3 catalyzed cyclization furnished parent ullazine 5b in 29%
cyclopenta[2,1-b:3,4-b']dithiophene-2-carbaldehyde
10
and
intermediates 8a, 8b, or 9a were carried out in low to high yields.
Alkyne 9b, a precursor to YZ15, gave no desired product under
similar conditions, thus an alternative alkyne-stannylation/Stille
coupling route was used to furnish the desired aldehyde 12b in
46% yield. Knoevenagel condensation on the resulting aldehydes
(11a, 11b, 12a, or 12b) furnished the desired dye series.
With the desired dyes in hand, the absorption properties of
the YZ dyes were examined to determine the suitability of these
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10.1002/chem.201800030
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dyes in DSC devices and to better understand the effects of the
ullazine-donor group on ICT. The ullazine-based dyes have a
broad absorbance from 400-700 nm with high molar absorptivities
of (26,000-29,000 M-1cm-1, Figure 3, Table 1). The absorption
spectra of YZ7-YZ15 exhibit an intense peak at around 535 nm,
which is due to the HOMO-LUMO transition of the conjugated
molecule (discussion below). The introduction of the alkyne-
CPDT π-system to give a D-π-A structure lead to a red-shift of the
absorption spectrum relative to D-A ullazine-cyanoacrylic acid
dye JD21 (Figure 2).[3c] Additionally, the D-π-A structure
broadened the absorption spectrum relative to the simple D-A dye
and led to the introduction of a strong high-energy absorption
band. This high-energy transition band is unique to ullazine D-π-
A CPDT bridged dyes as triphenylamine analogues such as C218
only have a single strong absorption band in the visible region.[9]
This is important as the introduction of high-energy bands in the
absorption spectrum has been related to higher performing DSC
favorable with a driving force of 360-550 mV. The ground-state
oxidation potential is similar or higher in energy for these dyes
relative to a triphenylamine analogue (C218), which we attribute
to the strong donation strength of the ullazine donor. The
decrease in overpotential used to regenerate the dye is important
to maximizing DSC device efficiencies, and maintaining high
energy E(S+/S) values with NIR absorbing materials is critical for
efficient solar-to-electric conversion at low energy with TiO2 based
DSC devices. The ullazine aryl substituents were found to have a
significant effect on the dye ground state oxidation potential with
the para-alkyoxyphenyl substituted dyes (YZ7 and YZ12) having
significantly lower energy E(S+/S) values relative to the di-ortho-
alkyoxyphenyl substituted dyes (YZ14 and YZ15). This highlights
that the ullazine-phenyl group plays a key role in tunably tailoring
E(S+/S) values. For favorable electron transfer to TiO2 the dye
excited-state oxidation potential (E(S+/S*)) should be higher in
energy than -0.5 V versus NHE. The dye E(S+/S*) values were
calculated by subtracting the optical band gap (Egopt) found at the
absorption onset from E(S+/S). E(S+/S*) values for the dye series were
found to be between -0.94 and -1.08 V versus NHE, which
provides enough overpotential for injecting an electron from the
photo-excited dye to the TiO2 conduction band.
devices due to
a more uniform absorption of the solar
spectrum.[10] The molar absorptivities of these high energy bands
are comparable to that of the ICT low energy band ranging from
about 15,000-30,000 M-1cm-1. Dyes with strong absorption across
the full visible spectrum are desirable and rare in DSC reports.
Comparing the effects within the proposed series, only a modest
shift (10 nm) of the absorption maximum is observed based on
the substitution position of the alkyne on ullazine with the position
closest to the aryl group (4 position) giving the most red-shifted
values. The ullazine-phenyl group substituent selection had little
effect on the position of the absorption maximum.
In addition to the suitable energetics found for each of the
dyes, well positioned orbitals are required for efficient DSC
devices. The dye lowest unoccupied molecular orbital (LUMO)
Table 1. Optical and electrochemical data for ullazine dyes YZ7, YZ12, YZ14,
YZ15, JD21, and a TPA analogue C218.
opt
dye
λmax (nm)
ε (M-1cm -1
)
E(S+/S) (V)
E(S+/S*) (V) Eg (eV)
YZ7
532
543
537
549
582
550
29,000
28,000
28,000
26,000
28,000
21,000
0.90
0.90
0.71
0.84
1.09
0.89
-0.98
-0.94
-1.08
-1.05
-0.94
-1.06
1.88
1.84
1.79
1.89
2.03
1.95
YZ12
YZ14
YZ15
JD21
C218
*See experimental for detailed energy measurements and calculations.
should be positioned near the TiO2 surface for efficient electron
transfer from the dye to TiO2. Additionally, the highest occupied
molecular orbital (HOMO) should be positioned away from the
TiO2 surface to diminish back electron transfer from TiO2 to the
oxidized dye. Computational studies via density functional theory
(DFT) were carried out to examine the position of the HOMO and
LUMO at the B3LYP and 6-311G(d,p) level (YZ7: Figure 4, YZ12,
YZ14, YZ15: Figure S2). The HOMO of the four ullazine-based
dyes is primarily positioned on the ullazine motif with some
delocalization onto the CPDT π-bridge. This position is ideal for
good separation of the HOMO from the TiO2 surface in space as
the ullazine-donor is at the opposite end of the dyes relative to the
anchor. The LUMO is partially delocalized over the CPDT bridge
and primarily positioned on the acceptor/anchor. The position of
both the HOMO and LUMO suggests these ullazine-based dyes
can perform efficiently in DSC devices, and also suggests the
ullazine-based D-π-A dyes are absorbing light via ICT.
Figure 3. Absorption of YZ7 (black line), YZ12 (red line), YZ14 (blue line),
YZ15 (purple line) measured in CH2Cl2.
Having established a desirable broad absorption spectrum for
use in DSC devices, the dye energy levels were analyzed to
evaluate the thermodynamic suitability of these dyes for DSCs.
Cyclic voltammetry was used to measure the ground-state
oxidation potentials (E(S+/S)) (Table 1). The E(S+/S) values were
measured within a range of 0.71-0.90 V versus NHE which are
significantly more positive than the iodide/triiodide redox shuttle
(0.35 V versus NHE). This indicates neutral dye regeneration is
Time-dependent DFT (TD-DFT) calculations were carried
out to access the orbital contributions to each of the transitions
observed in the absorption spectrum. For the ullazine D-π-A dyes,
TD-DFT indicates the low energy transition band centered at ~530
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nm is dominated by a HOMO to LUMO transition (99%) which
confirm the ICT nature of these dyes (see Figure 4 for orbitals,
see Table S1 for TD-DFT results). The high energy transition
band at ~430 nm which led to a true panchromatic absorption in
the UV-Vis-NIR absorption spectrum is attributed to a
values, incident photon-to-current conversion efficiency (IPCE)
measurements were undertaken. All of the dyes show a broad
IPCE spectrum from 350 nm to approximately 800 nm, however
the height of the IPCE spectrum varies dramatically with peak
IPCE values in the following order YZ14 (35%) < YZ12 (55%) <
Table 2. DSC device parameters for YZ7, YZ12, YZ14 and YZ15.
Dye
Voc/mV
Jsc/ mA cm-2
FF
PCE (%)
YZ7
551
543
477
568
559
11.3
9.6
6.2
10.9
14.1
0.68
0.70
0.70
0.69
0.67
4.4
3.8
2.1
4.4
5.6
YZ12
YZ14
YZ15
YZ7*
See experimental for device details. *Indicates YZ7 optimized device conditions.
YZ15 (65%) = YZ7 (65%). A slight increase in the high-energy
region breadth explains the higher current from YZ7 compared to
YZ15 observed from the IV curve measurements.
The highest performing dye in the series (YZ7) was
subjected to time correlated single photon counting (TCSPC)
excited-state lifetime analysis to evaluate electron injection
efficiency. YZ7 shows excited-state lifetimes shorter than our
instrument response time of (150 ps), both on TiO2 and Al2O3 films,
compared to 1.25 ns in DCM (Figure 6). This is surprising as a
decreasing in excited-state lifetime on TiO2 is commonly thought
to correlate with electron injection; however, electron injection
with in not possible Al2O3 as it is an insulator. Yet, Al2O3 shows a
dramatic decrease in excited-state lifetime. A possible rationale
Figure 4. HOMO, LUMO, HOMO-1, LUMO+1 orbitals for dye YZ7 given
by DFT calculations at the B3LYP/6-311G(d,p) level.
combination of transitions from the HOMO-1 to LUMO (62%) and
HOMO to LUMO+1 (36%). The HOMO-1 and LUMO+1 both have
substantial involvement from the ullazine building block showing
the importance of this building block in adding these strongly
absorbing higher energy bands.
