Naphthyl derivatives functionalised with electron acceptor units - Synthesis, electronic characterisation and DFT calculations

Article abstract of DOI:10.1002/ejoc.201200715

A series of unsymmetrical dyes containing a naphthyl unit connected to an electron acceptor moiety was designed and synthesised. By modifying the electron acceptor unit, a shift of the LUMO energy level as well as its distribution through the molecule were achieved. These dyes were fully characterised by optical, computational and electrochemical techniques. In addition, crystal structures reveal different packing depending upon the nature of the acceptor. Their potential use as electron acceptor materials for organic photovoltaics (OPVs) was also investigated by photoluminescence studies of blends with the common OPV polymers P3HT and PCDTBT. A series of unsymmetrical dyes was synthesised and characterised. Their optical and electrochemical properties were tuned by modifying the electron acceptor unit. Copyright

Full text of DOI:10.1002/ejoc.201200715

Job/Unit: O20715
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Date: 30-07-12 18:30:29
Pages: 8
FULL PAPER
DOI: 10.1002/ejoc.201200715
Naphthyl Derivatives Functionalised with Electron Acceptor Units – Synthesis,
Electronic Characterisation and DFT Calculations
[a]
[a]
Miquel Planells and Neil Robertson*
Keywords: Donor–acceptor systems / Organic photovoltaics / Density functional calculations / Electrochemistry / Lumines-
cence
A series of unsymmetrical dyes containing a naphthyl unit
connected to an electron acceptor moiety was designed and
synthesised. By modifying the electron acceptor unit, a shift
of the LUMO energy level as well as its distribution through
the molecule were achieved. These dyes were fully charac-
terised by optical, computational and electrochemical tech-
niques. In addition, crystal structures reveal different pack-
ing depending upon the nature of the acceptor. Their poten-
tial use as electron acceptor materials for organic photovol-
taics (OPVs) was also investigated by photoluminescence
studies of blends with the common OPV polymers P3HT and
PCDTBT.
Introduction
stituent moieties. This offers a modular synthetic approach
from common building blocks; however, the suitability of
differing acceptor units, in terms of both electronic and
structural properties, requires further study. Accordingly, in
this paper we will address the synthesis, optical and electro-
chemical characterisation and DFT calculations of a series
of dyes containing the naphthyl π system as a core unit
and the modification of the acceptor by attaching different
electron withdrawing groups. This provides a series of fun-
damental model compounds to explore the effect of the dif-
ferent acceptor units. The attachment of cyano and fluori-
nated groups on the acceptor moiety allows fine-tuning of
the molecular electronic properties. We also evaluate the so-
lid-state packing properties of compounds 1, 3 and 4 as well
as photoluminescence quenching with common electron do-
nor polymers.
Organic semiconductor materials have attracted the at-
tention of both the academic and the industrial community
due to their potential use in low-cost and lightweight or-
ganic electronic devices, such as organic photovoltaics
(OPVs). The most widely used active layer for these OPVs,
the so-called Bulk-heterojunction OPV, is based on a blend
of P3HT (electron donor) and PCBM (electron ac-
[
1–6]
ceptor).
This has been widely developed and studied
during the last decade. Although extensive research has
been done to obtain better electron donor materials with
improved efficiencies, less success has been achieved in the
[
7]
development of alternative electron acceptor materials.
This is due to the unique properties of fullerene and its
derivatives such as good charge transport and the formation
of a favourable morphology when blended with an acceptor
[
8,9]
polymer.
Because of their high cost and limited light
harvesting, however, replacing the fullerene derivative in
OPVs is an important target and a significant current chal-
lenge. In this context, an interesting approach consists of
developing new molecules containing electron withdrawing
groups. By this approach, several materials have been syn-
Results and Discussion
Electron acceptor units were synthesised as shown in
Scheme 1. Indane derivatives 7 and 9 were prepared by con-
densation of malononitrile (2 or 3 equiv. for 7 and 9, respec-
tively) to commercially available 1,3-indanedione.[
Tetrafluoroindane derivative 6 was obtained by reacting
tetrafluorophthalic anhydride with tert-butyl acetoacet-
[10–11]
[12]
thesised, such as modified pentacene,
perylene,
[
13]
[14]
phthalocyanines,[15] thio-
benzothiazoles,
vinazene,
[
16]
[17]
phene-S,S-oxide and bifluorenylidene compounds.
A straightforward and attractive approach to new ac-
ceptor molecules comprises the combination of a simple,
common core aromatic unit with electron withdrawing sub-
18–19]
[
20]
ate, and tricyanofurane 8 (TCF) was prepared by a two-
step condensation of malononitrile in basic media.[
Chromophores 1–5 were prepared by a condensation of 2-
naphthaldehyde with acceptors 6–9 following different syn-
thetic procedures, depending on the nature of the acceptor,
and collected by filtration.
21,22]
[
a] EastChem School of Chemistry, University of Edinburgh,
West Mains Road, Edinburgh EH9 3JJ, U.K.
Fax: +44-131 650 6453
E-mail: neil.robertson@ed.ac.uk
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201200715.
Eur. J. Org. Chem. 0000, 0–0
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M. Planells, N. Robertson
FULL PAPER
accordingly the shift of the ICT band is related to the elec-
tron acceptor strength. Therefore, molecule 1 (with a
weaker electron withdrawing unit) showed a maximum at
360 nm, whereas a redshift was observed when fluorine
atoms (molecule 2) or cyano groups (molecules 3 and 4)
were introduced. This redshift reached up to 80 nm as we
increased the electron acceptor ability. Additionally, these
dyes also show a solvatochromic effect, which is expected
for such donor–acceptor molecules and indicates a signifi-
cant difference in charge distribution between the ground
and excited states (Figures S1 and S2 – Supporting Infor-
[
24]
mation). In this case, an increase in solvent polarity leads
to a blueshifted absorption maximum, indicating a re-
duction in the dipole moment of the excited state relative
to that of the ground state of the dye.
Scheme 1. Synthesis of acceptors 1–5.
The stability of these new compounds was tested by
keeping the dyes for a few days in CDCl or [D ]DMSO
3
6
1
solutions and monitoring them by H NMR spectroscopy.
All the chromophores showed good stability, except for mol-
ecule 5. In this case, a peak at δ = 10 ppm appeared after
one day, which indicated that 5 had decomposed into start-
ing materials 2-naphthaldehyde and acceptor 9. This result
is not unexpected, because chromophore 5 exhibits signifi-
cant strain between the naphthyl and tetracyanoindane unit
and therefore a high tendency to dissociate (Figure 1). We
believe that traces of water in the solvent drive the system
back to starting materials, and therefore molecule 5 can
only be obtained and treated in an anhydrous environment,
such as acetic anhydride.[
23]
Figure 2. Absorption of 1 (black line), 2 (red line), 3 (blue line)
and 4 (green line) recorded in CH
2
Cl
2
at room temperature. Inset:
Emission spectrum of 4 in CH Cl at room temperature after exci-
2 2
tation at 430 nm.
Table 1. Electrochemical and optical data for 1–4.
opt
CV
E
gap
/eV
λ
/
max
nm[a]
ε
λ
em
λ
/nm
onset
E
/eV
gap
E
/V
OX
E
/V
RED
/cm m–1 /nm
–1
[b]
[c]
[c]
[d]
e]
1
2
3
4
360
370
440
430
35000
34000
16000
38000
450[
n.o.
440
460
2.82
2.69
2.48
2.45
+1.36
+1.38
+1.47
+1.38
–1.41
–1.20
–1.04
–1.11
2.77
2.58
2.51
2.49
[f]
n.o.[ 500
f]
545
505
2 2
Cl m
. [b] Measured at 5ϫ10–6
[
a] Measured at 5ϫ10–5 m in CH
in CH Cl and excited at λmax. [c] Differential pulse voltammetry
DPV) measured from 0.1 m [TBA][PF ] in CH Cl and referenced
2
2
(
6
2
2
1
to ferrocene. [d] Cyclic voltammetry: Egap (CV) = EOX – ERED. [e]
Low intensity. [f] The abbreviation n.o. means not observed.