YZ7, YZ12, YZ14 and YZ15 were found to have a
panchromatic solution absorption, properly positioned energy
levels and properly positioned orbitals to perform well in DSC
devices. Thus, devices were fabricated with the ullazine D-π-A
dyes using TiO2 as the semiconductor and iodine/triiodide as the
redox shuttle (Figure 5 and Table 2). Sensitization of TiO2 films is
commonly done with EtOH:THF solutions for many organic dyes;
however, the dyes examined in this report were not fully soluble
at the desired 0.3 mM concentration. The addition of DMF to give
a 4:1:2 (EtOH:THF:DMF) solution gave higher solubility and films
were sensitized from this mixture. Initially the dyes were found to
have PCE values of 2.1-4.4% with YZ7 and YZ15 having the
highest performance according to the equation PCE = (Jsc x Voc
x
FF)/I0 where Jsc is the short circuit current density, Voc is the open
circuit voltage, FF is the fill factor, and I0 is the sun intensity (Table
2, Figure 5). The dyes show similar FF values (0.68-0.70) and
similar Voc values (543-568 mV, except YZ14 with 477 mV). The
Voc values were low in part due to significant LiI needing to be
added to the cell electrolyte to increase Jsc values.
The largest change in dye performance was from the Jsc
parameter, which ranged from 6.2-11.3 mA/cm2. Such a broad
variation in this parameter is somewhat surprising given the
similarity of the dye orbital properties and dye energetics.
Additionally, the two highest Jsc value dyes were YZ7 and YZ15,
which vary structurally the most in the series with a change at the
position of the bridge-acceptor substitution and at the substituents
on the aryl groups. To better understand this large variation in Jsc
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Figure 5. J-V curves (top) and IPCE (bottom) for DSC devices with YZ7, YZ12,
YZ14 and YZ15. *Indicates different dye sensitization solution was used (see
Table 2 for details).
diminishing factor in this series. Evidence for this includes: (1) the
IPCE spectrum onsets at a 100 nm longer wavelength than that
of the DCM solution, (2) the absorption spectrum of the dye on
TiO2 shows the higher energy absorption band as the strongest
transition while the solution absorption spectrum shows the lower
energy absorption band as the strongest, (3) TCSPC studies
show Al2O3 films decrease excited-state lifetimes dramatically
compared to solution measurements, and (4) the addition of a co-
sensitizer (D35) increased the IPCE intensity of YZ7 in a region
of the spectrum where D35 does not absorb which implies
disruption of aggregates (Figure S6). Attempts to diminish
aggregation through addition of CDCA to the dye-deposition
solution only shows a modest change in the dye-TiO2 film
absorption spectrum and no significant enhancement of device
performance. To evaluate the effects of deposition solvent with
the best performing dye, YZ7, a series of solvents were examined
(Table S2, Figure S4). The PCE efficiency varies substantially
with deposition solvent from 3.4-5.6% PCE. The best conditions
were found to be deposition of YZ7 from acetonitrile:tert-
butanol:chlorobenzene (1:1:1.2,v/v/v) with 10:1 CDCA:dye. The
IPCE curve of YZ7 under optimized conditions shows an increase
in percent intensity from 350 nm to 800 nm with a peak value of
75%. The integrated current under the IPCE curve is in good
agreement with the short-circuit current density (Jsc) of 14.1
mA/cm2 measured under AM 1.5 conditions. The measured Jsc
combined with an open-circuit voltage (Voc) of 559 mV and fill
factor (FF) of 0.67 gives the highest power conversion efficiency
(PCE) of the series at 5.6%. These results show that the Ullazine
donor is exceptional at the introduction of desirable dye properties
(panchromatic light absorption, multiple transitions in the UV-Vis
spectrum, and maintaining high energy oxidation potentials);
however, in the solid state the aggregation of these dyes leads to
diminished device performances which must be carefully
optimized to increase IPCE response and device PCE.
for this observation is heavy aggregation of the dye on film
surfaces which diminishes excited-state lifetimes.
To evaluate this hypothesis, solid film UV-Vis absorption
measurements were made for comparison to solution
measurements for YZ7 (Figure 7). Compared to solution
measurements, the strength of the low energy and high energy
transitions are reversed on the film. The results support our
aggregation hypothesis as YZ7 appears to aggregate heavily on
solid films of TiO2. CDCA is commonly used to disrupt
aggregation and at very high loadings (100:1 CDCA:dye), the film
absorption spectrum begins to look more like the solution
spectrum in terms of relative transition intensity. Thus, the shorter
excited state lifetime in the solid-state and the appearance of
aggregation induced absorption may explain the need for higher
LiI loading to achieve a higher injection free energy from the
aggregates to TiO2 by lowering TiO2 conduction band (Table S4).
Figure 6: Time correlated single photon counting graph with YZ7 in DCM
solution, YZ7 on Al2O3, YZ7 on TiO2 and YZ7 on TiO2 with CDCA.
Conclusions
In summary, we have designed and synthesized a series of
metal-free ullazine based D-π-A dyes for the first time. These
dyes were characterized by UV-Vis-NIR absorption spectroscopy,
cyclic voltammetry, and computational analysis, which reveal
suitable characteristics for use in DSC devices. The broad, near
uniform solution absorption intensity from 350-700 nm is
particularly desirable for DSC applications. This dramatic change
in absorption spectrum from the prior reports on D-A ullazine
sensitizers with relatively narrow absorption spectrum response
is encouraging. A PCE of 5.6% was obtained for the highest
performing dye in the series (YZ7) with an IPCE onset of 800 nm.
Given the relatively few metal-free dyes reaching 800 nm in an
IPCE spectrum this dye-design warrants further investigation.
TCSPC studies and film absorption measurements show
substantial aggregation of the dyes on the TiO2 surface. This
strongly suggests the diminishment in IPCE peak value (75% with
a maximum of 90%) is the result of surface aggregation. Future
Figure 7: Normalized UV-Vis absorption of YZ7 in DCM, and TiO2 film
absorption of YZ7 with no CDCA and 100:1 CDCA:dye.
Given the similar energetics and absorption breadths,
aggregation of these dyes on the TiO2 surface is a potential PCE
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10.1002/chem.201800030
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dispersed in a 5 mL solution containing α-terpineol/ethylcellulose (Sigma
aldrich # 46080, 48.0-49.5% (w/w) ethoxyl basis) (ethylcellulose content:
6 wt % of α-terpineol, 280 mg) with 5 ml of acetone. The suspension was
kept under stirring conditions over a period of 2 days, after which the
remaining acetone was removed by rotary evaporator. The α-
terpineol/ethylcellulose mixture was first prepared by completely dissolving
ethylcellulose in α-terpineol in the presence of 5 ml ethanol, once dissolved
excess ethanol was removed by rotary evaporator. The prepared paste
was then used to screen print films with a Sefar screen (54/137–64W)
resulting in 1 µm thick films on TEC 15 FTO glass. Before its use, the TEC
15 was cleaned by submerging in a 0.2% Deconex 21 aqueous solution
and sonicated for 15 minutes at room temperature. The FTO glass was
rinsed with water and sonicated in acetone 10 minutes followed by
sonication in ethanol for 10 minutes. Finally, after paste printing and drying
on a hot plate for 7 minutes at 125oC, substrates were then sintered with
progressive heating from 125oC (5 minute ramp from r.t., 5 minute hold) to
325oC (15 minute ramp from 125oC, 5 minute hold) to 375oC (5 minute
ramp from 325oC, 5 minute hold) to 450oC (5 minute ramp from 375oC, 15
minute hold) to 500oC (5 minute ramp from 450oC, 15 minute hold) using
a programmable furnace (Vulcan® 3-Series Model 3-550). After cooling to
room temperature, the electrodes were dipped in the 0.3 mM dye solution
for 16 hours and used as it is for TCSPC measurements.
dye designs will focus added substituents to the ullazine building
block which are known to dramatically reduce dye aggregation.