Figure 1. H NMR spectra of pristine 5 (top) and after 24 h (bot-
tom) in [D
6 degrees.
6
]DMSO. DFT calculations show a large ring twist of
5
Electrochemical behaviour was investigated by cyclic vol-
Optical properties were measured by UV/Vis absorption tammetry (CV) and differential pulse voltammetry (DPV)
and photoluminescence techniques in dichloromethane in a CH Cl solution containing 0.1 m [TBA][PF ] as sup-
2
2
6
solution. All dyes showed a strong absorption peak centred porting electrolyte. All values are reported in Table 1. As
between 360 and 500 nm, and most of them showed fluores- expected, oxidation potentials remain similar for all sam-
cence emission. Spectroscopic data are shown in Figure 2 ples, consistent with a HOMO based on the naphthyl unit
and summarised in Table 1 together with the electrochemi- in each case. These potentials are at the edge of the solvent
cal properties. The intense absorption in the visible region window and can only be observed by the DPV technique
is assigned to an intramolecular charge transfer (ICT) from (Figures S3 and S4 – Supporting Information). On the
the naphthyl π-system to the electron acceptor unit, and other hand, reduction potentials shifted to more positive
2
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Naphthyl Derivatives Functionalised with Electron Acceptor Units
potentials as the electron withdrawing ability of the mole-
cule increased, that is, when the number of cyano/fluori-
nated units increased. All the first reduction processes could
be observed by both CV and DPV, and they showed an
irreversible wave (Figure 3). Although electrochemically
irreversible waves indicate that radical anions are not stable
on the electrochemical timescale, the molecule is reduced
only transiently in the solid state solar cell and can still
possess sufficient stability for model studies.
Figure 4. Molecular orbital distribution (isodensity = 0.03) and or-
bital energies calculated for molecules 1–4 (from left to right) at
the B3LYP/6-31G(d,p) level of theory.
As shown in Figure 5, the packing follows a head-to-tail
motif for all samples, characteristic of non-symmetrical do-
nor–acceptor molecules, in order to cancel the dipole mo-
[
25–26]
ment.
Acceptors 1, 2 and 3 pack as a dimer, with alter-
nating (overlapping) naphthyl units over indanedione moie-
ties. In contrast, acceptor 4 packs by overlapping two naph-
thyl units, without involving the TCF moiety. This could be
due to the steric hindrance of the methyl groups of the TCF
unit, which are out of plane.
Figure 3. Cyclic voltammetry of 4 performed at different scan rates
2 2 6
(CH Cl , 0.1 m [TBA][PF ], V vs. Ag/AgCl).
DFT calculations were performed at the Gaussian 03,
B3LYP 6-31G(d,p) level of theory. Computational details
can be found in the Supporting Information. Figure 4
shows representations of the highest occupied (HOMO)
and lowest unoccupied (LUMO) molecular orbitals. It can
be observed that the HOMO is localised over the naphthyl
unit and the ethylene bridge. The orbital energies calculated
are similar (ca. –6.0 eV) for all the molecules. In contrast,
localisation of the LUMO varies depending on the nature
of the acceptor. In general, the LUMO is delocalised on
Figure 5. Packing of 1, 2, 3 and 4. Additional asymmetric units (if
any) are shown in different colours.