Experimental Section
General Information. All commercially obtained reagents were used
as received. 3,9-bis(4-(hexyloxy)phenyl) indolizino[6,5,4,3-ija]quinoline-5-
carbaldehyde (6a) and 3,9-bis(4-(hexyloxy)phenyl)indolizino[6,5,4,3-
ija]quinoline-4-carbaldehyde (7a) were made according to literature.[3c] 6-
bromo-4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-b']dithiophene-2-
carbaldehyde (10) was prepared according to literature procedure.[11] 1-
(2,6-dibromophenyl)-1H-pyrrole (3) was prepared according to literature
procedure.[3c] Thin-layer chromatography (TLC) was conducted with
Sorbtech silica XHL TLC plates and visualized with UV. Flash column
chromatography was performed with Silicycle ultrapure silica gel P60, 40-
63 μm (230-400 mesh). Reverse phase column chromatography was
performed with premium grade C18 silica gel from Sorbent technologies.
1H NMR spectra were recorded on Bruker Avance-300 (300 MHz) and
Bruker Avance DRX-500 (500 MHz) spectrometers and are reported in
ppm using solvent as an internal standard (CDCl3 at 7.28 ppm). NMR data
is reported as s = singlet, d = doublet, t = triplet, q = quartet, p = pentet, m
= multiplet, br = broad, ap = apparent, dd = doublet of doublets, and
coupling constant(s) are in Hertz, followed by integration information.
UV−Vis-NIR spectra were measured with a Cary 5000 instrument. HPLC
measurements were taken using an Agilent 1100A HPLC instrument,
equipped with an Agilent Eclipse Plus C18 column and UV-Vis detector.
90% isopropanol: 10% water was used as the mobile phase at 0.3 ml/min
for all the measurement. HRMS spectra were obtained with a QTOF
HRMS utilizing nanospray ionization. The mass analyzer was set to the
400−2000 Da range. CV data was collected with a CH Instruments
CHI600E instrument.
Photovoltaic Measurements: Current-Voltage curve photovoltaic
characteristics were measured using a 150 W Xenon lamp (Model
SF150B, SCIENCETECH Inc. Class ABA) solar simulator equipped with
an AM 1.5 G filter for a less than 2% spectral mismatch. Prior to each
measurement, the solar simulator output was calibrated with a KG5 filtered
mono-crystalline silicon NREL calibrated reference cell from ABET
Technologies (Model 15150-KG5). The current density-voltage
characteristics of each cell was obtained with a Keithley digital source-
meter (Model 2400). The incident photon-to-current conversion efficiency
was measured with an IPCE instrument manufactured by Dyenamo
comprised of
a 175 W Xenon lamp (CERMAX, Model LX175F),
monochromator (Spectral Products, Model CM110, Czerny-Turner, dual-
grating), filter wheel (Spectral Products, Model AB301T, fitted with filter
AB3044 [440 nm high pass] and filter AB3051 [510 nm high pass]), a
calibrated UV-enhanced silicon photodiode reference, and Dyenamo
issued software.
Electrochemical Characterization. Cyclic voltammetry was
measured with a 0.1 M Bu4NPF6 in CH2Cl2 solution using a glassy carbon
working electrode, platinum reference electrode, and platinum counter
electrode with ferrocene as an internal standard. Values are reported
versus NHE with ferrocene taken as 0.70 V vs NHE. E(S+/S*) is calculated
from the equation E(S+/S*) = E(S+/S) - Egopt. Egopt is estimated from the onset
of the absorption spectrum and converted from nanometers to eV with the
equation: Egopt = 1240/λonset.
Device Fabrication: For the photoanode, TEC 10 glass was
purchased from Hartford Glass. Once cut into 2x2 cm squares, the
substrate was submerged in a 0.2% Deconex 21 aqueous solution and
sonicated for 15 minutes at room temperature. The electrodes were rinsed
with water and sonicated in acetone 10 minutes followed by sonication in
ethanol for 10 minutes. Finally, the electrodes were placed under
UV/ozone for 15 minutes (UV-Ozone Cleaning System, Model ProCleaner
by UVFAB Systems). A compact TiO2 underlayer is then applied by
pretreatment of the substrate submerged in a 40 mM TiCl4 solution in water
(prepared from 99.9% TiCl4 between 0-5oC). The submerged substrates
(conductive side up) were heated for 30 minutes at 70oC. After heating,
the substrates were rinsed first with water then with ethanol. The
photoanode consists of thin TiO2 electrodes comprised of a 10 μm
mesoporous TiO2 layer (particle size, 20 nm, Dyesol, DSL 18NR-T) for
YZ7-YZ15 for devices using the iodine redox shuttle and a 5.0 μm TiO2
scattering layer (particle size, 100 nm, Solaronix R/SP). Both layers were
printed from a Sefar screen (54/137–64W). Between each print, the
substrate was heated for 7 minutes at 125oC and the thickness was
measured with a profilometer (Alpha-Step D-500 KLA Tencor). The
substrate was then sintered with progressive heating from 125oC (5 minute
ramp from r.t., 5 minute hold) to 325oC (15 minute ramp from 125oC, 5
minute hold) to 375oC (5 minute ramp from 325oC, 5 minute hold) to 450oC
(5 minute ramp from 375oC, 15 minute hold) to 500oC (5 minute ramp from
450oC, 15 minute hold) using a programmable furnace (Vulcan® 3-Series
Model 3-550). The cooled sintered photoanode was soaked 30 min at 70oC
in a 40 mM TiCl4 water solution and heated again at 500oC for 30 minutes
prior to sensitization. The complete working electrode was prepared by
Computational Protocol. MM2 energy minimization in ChemBio3D
Ultra (version:13.0.2.3021) was used for the initial energy minimization of
the four dyes. Dihedral angles for the relevant groups were set to values
between the global minimum and the next local minimum on the
conformation energy diagram as calculated by ChemBio3D. Accurate
geometry optimizations were performed sequentially by density functional
theory (DFT) using Guassian09 with the B3LYP functional with the
following basis sets: first 3-21g, second 6-31g (d,p) and finally 6-311g (d,p).
No imaginary frequencies were observed for the optimized geometries.
Time-dependent density functional theory (TD-DFT) computations were
performed with optimized geometries and with the B3LYP functional and
6-311g (d.p) basis set to compute the lowest energy 10 vertical transitions
and oscillator strengths. Orbital images were prepared with Avogadro
1.0.3 with an iso value of 0.30.
Time Correlated Single Photon Counting (TCSPC) Measurements:
Fluorescence lifetime curves were obtained using the 485 nm line of an
LDH series 485B pulsed diode laser (pulse width approx. 100 ps) as the
excitation source and emission was detected using a PicoQuant PDM
series single photon avalanche diode (time resolution approx. 50 ps) and
TimeHarp 260 time correlated single photon counter (25 ps resolution).
The alumina paste was prepared by following the reported procedure with
the following modifications.[12] 167 mg of Al2O3 NPs (particle size ~ 150
mesh, pore size = 58 Å, surface area = 155 m2/g, SigmaAldrich) was
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10.1002/chem.201800030
Chemistry - A European Journal
FULL PAPER
mixture was filtered through a pad of silica gel with 5% ethylacetate:
hexane as eluent to give the crude product after evaporation. Then, the
mixture was purified through silica gel chromatography with 10%
immersing the TiO2 film into the dye solution overnight at room
temperature. The solution is 0.3 mM of dye in different solvent mixtures
(Table S2). For preparing counter electrodes, 2x2 cm squares TEC 7 FTO
glass was drilled using a Dremel-4000 with Dremel 7134 Diamond Taper
Point Bit with FTO side protected by tape. Electrodes were washed with
water followed by a 0.1M HCl in EtOH wash and sonication in acetone bath
for 10 minutes. These washed FTO electrodes were then dried at 400oC
for 15 minutes. A thin layer of Pt-paste (Solaronix, Platisol T/SP) was slot
printed on the FTO, and the printed electrodes were then heated at 450oC
for 10 minutes. After allowing them to cool to room temperature, the
working electrodes were then sealed to the Pt-FTO electrodes with a 25
μm thick hot melt film (Solaronix, “Meltonix”, Surlyn) by heating the system
at 130oC under 0.2 psi pressure for 1 minute. Devices were completed by
filling the electrolyte through the pre-drilled holes in the counter electrodes,
and finally the holes were sealed with a Surlyn circle and a thin glass cover
by heating at 130oC under a pressure of 0.1 psi for 25 seconds. Finally,
soldered contacts were added with a MBR Ultrasonic soldering machine
(model USS-9210) with a solder alloy (Cerasolzer wire diameter 1.6 mm,
item # CS186-150). A circular black mask (active area 0.15 cm2) was
punched from black tape and used in the subsequent photovoltaic studies.
Film absorption was done using TEC 15 glass with 3 μm mesoporous TiO2
film (particle size, 20 nm, Dyesol, DSL 18NR-T), and progressively heated
as described previously.
1
dichloromethane:hexanes to give the final pure product (1.99 g, 29%). H
NMR (500 MHz, CDCl3) d = 7.51-7.42 (m, 3H), 7.37 (t, J = 8.4 Hz, 2H),
7.20 (s, 2H), 6.76 (d, J =8.4 Hz, 4H), 6.60 (s, 2H), 4.10-3.88 (m, 8H), 1.70-
1.49 (m, 8H), 1.32-1.05 (m, 24H), 0.79 (t, J = 6.7 Hz, 12H). 13C NMR (75
MHz, CDCl3) d = 158.3, 132.9, 129.1, 127.0, 126.4, 126.1, 123.0, 121.0,
118.3, 117.2, 105.7, 105.2, 69.0, 31.4, 29.0, 25.6, 22.5, 13.9. IR (neat,
cm−1): 3585, 3174, 3055, 2920, 2855, 2334, 1585, 1452, 1410, 1365, 1244,
1091, 1030, 863. HRMS (ESI) m/z calc’d (positive mode) for C50H65O4NCs
[M+Cs]+ 876.3968, found 876.3904.
3,9-bis(2,6-bis(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinoline-5-
carbaldehyde (6b): To a flame dried, N2 filled round bottom flask was
added 3,9-bis(2,6-bis(hexyloxy)phenyl)-4,4a1-dihydroindolizino[6,5,4,3-
ija]quinolone (5b) (1.90 g, 2.6 mmol, 1.0 equiv.), dichloroethane (8.4 ml,
0.13 M), and anhydrous N,N-dimethylformamide (0.48 ml, 6.24 mmol, 2.4
equiv.). The mixture was stirred at room temperature while POCl3 (0.60 ml,
6.24 mmol, 2.4 equiv.) was added dropwise via syringe. The reaction was
stirred for 5 hours at room temperature to give a red solution. The reaction
mixture was then diluted with
a
50 mL ~1:1 mixture of
dichloromethane:NaOAc (sat. aq.) for 2 hours. The product was purified
with silica chromatography using 10% dichloromethane:hexanes to give
an orange oil (156 mg, 7.8 %) as the major side product. 1H NMR (500
MHz, CDCl3) d = 10.32 (s, 1H), 8.95 (s, 1H), 7.89 (d, J =8.2 Hz, 1H), 7.53
(d, J =8.2 Hz, 1H), 7.44 (s, 1H), 7.41-7.32 (m, 2H), 6.91-6.96 (m, 2H), 6.73
(dd, J =2.9 Hz, J =2.9 Hz, 4H), 4.01-3.82 (m, 8H), 1.55-1.42 (m, 8H), 1.22-
0.98 (m, 24H), 0.77-0.59 (m, 12H). 13C NMR (75 MHz, CDCl3) d = 191.0,
158.1, 158.0, 131.9, 131.2, 130.8, 129.8, 129.6, 129.5, 128.4, 127.9, 126.6,
121.7, 121.2, 119.2, 116.7, 116.5, 115.9, 109.1, 108.7, 105.4, 105.3, 68.9,
68.8, 31.3, 31.3, 28.9, 28.9, 25.5, 25.5, 22.4, 22.4, 13.8, 13.8. IR (neat,
cm−1): 3489, 3284, 3186, 3111, 2922, 2855, 2714, 2337, 1664, 1582, 1453,
1350, 1297, 1245, 1185, 1092, 1028, 940. HRMS (ESI) m/z calc’d (positive
mode) for C51H65O5NCs [M+Cs]+ 904.3917, found 904.3705.
Synthetic Data
2-ethynyl-1,3-bis(hexyloxy)benzene (2b): To a flame dried flask was
added freshly prepared dibromomethyl-triphenylphosphonium bromide3
(38.6 g, 75.3 mmol, 2.02 equiv.) and tetrahydrofuran (377 ml). In one
portion, potassium tert-butoxide (7.93 g, 70.8 mmol, 1.90 equiv.) was
added and the mixture stirred at ambient temperature for 3 minutes. A
solution of 1b1 (11.4 g, 37.3 mmol, 1.0 equiv.) in tetrahydrofuran (63.2 ml)
was added to the reaction mixture via cannula, and the resulting mixture
was stirred at room temperature for 10 minutes. The reaction was cooled
to -78oC and potassium tert-butoxide (20.8 g, 187 mmol, 5.0 equiv.) was
added in one portion following gradual warming to ambient temperature.
After 1.5 hours, the reaction mixture was diluted with dichloromethane and
rinsed with water, dried by Na2SO4 and evaporated. The crude mixture
was purified through silica gel chromatography using 20%
dichloromethane: hexane was the eluent to get clear oil. (8.51 g, 75%). 1H
NMR (500 MHz, CDCl3) d = 7.18 (t, J = 8.4 Hz, 1H), 6.50 (d, J = 8.5 Hz,
2H), 4.03 (t, J = 6.7 Hz, 4H), 3.48 (s, 1H), 1.95-1.70 (m, 4H), 1.60-.142 (m,
4H), 1.42-1.22 (m, 8H), 0.95-0.92 (ap t, 6H). 13C NMR (125 MHz, CDCl3)
d = 161.8, 129.9, 104.5, 101.4, 85.1, 76.3, 68.9, 31.6, 29.1, 25.6, 22.6,
14.0. IR (neat, cm−1): 3324, 2936, 2918, 2852, 1583, 1453, 1391, 1289,
1251, 1092, 894, 771. HRMS (ESI) m/z calc’d (positive mode) for C20H31O2
[M+H]+ 303.2324, found 303.2304.
3,9-bis(2,6-bis(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinoline-4-
carbaldehyde (7b): This material was formed as the major product during
the
formylation
reaction
to
form
3,9-bis(2,6-
bis(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinoline-5-carbaldehyde (6b).
3,9-bis(2,6-bis(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinoline-4-
carbaldehyde (7b) was observed as a slightly lower Rf than 3,9-bis(2,6-
bis(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinoline-5-carbaldehyde (6b)
on TLC with 10% dichloromethane:hexane as eluent. The product was
isolated by silica chromatography with 10% dichloromethane:hexanes to
give a yellow solid (1.09 g, 55%). 1H NMR (500 MHz, CDCl3) d = 9.44 (s,
1H), 7.59-7.50 (m, 3H), 7.46 (s, 1H), 7.64-7.49 (m, 2H), 7.23 (s, 1H), 7.08
(s, 1H), 6.71 (dd, J = 2.7 Hz, 2.7 Hz, 4H), 4.29-3.78 (m, 8H), 1.89-1.41 (m,
8H), 1.41-0.98 (m, 24H), 0.72 (ap t, 12H). 13C NMR (125 MHz, CDCl3) d =
186.6, 158.1, 157.8, 131.9, 130.4, 130.3, 129.7, 128.2, 127.4, 126.7, 126.4,
125.8, 125.2, 124.4, 123.7, 120.9, 120.4, 120.4, 116.4, 115.4, 105.3, 105.3,
105.3, 104.7, 68.7, 68.7, 31.3, 31.2, 29.0, 28.9, 25.6, 25.5, 22.4, 22.4, 13.8,
13.8. IR (neat, cm−1): 3311, 3180, 3057, 2924, 2858, 2335, 1648, 1587,
1523, 1454, 1386, 1290, 1245, 1194, 1093, 908, 879. HRMS (ESI) m/z
calc’d (positive mode) for C51H65O5NCs [M+Cs]+ 904.3917, found
904.3762.
1-(2,6-bis((2,6-bis(hexyloxy)phenyl)ethynyl)phenyl)-1H-pyrrole (4b):
To a flame dried N2 filled flask was added 1-(2,6-dibromophenyl)-1H-
pyrrole (3),[3c] (3.53 g, 11.3 mmol, 1.0 equiv.), 2-ethynyl-1,3-
bis(hexyloxy)benzene (2b) (8.51 g, 28.2 mmol, 2.4 equiv.), CuI (89.4 mg,
0.47 mmol, 0.04 equiv.), Pd[P(tBu)3]2 (359 mg, 0.70 mmol, 0.06 equiv.),
dioxane (23.5 ml), and diisopropylamine (4.21 ml, 28.1 mmol, 2.4 equiv.).