Intradimer distances were 3.29 (3.30), 3.24, 3.31 (3.41)
either the indane or TCF unit, together with the ethylene and 3.42 (3.61) Å for 1, 2, 3 and 4, respectively, showing a
bridge. Fluorinated analogue 2 shows a lower LUMO en- strong π–π interaction between units within the same range
[
27]
ergy relative to non-fluorinated analogue 1 (0.2 eV), al- for all samples. However, the twist between the naphthyl
though the LUMO is slightly distributed on the fluorine unit and the acceptor moiety is different. In this case, we
atoms. On the other hand, the addition of cyano groups observe a small twist of 2, 2 and 8 degrees for molecules 1,
(molecules 3 and 4) leads to a strong downward shift of the 2 and 4, respectively. On the other hand, molecule 3, with
LUMO energy by 0.5 eV, relative to that of 1. In this case, similar packing to 1 and 2, shows a twist angle as high as
the molecular orbital distribution is localised on the cyano 18 degrees. This nonplanar packing for a fully conjugated
groups together with the ethylene moieties.
molecule 3 is consistent with its poorer crystallinity.
Although the absolute values do not agree with the ex-
Photoluminescence quenching of blends is a useful and
perimental values obtained by CV and DPV, the trend and straightforward technique to screen the potential use of or-
shift in energy between molecules is consistent. ganic semiconductors in OPV applications. In this case, we
Single crystals suitable for X-ray diffraction were ob- formed 1:1 blends of acceptors 1, 3 and 4 with both poly-
tained by slow recrystallisation in hot 1-butanol for 1 and mers P3HT and PCDTBT through spin coating of solutions
chlorobenzene for 2 and 4. Multiple attempts were per- containing 5 mgmL–1 of each component in chlorobenzene
formed to obtain crystals from solution processing for mol- solvent. We discarded samples 2 and 5 because of their low
ecule 3, with no success. However, suitable crystals were ob- solubility and low stability, respectively. Spin coating stud-
tained after sublimation.
ies typically use concentrations around 10 mgmL–1 or
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M. Planells, N. Robertson
FULL PAPER
higher; however, the solubility limit of 1 and 4 is around the fact that the LUMO energy levels suggest a good energy
–
1
5
mgmL , and therefore blends were sonicated and vigor- offset for exciton splitting. We believe that P3HT, consid-
ously stirred at 40 °C in order to dissolve them completely. ered as a strongly crystalline polymer, did not blend well
The mixture was spin coated onto slightly warm glass to with the more crystalline acceptors 1 and 4, but better with
avoid microprecipitation. In order to study the thin film 3, the acceptor we found most difficult to crystallise from
stability as well as the light absorption contribution of the solution. On the other hand, when it is blended with
synthesised electron acceptor materials in the solid state, PCDTBT, which is considered to be a more amorphous
UV/Vis absorption spectra were recorded and monitored polymer, molecule 3 shows a nearly complete photolumi-
over four days for the acceptors blended with PCDTBT nescence quenching, but only a 90% quenching is observed
[
28]
polymer (Figures S7 and S8 – Supporting Information). for molecule 4. This suggests that molecule 3 intercalates
Bands due to the acceptor absorption can be observed at better into the polymer than 4, probably because of the
similar positions to solution experiments, and no significant lower tendency for molecules of 3 to pack with each
[
28–29]
changes were observed during the next four days. After other.
Although better photoluminescence quenching
proving the stability of the films, photoluminescence has been found for 3 because of its less crystalline nature,
quenching was followed after excitation at 520 and 550 nm we note that its charge transport properties could also be
for P3HT and PCDTBT, respectively (Figure 6).
affected. Finally, photoluminescence quenching of 1 with
PCDTBT blend is not observed as a result of the very small
energy offset, considering the low-lying LUMO of
PCDTBT. This is consistent with the results observed by
electrochemistry and DFT calculations.
Conclusions
We designed and synthesised four electron acceptor ma-
terials based on a naphthyl group with different electron
withdrawing units. All these molecules were characterised
by spectroscopic, electrochemical and computational tech-
niques. These molecules possess an intense band between
350 and 500 nm, and most of them have a reduction poten-
tial suitable for mixing with typical electron donor poly-
mers. In spite of this, photoluminescence quenching clearly
indicates other factors that should be taken in account,
such as the crystallinity of the materials used. In this case,
only molecule 3 gave good quenching with both P3HT and
PCDTBT, while 4 showed good quenching with just
PCDTBT. We have interpreted this in terms of the crystal
structure of 3, which shows a larger twist in the molecule,
possibly enhancing its tendency to blend with the polymer.
In general, we have demonstrated that π systems attached
to electron withdrawing groups can provide the right elec-
trochemical and optical properties for a new approach to
electron acceptor materials for OPV. Further studies are in
progress to explore their properties in OPV devices and to
prepare analogues that build on the morphological insight
gained.
Experimental Section
Materials and Reagents: All reagents were purchased from either
Sigma–Aldrich or Alfa–Aesar, and they were used as received with-
out further purification, except for 1,3-indanedione and 2-naphth-
aldehyde that were recrystallised from ethanol before use.
Figure 6. Photoluminescence quenching of P3HT (top) and
PCDTBT (bottom) after blending with acceptor 1, 3 and 4 at a
ratio of 1:1 in chlorobenzene. Photoluminescence intensities have
been corrected for the absorption of the film and then normalised
to the maximum emission of the polymer.
2
-(Naphthalen-2-ylmethylene)-1H-indene-1,3(2H)-dione
Naphthaldehyde (100 mg, 0.64 mmol) and 1,3-indanedione
103 mg, 1.1 mmol) were placed in a Schlenk tube with n-butyl
(1):
2-
Figure 4 shows good P3HT photoluminescence quench-
(
–
1
ing for molecule 3; however, the photoluminescence alcohol (25 mL, 40 mLmmol ). The mixture was stirred under N
2
quenching for molecules 1 and 4 is inefficient, in spite of for 5 h. After cooling to room temp., a yellow precipitate was col-
4
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Naphthyl Derivatives Functionalised with Electron Acceptor Units
lected by filtration and washed with ethanol (50 mL). Yield 54 mg
2
der N for 3 h. After cooling to room temp., a red precipitate was
1
(30%). Melting point: 223 °C. H NMR (500 MHz, CDCl
3
): δ
H
=
collected by filtration and washed with ethanol (50 mL). Yield
1
8
(
(
1
1
.95 (s, 1 H), 8.62 (dd, J = 8.6, 1.9 Hz, 1 H), 8.07 (m, 4 H), 7.94
d, J = 8.6 Hz, 1 H), 7.89 (d, J = 7.7 Hz, 1 H), 7.84 (m, 2 H), 7.62
m, 1 H), 7.56 (m, 1 H) ppm. 13C NMR (125 MHz, CDCl
): δ
90.6, 189.4, 147.3, 142.8, 140.3, 136.9, 135.7, 135.6, 135.4, 133.2,
31.1, 130.0,129.5, 129.3, 129.2, 128.6, 127.9, 126.9, 123.5 (ϫ2)
50 mg (32 %). Melting point = 196 °C. H NMR (500 MHz,
3 H
CDCl ): δ = 8.80 (s, 1 H), 8.75 (d, J = 8.0 Hz, 1 H), 8.69 (s, 1 H),
8.26 (dd, J = 8.7, 1.9 Hz, 1 H), 7.99 (t, J = 9.0 Hz, 2 H), 7.92 (d,
J = 8.6 Hz, 1 H), 7.89 (d, J = 8.3 Hz, 1 H), 7.85 (td, J = 7.5, 1.9 Hz,
3
C
=
1 H), 7.80 (td, J = 7.4, 0.9 Hz, 1 H), 7.63 (m, 1 H), 7.57 (m, 1 H)
+
13
ppm. MS EI (m/z): [M] calcd. for C20
H
12
O
2
: 284.0837, found
3 C
ppm. C NMR (125 MHz, CDCl ): δ = 186.6, 161.9, 148.2,
2
8
84.08318. C20
4.38, H 4.14.