The mixture was stirred at room temperature overnight. The reaction
mixture was then extracted with DCM and H2O. The crude mixture was
purified through silica gel chromatography using 5% ether: hexane as the
eluent to give the pure product (7.22 g, 83%). 1H NMR (500 MHz, CDCl3)
d = 7.65 (d, J =7.7 Hz, 2H), 7.36 (br s, 2H), 7.27 (t, J = 7.7 Hz, 1H), 7.18
(t, J = 8.3 Hz, 2H), 6.51 (d, J = 8.3 Hz, 4H), 6.28 (br s, 2H), 4.02 (t, J = 6.4
5-ethynyl-3,9-bis(4-(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinoline
(8a): To a flame dried flask was added freshly prepared dibromomethyl-
triphenylphosphonium bromide[13] (2.01g, 4.04 mmol, 2.02 equiv.) and
tetrahydrofuran (20.2 ml). In one portion, potassium tert-butoxide (426 mg,
3.80 mmol, 1.90 equiv.) was added and the mixture stirred at ambient
temperature
for
3
minutes.
A
solution
of
3,9-bis(4-
(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinoline-5-carbaldehyde (6a)[3c]
(1.149 g, 2.0 mmol, 1.0 equiv.) in tetrahydrofuran (3.4 ml) was added to
the reaction mixture via cannula, and the resulting mixture was stirred at
room temperature for 10 minutes. The reaction was cooled to negative
78oC and potassium tert-butoxide (426 mg, 3.80 mmol, 5.0 equiv.) was
added in one portion following gradual warming to ambient temperature.
After 1.5 hours, the reaction mixture was diluted with dichloromethane and
rinsed with water, dried by Na2SO4 and evaporated. The crude product
Hz, 8H), 1.95-1.80 (m, 8H), 1.63-1.33 (m, 24H), 0.95-0.90 (ap t, 12H). 13
C
NMR (125 MHz, CDCl3) d = 161.3, 141.4, 133.7, 129.9, 126.0, 122.8, 121.7,
108.2, 104.6, 102.4, 94.3, 87.5, 69.0, 31.8, 29.3, 25.9, 22.8, 14.2. IR (neat,
cm−1): 3098, 3057, 2925, 2860, 1578, 1454, 1383, 1297, 1251, 1093, 1012,
901. HRMS (ESI) m/z calc’d (positive mode) for C50H66O4N [M+H]+
744.4992, found 744.5026.
3,9-bis(2,6-bis(hexyloxy)phenyl)-4,4a1-dihydroindolizino[6,5,4,3-
ija]quinolone (5b): To a flame dried, N2 filled flask was added 1-(2,6-
bis((2,6-bis(hexyloxy)phenyl)ethynyl)phenyl)-1H-pyrrole (4b), (6.90 mg,
9.27 mmol, 1.0 equiv.), InCl3 (1.23 g, 5.58 mmol, 0.60 equiv.) and toluene
(46.5 ml, 0.2 M). The mixture was stirred at 100oC overnight. The reaction
was filtered through
a pad of silica gel, eluting with 50 %
dichloromethane/hexanes to give the desired product as a yellow oil (1.08
1
g, 95%). H NMR (500 MHz, CDCl3) d = 7.80 (d, J = 8.6 Hz, 2H), 7.75 (d,
J = 8.6 Hz, 2H), 7.69 (s, 1H), 7.65 (d, J = 8.1 Hz, 1H), 7.44 (d, J = 8.1 Hz,
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10.1002/chem.201800030
Chemistry - A European Journal
FULL PAPER
1H), 7.21 (s, 1H), 7.10 (d, J = 7.3 Hz, 2H), 7.08 (d, J = 7.3 Hz, 2H). 4.21-
3.95 (m, 4H), 3.53 (s, 1H), 2.00-1.75 (m, 4H), 1.74-1.20 (m, 12H), 0.96 (t,
J = 6.8 Hz, 6H). 13C NMR (125 MHz, CDCl3) d = 159.5, 159.5, 133.9, 133.6,
131.4, 130.8, 130.6, 129.6, 129.6, 129.4, 128.2, 128.1, 127.5, 127.1, 127.0,
126.3, 118.5, 118.2, 117.3, 114.7, 114.7, 109.8, 107.2, 82.8, 81.7, 68.2,
31.7, 29.8, 29.4, 28.3, 25.9, 22.7, 14.2 IR (neat, cm−1): 3312, 2925, 2855,
2334, 2093, 1602, 1503, 1493, 1389, 1299, 1276, 1240, 1171, 1110, 1032,
824, 792. HRMS (ESI) m/z calc’d (positive mode) for C40H41O2NCs [M
+Cs]+ 700.2192, found 700.2186.
1.2
equiv.),
and
6-bromo-4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-
b']dithiophene-2-carbaldehyde (10)[11] (40.0 mg, 0.088 mmol, 1.0 equiv.).
The mixture was stirred at room temperature overnight. The reaction
mixture was then diluted with dichloromethane and extracted with
dichloromethane/H2O, dried by Na2SO4 and evaporated. The product was
then purified through silica gel chromatography with 50% diethyl
ether:hexanes to give the desired product as a red solid (79 mg, 97%). 1H
NMR (300 MHz, CDCl3) d = 9.88 (s, 1H), 7.82 (d, J = 8.5 Hz, 2H), 7.76 (d,
J = 8.6 Hz, 2H), 7.70 (s, 1H), 7.66 (d, J = 8.1 Hz, 1H), 7.59 (s, 1H), 7.46
(d, J = 8.0 Hz, 1H), 7.29 (d, J = 5.7 Hz, 1H), 7.22 (br. s, 3H), 7.11 (dd, J =
8.8 Hz, 8.7 Hz, 4H), 4.26-4.00 (m, 4H), 2.30-0.60 (m, 48H). 13C NMR (125
MHz, CDCl3) d = 182.6, 161.8, 159.6, 159.5, 158.9, 147.2, 143.8, 136.7,
134.1, 133.8, 131.6, 130.7, 130.5, 129.8, 129.6, 129.5, 128.0, 127.5, 127.3,
127.2, 126.8, 126.4, 125.7, 118.8, 118.4, 117.4, 114.8, 114.8, 110.1, 107.4,
107.4, 95.5, 88.3, 68.2, 37.7, 31.6, 31.6, 29.7, 29.7, 29.3, 25.8, 24.6, 22.7,
22.6, 14.1, 14.0. IR (neat, cm−1): 3303, 3051, 2926, 2856, 2179, 1657,
1604, 1503, 1393, 1369, 1246, 1176, 834. HRMS (ESI) m/z calc’d (positive
mode) for C62H69O3NS2 [M]+ 939.4719, found 939.4890.
3,9-bis(2,6-bis(hexyloxy)phenyl)-5-ethynylindolizino[6,5,4,3-
ija]quinoline (8b): The synthesis follows the same procedure as 5-
ethynyl-3,9-bis(4-(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinoline
(8a)
except 3,9-bis(2,6-bis(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinoline-5-
carbaldehyde (6b, 64.3 mg) was used in place of 3,9-bis(4-
(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinoline-5-carbaldehyde (6a). The
reaction mixture was extracted by DCM and H2O, dried with Na2SO4 and
evaporated. The crude mixture was purified through silica gel
chromatography using 50% dichloromethane:hexane as the eluent to give
a pure yellow oil (54.3 mg, 85%). 1H NMR (500 MHz, CDCl3) d = 7.67 (s,
1H), 7.63 (d, J = 8.0 Hz, 1H), 7.43-7.31 (m, 3H), 7.23 (s, 1H), 6.68-6.60
(m, 6H), 4.20-3.80 (m, 8H), 3.43 (s, 1H), 1.70-1.42 (m, 8H), 1.29-1.00 (m,
24H), 0.73 (ap t, 12H). 13C NMR (75 MHz, CDCl3) d = 158.2, 158.2, 132.1,
129.3, 129.2, 127.8, 127.5, 127.4, 127.3, 127.2, 126.5, 120.9, 119.9, 117.5,
116.9, 116.7, 109.0, 106.5, 106.4, 105.5, 105.5, 105.5, 83.3, 80.6, 68.9,
68.9, 31.3, 31.3, 28.9, 28.9, 25.5, 25.5, 22.4, 22.4, 13.8, 13.8. IR (neat,
cm−1): 3307, 2927, 2862, 1591, 1457, 1421, 1395, 1366, 1297, 1247, 1098,
1027, 872. HRMS (ESI) m/z calc’d (positive mode) for C51H65O5NCs
[M+Cs]+ 900.3968, found 900.3716.