H
12
O
2
(284.31): calcd. C 84.49, H 4.25; found C
140.0, 137.6, 136.8, 135.9, 135.7, 135.3, 132.9, 130.4, 130.0, 129.9,
129.5, 129.5, 129.1, 128.2, 128.0, 127.1, 125.6, 124.6, 114.3, 114.0,
–
7
3
2.7 ppm. MS ESI (m/z): [M – H] calcd. for C23
H
11
N
2
O:
Tetrafluoro-1,3-indanedione (6): Tetrafluorophthalic anhydride (2 g,
.1 mmol) was added into a round-bottomed flask with acetic an-
12 2
31.08659, found 331.08777. C23H N O (332.36): calcd. C 83.12,
9
H 3.64, N 8.43; found C 83.20, H 3.57, N 8.39.
–1
hydride (9 mL, 1 mLmmol ) and triethylamine (4.5 mL,
–1
0
.5 mLmmol ). The mixture was stirred at room temp., and tert-
butyl acetoacetate (1.66 mL, 10 mmol) was added. The reaction
mixture was kept at room temp. and stirred overnight under N
-[3-Cyano-4,5,5-trimethylfuran-2(5H)-ylidene]malononitrile (8):[30]
2
3-Hydroxy-3-methylbutanone (3.5 mL, 33.3 mmol) and malonon-
2
.
itrile (4.4 g, 66.6 mmol) were added into a two-neck round-bot-
Then, the crude mixture was poured into a 1:1 mixture (10 g) of
ice-water and conc. HCl. An additional amount (16 mL) of HCl
–1
tomed flask with ethanol (83 mL, 2.5 mLmmol ). Then, a freshly
made sodium ethoxide solution (100 mg sodium in 1 mL ethanol)
(
5 m) was added, and the mixture was stirred at reflux for 3 h. After
cooling at room temp., the crude was extracted by adding CHCl
150 mL). The organic layer was washed with brine, dried with
Na SO , and the solvent was removed to give a brown solid. The
pure product was obtained by sublimation under high vacuum at
was added, and the mixture was stirred overnight under N
0 °C. After cooling down at room temp., the solvent was removed
and the product was purified by column chromatography (CH Cl ).
An analytical sample was obtained by recrystallisation in ethanol
2
at
3
8
(
2
2
2
4
1
as yellowish needles (3.2 g, 48%). H NMR (500 MHz, CDCl
=
3
): δ
H
1
1
40 °C as a white solid (540 mg, 27%). H NMR (400 MHz,
13
2.36 (s, 3 H), 1.63 (s, 6 H) ppm. C NMR (125 MHz, CDCl
3
):
CDCl
=
for C
3
): δ
H
= 3.33 (s, 2 H) ppm. 19F NMR (376 MHz, CDCl
3
): δ
F
C
δ = 182.2, 175.2, 111.1, 110.4, 109.1, 105.1, 99.7, 59.0, 24.6, 14.3
+
–135.2 (m, 2 F), –140.1 (m, 2 F) ppm. MS EI (m/z): [M] calcd.
+
ppm. MS ESI (m/z): [M + H] calcd. for C11
found 200.08207. C11 O (199.21): calcd. C 66.32, H 4.55, N
1.09; found C 66.41, H 4.68, N 20.85.
10 3
H N O: 200.08184,
9 2 2 4 9 2 4 2
H O F : 217.99854, found 217.99835. C H F O (218.11):
9 3
H N
calcd. C 49.56, H 0.92; found C 49.57, H 1.00.
2
4
,5,6,7-Tetrafluoro-2-(naphthalen-2-ylmethylene)-1H-indene-1,3-
(
2
1
E)-2-{3-Cyano-5,5-dimethyl-4-[2-(naphthalen-2-yl)vinyl]furan-
(
(
2H)-dione (2): 2-Naphthaldehyde (155 mg, 1.0 mmol) and 6
327 mg, 1.5 mmol) were placed in a Schlenk tube with n-butyl
[30]
(5H)-ylidene}malononitrile (4):
2-Naphthaldehyde (155 mg,
.0 mmol) and 8 (219 mg, 1.1 mmol) were placed in a Schlenk tube
–1
alcohol (20 mL, 20 mLmmol ). The mixture was stirred under N
2
–1
with ethanol (4 mL, 4 mL mmol ). Triethylamine (13 μL,
.1 mmol) was added, and the mixture was stirred under N over-
overnight at reflux. After cooling to room temp. a yellow precipi-
tate was collected by filtration and washed with ethanol (50 mL).
Yield 77 mg (20%). Melting point: 300 °C. 1H NMR (400 MHz,
0
2
night at reflux temperature. After cooling to room temp., a red
precipitate was collected by filtration and washed with cold ethanol
[
8
(
–
3
D
6
]DMSO): δ
.07 (m, 4 H), 7.73 (m, 1 H), 7.66 (m, 1 H) ppm. F NMR
376 MHz, [D ]DMSO): δ = 139.8 (m, 1 F), –141.1 (m, 1 F),
143.9 (m, 2 F) ppm. MS EI (m/z): [M] calcd. for C20
56.04604, found 356.045513. C20 (356.27): calcd. C 67.42,
H
= 9.04 (s, 1 H), 8.64 (dd, J = 8.88, 1.3 Hz, 1 H),
1
(
(
20 mL). Yield 253 mg (75 %). Melting point: 275 °C. H NMR
1
9
500 MHz, CDCl
3
): δ
H
= 8.07 (s, 1 H), 7.92 (m, 2 H), 7.88 (d, J =
6
F
8
.0 Hz, 1 H), 7.84 (d, J = 16.2 Hz, 1 H), 7.76 (dd, J = 8.8, 1.8 Hz,
H), 7.59 (m, 2 H), 7.15 (d, J = 16.3 Hz, 1 H), 1.84 (s, 6 H) ppm.
C NMR (125 MHz, CDCl ): δ = 175.4, 173.8, 147.6, 135.5,
3 C
33.4, 132.9, 131.5, 129.8, 129.3, 129.2, 128.3, 127.7, 122.9, 115.1,
+
8 4 2
H F O :
1
H
8
F
4
O
2
13
H 2.26; found C 67.51, H 2.17.
1
1
11.8, 111.0, 110.4, 100.1, 97.8, 58.2, 26.7 ppm. MS ESI (m/z): [M –
2
1
-(3-Oxo-indane-1-ylidene)-malononitrile (7): 1,3-indanedione (2 g,
–
H] calcd. for C22
C H N O (337.38): calcd. C 78.32, H 4.48, N 12.46; found C
22 15 3
7
14 3
H N O: 336.11314, found 336.11438.
3.68 mmol) and malononitrile (1.8 g, 66.06 mmol) were placed in
–
1
a round-bottomed flask with ethanol (30 mL, 2 mLmmol ). The
mixture was stirred at room temp., and sodium acetate (1.34 g,
8.28, H 4.36, N 12.37.
1
6.4 mmol) was added. The reaction mixture was kept at room
(
1
Indan-1,3-diylidene)dimalononitrile (9): 1,3-Indanedione (2 g,
temp. and stirred for 40 min. Then, H O (130 mL) was added and
2
3.68 mmol) and malononitrile (2.7 g, 41.04 mmol) were placed in
the crude mixture was acidified by adding concentrated HCl drop-
wise until pH = 2. The mixture was stirred for an extra 10 min,
and the grey precipitate was filtered off and washed with copious
amounts of water. The solid was recrystallised twice with acetic
–
1
a round-bottomed flask with ethanol (30 mL, 2 mLmmol ). The
mixture was stirred at room temp., and ammonium acetate (1.05 g,
1
7
3.68 mmol) was added. The reaction mixture was heated up to
0 °C and stirred for 5 h. After cooling down to room temp., H
2
O
1
acid and with ethanol to obtain a reddish solid (1.07 g, 41%). H
(
40 mL) was added and the crude mixture was acidified by adding
NMR (500 MHz, CDCl
J = 7.0 Hz, 1 H), 7.88 (m, 2 H), 3.73 (s, 2 H) ppm. C NMR
125 MHz, CDCl ): δ = 194.9, 166.4, 142.6, 140.7, 136.3, 135.9,
26.2, 124.9, 112.3, 122.2, 79.4, 43.4 ppm. MS EI (m/z): [M] calcd.
for C12 ON : 194.04856, found 194.04851. C12 O (194.19):
calcd. C 74.22, H 3.11, N 14.43; found C 74.02, H 3.05, N 14.36.