6-((3,9-bis(2,6-bis(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinolin-5-
yl)ethynyl)-4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-b']dithiophene-2-
carbaldehyde (11b): The synthesis follows the same procedure as 6-
((3,9-bis(4-(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinolin-5-yl)ethynyl)-
4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-b']dithiophene-2-carbaldehyde (11a)
except
3,9-bis(2,6-bis(hexyloxy)phenyl)-5-ethynylindolizino[6,5,4,3-
ija]quinoline (8b, 55.8 mg) was used in place of 5-ethynyl-3,9-bis(4-
(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinoline (8a). The crude mixture
was purified through silica gel chromatography using 50%
dichloromethane:hexanes as the eluent to give a red solid (17.4 mg, 21%).
1H NMR (500 MHz, CDCl3) d = 9.84 (s,1H), 7.65 (s,1H), 7.61 (d, J =8.1 Hz,
1H), 7.56 (s,1H), 7.45-7.29 (m, 3H), 7.21 (s,1H), 7.14 (s,1H), 6.81-6.64 (m,
6H), 4.05-3.90 (m, 8H), 2.00-1.80 (m, 4H), 1.70-0.79 (m, 54H), 0.79-0.61
(m, 12H). 13C NMR (125 MHz, CDCl3) d = 182.5, 161.8, 158.7, 158.2, 158.1,
147.5, 143.5, 136.1, 132.2, 129.8, 129.4, 128.7, 127.6, 127.4, 127.4, 127.1,
126.6, 125.4, 121.2, 120.0, 117.8, 117.0, 116.6, 116.5, 109.2, 106.9, 106.7,
105.4, 105.4, 105.4, 96.4, 87.4, 69.0, 68.9, 54.1, 37.8, 31.6, 31.3, 31.3,
29.4, 28.9, 28.9, 25.6, 25.5, 24.6, , 22.6, 22.4, 22.3, 14.0, 13.0, 13.8. IR
(neat, cm−1): 3367, 3063, 2923, 2851, 1656, 1592, 1496, 1458, 1421, 1395,
1364, 1302, 1247, 1098. HRMS (ESI) m/z calc’d (positive mode) for
C74H93O5NS2Cs [M+Cs]+ 1272.5550, found 1272.5785.
4-ethynyl-3,9-bis(4-(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinoline
(9a): The synthesis follows the same procedure as 5-ethynyl-3,9-bis(4-
(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinoline (8a) except 3,9-bis(4-
(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinoline-4-carbaldehyde (7a, 280
mg)[3c] was used in place of 3,9-bis(4-(hexyloxy)phenyl)indolizino[6,5,4,3-
ija]quinoline-5-carbaldehyde (6a). The crude mixture was purified through
silica gel chromatography using 50% dichloromethane:hexanes as the
eluent to give the pure product (253 mg, 91%). 1H NMR (300 MHz,
Acetone-d6) d = 7.87 (d, J = 6.7 Hz, 1H), 7.70 (d, J = 8.5 Hz, 2H) , 7.67 (d,
J = 8.4 Hz, 2H), 7.60 (d, J = 7.7 Hz, 1H), 7.52 (t, J = 7.7 Hz, 1H), 7.34 (s,
1H), 7.13-6.97 (m, 5H), 6.84 (d, J = 4.3 Hz, 1H), 4.13-4.00 (m, 4H), 3.99
(s, 1H), 1.90-1.71(m, 4H), 1.60-1.25 (m, 12H), 1.11-0.80 (m, 6H). 13C NMR
(75 MHz, acetone-d6) d = 159.6, 137.3, 132.6, 131.2, 130.9, 130.2, 129.2,
128.6, 127.5, 126.9, 125.7, 125.0, 124.1, 120.2, 119.3, 118.6, 114.7, 114.0,
109.1, 108.6, 107.0, 86.4, 80.2, 67.8, 67.8, 31.5, 25.6, 25.6, 22.4, 13.5. IR
(neat, cm−1): 3279, 2924, 2856, 1976, 1604, 1507, 1428, 1406, 1395, 1360,
1278, 1244, 1174, 1116, 1071, 1027, 830. HRMS (ESI) m/z calc’d (positive
mode) for C40H41O2NCs [M + Cs]+ 700.2192, found 700.2178.
6-((3,9-bis(4-(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinolin-4-
yl)ethynyl)-4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-b']dithiophene-2-
carbaldehyde (12a): The synthesis follows the same procedure as 6-
((3,9-bis(4-(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinolin-5-yl)ethynyl)-
4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-b']dithiophene-2-carbaldehyde (11a)
only 4-ethynyl-3,9-bis(4-(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinoline
(9a, 41.3 mg) was used in place of 5-ethynyl-3,9-bis(4-
(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinoline (8a). The crude mixture
was purified through silica gel chromatography using 10% acetone:
hexane as the eluent to give a red solid (39 mg, 57%). 1H NMR (500 MHz,
CDCl3) d = 9.88 (s, 1H), 7.96 (br t, 1H), 7.81 (d, J = 8.5 Hz, 2H), 7.74 (d, J
= 8.4 Hz, 2H), 7.62-7.52 (m, 3H), 7.32 (s, 1H), 7.18-6.97 (m, 6H), 7.00 (d,
J = 4.1 Hz, 1H), 4.13 (t, J = 6.4 Hz, 2H), 4.07 (t, J = 6.5 Hz, 2H), 2.00-1.80
(m, 8H), 1.69-1.49 (m, 8H), 1.49-0.89 (m, 21H), 0.86 (t, J = 6.8 Hz, 12H).
13C NMR (125 MHz, CDCl3) d = 182.6, 161.8, 159.5, 159.4, 158.9, 147.1,
143.7, 136.9, 136.4, 132.8, 131.6, 131.2, 130.5, 129.8, 129.3, 128.9, 128.1,
127.9, 127.3, 125.8, 125.5, 124.6, 124.1, 120.0, 119.7, 118.7,114.8, 114.2,
109.4, 109.0, 107.3, 94.5, 91.6, 68.2, 68.2, 37.7, 32.0, 31.7, 31.6, 31.6,
31.6, 29.7, 29.6, 29.4, 29.3, 29.2, 25.8, 25.8, 24.6, 22.7, 22.7, 22.7, 22.6,
22.6, 14.1, 14.1, 14.0, 14.0. IR (neat, cm−1): 3020, 2925, 2855, 2362, 2335,
1651, 1504, 1463, 1395, 1362, 1260, 1175, 1023, 892. HRMS (ESI) m/z
calc’d (positive mode) for C62H69O3NS2Cs [M + Cs]+ 1072.3773, found
1072.3646.
3,9-bis(2,6-bis(hexyloxy)phenyl)-4-ethynylindolizino[6,5,4,3-
ija]quinoline (9b): The synthesis follows the same procedure as 5-
ethynyl-3,9-bis(4-(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinoline
(8a)
except 3,9-bis(2,6-bis(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinoline-4-
carbaldehyde (7b, 466 mg) was used in place of 3,9-bis(4-
(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinoline-5-carbaldehyde (6a). The
reaction mixture was extracted by dichloromethane and H2O, dried with
Na2SO4 and evaporated. The crude mixture was purified through silica gel
chromatography using 50% dichloromethane:hexanes as the eluent to
give a yellow oil (153 mg, 33%). 1H NMR (300 MHz, CDCl3) d = 7.44 (br s,
3H), 7.38-7.25 (m, 2H), 7.18 (d, J = 8.5 Hz, 2H), 6.70 (d, J = 8.3 Hz, 2H),
6.64 (ap d, 3H), 4.08-3.80 (m, 8H), 2.59 (s, 1H), 1.68-1.40 (m, 8H), 1.38-
0.99 (m, 24H), 0.81-0.59 (m, 12H). 13C NMR (125 MHz, CDCl3) d = 158.8,
158.1, 132.4, 129.3, 129.2, 128.4, 126.6, 126.1, 126.0, 126.0, 125.9, 123.6,
123.0, 122.3, 119.3, 119.1, 116.3, 116.2, 109.7, 105.4, 105.0, 99.2, 79.2,
77.6, 68.9, 68.9, 31.3, 31.3, 29.0, 28.9, 25.6, 25.5, 22.4, 22.4, 13.8, 13.8.
IR (neat, cm−1): 3310, 2926, 2861, 1589, 1457, 1388, 1296, 1247, 1097,
871. HRMS (ESI) m/z calc’d for (positive mode) C52H66O4N [M+H]+
768.4992, found 768.4495.
6-((3,9-bis(2,6-bis(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinolin-4-
yl)ethynyl)-4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-b']dithiophene-2-
carbaldehyde (12b): To a flame dried, N2 filled round bottom flask was
added
6-bromo-4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-b']dithiophene-2-
carbaldehyde (10)[11] (34 mg, 0.075 mmol, 1.0 equiv.), Pd(PPh3)4 (13.9 mg,
6-((3,9-bis(4-(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinolin-5-
yl)ethynyl)-4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-b']dithiophene-2-
carbaldehyde (11a): To a flame dried N2 filled round bottom flask was
added CuI (0.67 mg, 0.003 mmol, 0.04 equiv.), dioxane (0.18 ml),
diisopropylamine ( 0.03 ml, 0.211 mmol, 2.4 equiv.), Pd[P(t-Bu)3]2 (2.69 mg,
0.012 mmol, 0.16 equiv.) and dry N,N-dimethylformamide (10.8 ml, 0.007
M).
A
separate solution of 3,9-bis(2,6-bis(hexyloxy)phenyl)-4-
((tributylstannyl)ethynyl)indolizino[6,5,4,3-ija]quinoline (13b) (158 mg,
0.15 mmol, 2.0 equiv.) in dry N,N-dimethylformamide (2.5 ml, 0.06 M) was
added dropwise followed with stirring at 110oC and the mixture was stirred
overnight. The reaction was cooled down to room temperature and
0.005
mmol,
0.06
equiv.),
5-ethynyl-3,9-bis(4-
(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinoline (8a) (60 mg, 0.106 mmol,
This article is protected by copyright. All rights reserved.

10.1002/chem.201800030
Chemistry - A European Journal
FULL PAPER
mg, 30%). 1H NMR (400 MHz, d6-DMSO, 85oC) d = 8.00 (s, 1H), 7.91 (d,
J = 7.2 Hz, 1H), 7.80-7.72 (m, 4H), 7.66 (t, J = 7.6 Hz, 1H), 7.61 (s, 1H),
7.48 (s, 1H), 7.31 (s, 1H), 7.19 (d, J = 8.4 Hz, 2H), 7.16-7.11 (m, 3H), 6.95
(d, J = 4.4 Hz, 1H), 6.09 (s, 1H), 4.15 (t, J = 6.8 Hz, 2H), 4.11-4.09 (t, J =
6.8 Hz, 2H), 1.94-1.76 (m, 8H), 1.54-1.48 (m, 4H), 1.48-1.13 (m, 20H),
0.95-0.77 (m, 16H) 13C NMR spectrum could not be obtained due to the
sparing solubility of this dye. IR (neat, cm−1): 3400, 2955, 2921, 2852, 2335,
1729, 1580, 1569, 1509, 1461, 1360, 1290, 1254, 1170, 1087, 1019, 797.
HRMS (ESI) m/z calc’d (negative mode) for C65H69O4N2S2 [M-H]-
1005.4699, found 1005.4708. UV-Vis (CH2Cl 2): λmax = 543 nm (ε = 28,000
M−1 cm−1), λonset = 690 nm. CV (0.1 M Bu 4 NPF 6 in CH2Cl2, sweep width
2.0-(-1.2.0), 0.1 Vs-1 scan rate) versus NHE: E (S+/S) = 0.90 V; Egopt = 1.84
eV. E (S+/S*) = –0.94 V [vs NHE, calculated from E (S+/S*) = (E (S+/S) – E gopt )].
extracted with diethylether and H2O. The crude product was further purified
by silica column chromatography with 10% ethyl acetate:hexanes to give
a red solid (39 mg, 46%). 1H NMR (300 MHz, CDCl3) d = 9.85 (s, 1H), 7.57
(s, 1H), 7.51-7.41 (m, 3H), 7.36 (dd, J = 9.1 Hz, J = 8.5 Hz, 2H), 7.23 (s,
1H), 7.19 (s, 1H), 6.72 (d, J = 8.2 Hz, 2H), 6.71 (d, J = 8.4 Hz, 2H), 6.67
(d, J = 4.7 Hz, 1H), 6.67 (d, J = 4.7 Hz, 1H), 4.10-3.79 (m, 8H), 2.00-1.75
(m, 4H), 1.75-1.42 (m, 8H), 1.42-0.80 (m, 46H), 0.80-0.60 (m, 12H). 13C
NMR (125 MHz, CDCl3) d = 182.4, 161.6, 158.5, 158.5, 158.3, 158.2, 158.2,
147.9, 143.0, 135.0, 132.4, 129.8, 129.6, 129.4, 127.9, 126.8, 126.6, 126.0,
125.4, 123.8, 123.6, 122.5, 119.6, 119.4, 116.2, 116.0, 109.0, 105.5, 105.5,
105.2, 105.2, 99.6, 93.6, 85.0, 68.9, 68.9, 37.7, 31.7, 31.3, 31.3, 29.7,
29.7, 29.0, 25.6, 25.5, 24.6, 22.6, 22.5, 22.4, 14.0, 13.9, 13.9. IR (neat,
cm−1): 3311, 3052, 2926, 2857, 1655, 1590, 1495, 1458, 1421, 1396, 1300,
1228, 1120, 1098, 870.6. HRMS (ESI) m/z calc’d (positive mode) for
C74H93O5NS2 [M]+ 1139.6495, found 1139.6481.
(E)-3-(6-((3,9-bis(2,6-bis(hexyloxy)phenyl)indolizino[6,5,4,3-
ija]quinolin-5-yl)ethynyl)-4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-
b']dithiophen-2-yl)-2-cyanoacrylic acid (YZ14): The synthesis follows
3,9-bis(2,6-bis(hexyloxy)phenyl)-4-
((tributylstannyl)ethynyl)indolizino[6,5,4,3-ija]quinoline (13b): To a N2
filled flame dried round bottom flask was added 3,9-bis(2,6-
bis(hexyloxy)phenyl)-4-ethynylindolizino[6,5,4,3-ija]quinoline (9b) (100 mg,
0.13 mmol, 1.0 equiv.) and dry THF (4.4 ml, 0.03M). The solution was
cooled to -78oC, then 2.5 M n-BuLi in hexane (0.06 ml, 0.15 mmol, 1.16
equiv.) was added at -78oC and stirred for 2.5 hours. Bu3SnCl (0.04 ml,
0.14 mmol, 1.1 equiv.) was added and the whole reaction was stirred at
room temperature for 2.5 hours. The reaction mixture was extracted with
diethyl ether and H2O, dried with Na2SO4 and evaporated to get the crude
product that was used without further purification in the next step (137 mg,
100%). 1H NMR (300 MHz, CDCl3) d = 7.45-7.24 (m, 5H), 7.10 (d, J = 2.7
Hz, 2H), 6.68 (d, J =8.4, 2H), 6.65-6.55 (m, 3H), 4.01-3.80 (m, 8H), 1.81-
0.80 (m, 59H), 0.80-0.60 (m, 12H).
the
same
procedure
as
(E)-3-(6-((3,9-bis(4-
(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinolin-5-yl)ethynyl)-4,4-dihexyl-
4H-cyclopenta[2,1-b:3,4-b']dithiophen-2-yl)-2-cyanoacrylic acid (YZ7)
except 6-((3,9-bis(2,6-bis(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinolin-
5-yl)ethynyl)-4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-b']dithiophene-2-
carbaldehyde (11b, 17.0 mg) was used in place of 6-((3,9-bis(4-
(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinolin-5-yl)ethynyl)-4,4-dihexyl-
4H-cyclopenta[2,1-b:3,4-b']dithiophene-2-carbaldehyde (11a). Also, after
the silica gel plug filtration, the crude product was further purified by
reverse phase column (C18 silica) with 80% MeOH:acetonitrile to give a
red solid (11 mg, 61%). H NMR (300 MHz, d6-DMSO, 40oC) d = 8.02 (s,
1
1H), 7.69-7.62 (m, 2H), 7.53 (d, J = 7.8 Hz, 1H), 7.49-7.35 (m, 3H), 7.25
(s, 1H), 7.11-7.08 (m, 1H), 6.83 (ap t, J = 7.8 Hz, 4H), 6.61-6.50 (m, 2H),
4.00-3.90 (m, 8H), 1.90-1.85 (m, 4H), 1.50-0.50 (m, 66H). 13C NMR
spectrum could not be obtained due to the sparing solubility of this dye. IR
(neat, cm−1): 3050, 2922, 2854, 1732, 1605, 1458, 1361, 1254, 1099, 843.
HRMS (ESI) m/z calc’d (negative mode) for C77H93O6N2S2 [M-H]+
1205.6475, found 1205.6469. UV-Vis (CH2Cl2): λmax = 537 nm (ε = 28,000
M−1 cm−1), λonset = 700 nm. CV (0.1 M Bu4 NPF6 in CH2Cl2, sweep width
2.0-(-1.2.0), 0.1 Vs-1 scan rate) versus NHE: E (S+/S) = 0.71 V; Egopt = 1.79
eV; E (S+/S*) = -1.08 V [vs NHE, calculated from E(S+/S*) = (E(S+/S) – Egopt )].
(E)-3-(6-((3,9-bis(4-(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinolin-5-
yl)ethynyl)-4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-b']dithiophen-2-yl)-2-
cyanoacrylic acid (YZ7): To a round bottom flask was added 6-((3,9-
bis(4-(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinolin-5-yl)ethynyl)-4,4-
dihexyl-4H-cyclopenta[2,1-b:3,4-b']dithiophene-2-carbaldehyde (11a) (40
mg, 0.04 mmol, 1.0 equiv.) and CHCl3 (0.17 ml). The mixture was
degassed with N2 for 30 minutes, then cyanoacetic acid (11 mg, 0.13 mmol,
3.0 equiv.) and piperidine (0.03 mL, 0.29 mmol, 7.0 equiv.) were added
into the flask. The flask was sealed with a plastic stopper and electrical
tape and stirred at 90oC for 10 hours. To the reaction mixture was added
acetic acid, then the mixture was directly purified through a silica gel plug
using first 100% dichloromethane, followed by 10% methanol:90%
dichloromethane, and finally 10% methanol:2% acetic acid:88%
dichloromethane. Then the dye was again extracted with hexane and
water to remove acetic acid and trace silica gel particles. The organic layer
was concentrated under reduced pressure to give a purple solid. The
product was suspended in hexane solvent then centrifuged five times to
give the pure product (43 mg, 97%). 1H NMR (400 MHz, CDCl3/d6-DMSO,
85oC) d = 8.14 (s, 1H), 7.82 (d, J = 8.4 Hz, 2H), 7.77 (d, J = 8.4 Hz, 2H),
7.69 (s, 1H), 7.65 (d, J = 8.4 Hz, 1H), 7.60-7.55 (m, 2H), 7.44 (d, J = 6.4
Hz, 2H), 7.22 (s, 2H), 7.18-7.10 (m, 4H), 4.11 (ap dt, J = 6.4, 2.0 Hz, 4H),
1.95-1.90 (m, 4H), 1.81 (ap pent, J = 7.2 Hz, 4H), 1.55-1.46 (m, 4H), 1.40-
1.36 (m, 8H), 1.18-1.13 (m, 12H), 0.95-0.90 (m, 10H), 0.81 (t, J = 6.8 Hz,
6H). 13C NMR spectrum could not be obtained due to the sparing solubility
of this dye. IR (neat, cm−1): 3413, 2923, 2854, 2361, 2335, 1600, 1560,
1505, 1366, 1295, 1249, 1174, 1086, 1028, 799. HRMS (ESI) m/z calc’d
(negative mode) for C65H69O4N2S2 [M-H]- 1005.4699, found 1005.3744.
UV-Vis (CH2Cl2): λmax = 532 nm (ε = 29,000 M−1 cm−1), λonset = 650 nm. CV
(0.1 M Bu4NPF6 in CH2Cl2, sweep width 2.0-(-1.2.0), 0.1 Vs-1 scan rate)
versus NHE: E(S+/S) = 0.90 V; Egopt = 1.88 eV. E (S+/S*) = –0.98 V [vs NHE,
calculated from E(S+/S*) = (E(S+/S) – Egopt)].
(E)-3-(6-((3,9-bis(2,6-bis(hexyloxy)phenyl)indolizino[6,5,4,3-
ija]quinolin-4-yl)ethynyl)-4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-
b']dithiophen-2-yl)-2-cyanoacrylic acid (YZ15): The synthesis follows
the
same
procedure
as
(E)-3-(6-((3,9-bis(4-
(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinolin-5-yl)ethynyl)-4,4-dihexyl-
4H-cyclopenta[2,1-b:3,4-b']dithiophen-2-yl)-2-cyanoacrylic acid (YZ7)
except 6-((3,9-bis(2,6-bis(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinolin-
4-yl)ethynyl)-4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-b']dithiophene-2-
carbaldehyde (12b, 18.9 mg) was used in place of 6-((3,9-bis(4-
(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinolin-5-yl)ethynyl)-4,4-dihexyl-
4H-cyclopenta[2,1-b:3,4-b']dithiophene-2-carbaldehyde (11a). Also, after
the silica gel plug filtration, the crude product was further purified by silica
gel chromatography with 5% MeOH:35% dichloromethane:60% hexanes
to give a red solid (6.2 mg, 31%). 1H NMR (300 MHz, d6-DMSO, 40 oC) d
= 7.64-7.35 (m, 5H), 7.18 (s, 2H), 6.85-6.74 (m, 5H), 6.66 (s, 1H), 6.52 (s,
1H), 6.43 (s, 1H), 3.94 (br s, 8H), 1.90-1.75 (m, 4H), 1.50-0.50 (m, 66H).
13C NMR spectrum could not be obtained due to the sparing solubility of
this dye. IR (neat, cm−1): 3025, 2926, 2856, 1588, 1458, 1373, 1290, 1251,
1098, 1019, 869. HRMS (ESI) m/z calc’d (negative mode) for
C77H93O6N2S2 [M - H]+ 1205.6475, found 1205.7507. UV-Vis (CH2Cl 2):
λmax = 549 nm (ε = 26,000 M−1 cm−1), λonset = 690 nm. CV (0.1 M Bu4 NPF6
in CH2Cl2, sweep width 2.0-(-1.2.0), 0.1 Vs-1 scan rate) versus NHE: E
(S+/S) = 0.84 V; Egopt = 1.89 eV; E(S+/S*) = –1.05 V [vs NHE, calculated from
E (S+/S*) = (E(S+/S) – Egopt )].
(E)-3-(6-((3,9-bis(4-(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinolin-4-
yl)ethynyl)-4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-b']dithiophen-2-yl)-2-
cyanoacrylic acid (YZ12): The synthesis follows the same procedure as
(E)-3-(6-((3,9-bis(4-(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinolin-5-
yl)ethynyl)-4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-b']dithiophen-2-yl)-2-
Acknowledgements
cyanoacrylic
acid
(YZ7)
except
6-((3,9-bis(4-
YZ, HC and JHD thank the National Science Foundation for
generous support through a CAREER award 1455167. LM, AHL
and NIH thank NSF for award OIA-1539035
(hexyloxy)phenyl)indolizino[6,5,4,3-ija]quinolin-4-yl)ethynyl)-4,4-dihexyl-
4H-cyclopenta[2,1-b:3,4-b']dithiophene-2-carbaldehyde (12a, 20.2 mg)
was used in place of 6-((3,9-bis(4-(hexyloxy)phenyl)indolizino[6,5,4,3-
ija]quinolin-5-yl)ethynyl)-4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-
b']dithiophene-2-carbaldehyde (11a). Also, after the silica gel plug filtration,
the crude product was further purified by silica gel column chromatography
with 60% DCM:10% methanol:30% hexane to give a pure purple solid (6.5
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10.1002/chem.201800030
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Keywords: dye-sensitized solar cells • ullazine • panchromatic •
dyes • molecular engineering
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10.1002/chem.201800030
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Entry for the Table of Contents (Please choose one layout)
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Yanbing Zhang, † Hammad Cheema, †
Louis McNamara, Leigh Anna Hunt,
Nathan I. Hammer, Jared H. Delcamp*
A series of metal-free ullazine based
D-π-A dyes have been designed and
synthesized for the first time. These
dyes were characterized by UV-Vis-
NIR absorption spectroscopy, cyclic
Page No. – Page No.
voltammetry,
analysis, which
characteristics for use in DSC devices.
A PCE of 5.6% was obtained for the
highest performing dye in the series
with a good IPCE onset of 800 nm.
and
computational
reveal suitable
Ullazine Donor-
p
bridge-Acceptor
Organic Dyes for DSCs
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