3 H
): δ = 8.66 (d, J = 7.5 Hz, 1 H), 7.99 (d,
concentrated HCl dropwise until pH = 2. The crude mixture was
stirred for an extra 10 min, and the grey precipitate was filtered off
and washed with copious amounts of water. The solid was recrys-
13
(
1
3
C
+
1
tallised with acetic acid to give brown crystals (1.15 g, 34%). H
H
6
2
6 2
H N
NMR (500 MHz, CDCl
3
): δ
s, 2 H) ppm. C NMR (125 MHz, CDCl
136.4, 127.1, 111.9, 111.7, 79.4, 42.0 ppm. MS ESI (m/z): [M – H]
H
= 8.66 (m, 2 H), 7.92 (m, 2 H), 4.30
1
3
(
3
): δ = 165.4, 140.7,
C
(Z)-2-[2-(Naphthalen-2-ylmethylene)-3-oxo-2,3-dihydro-1H-inden-1-
–
ylidene]malononitrile (3): 2-Naphthaldehyde (72 mg, 0.47 mmol)
and 7 (100 mg, 0.51 mmol) were placed in a Schlenk tube with n-
butyl alcohol (20 mL, 40 mLmmol ). The mixture was stirred un-
5 4 6 4
calcd. for C15H N : 241.05197, found 241.05191. C15H N
(242.24): calcd. C 74.37, H 2.50, N 23.13; found C 74.26, H 2.40,
N 23.23.
–1
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
5

Job/Unit: O20715
/KAP1
Date: 30-07-12 18:30:29
Pages: 8
M. Planells, N. Robertson
FULL PAPER
2
,2Ј-[2-(Naphthalen-2-ylmethylene)-1H-indene-1,3(2H)-diylidene]di-
malononitrile (5): 2-Naphthaldehyde (155 mg, 1.0 mmol) and 9
266 mg, 1.1 mmol) were placed in a Schlenk tube with acetic anhy-
Nichol (University of Edinburgh) for the crystal structure data col-
lection, refinement and discussion. We thank Prof. James Durrant
(Imperial College London) for providing us with P3HT and
PCDTBT polymers.
(
–1
dride (8 mL, 8 mLmmol ). The mixture was stirred under N
2
for
4
h. at reflux temperature. After cooling to room temp., a red-
brown precipitate was collected by filtration and washed with cold
acetic anhydride (4 mL). Yield 39 mg (10%). H NMR (500 MHz,
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[
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1
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19
[
[
19
Bruker Advance 400 spectrometer (376 MHz for F). The deuter-
1
ated solvents are indicated; chemical shifts, δ, are given in ppm,
1
13
referenced to the solvent residual signal ( H, C). Mass spectra
were recorded with a ThermoElectron MAT 900 (electron impact,
EI) or a LCQ Thermo Finnegan (electrospray ionisation, ESI) in-
strument, depending on the sample. Elemental analyses were car-
ried out by Stephen Boyer at London Metropolitan University with
a Carlo Erba CE1108 Elemental Analyser.
4
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Cl
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by using
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[
[
2
electrode was a Pt disk. The reference electrode was Ag/AgCl, and
the counter electrode was a Pt rod. All measurements were made
at room temp. with an μAUTOLAB Type III potentiostat, driven
by the electrochemical software GPES. Cyclic voltammetry (CV)
[
–1
measurements used scan rates of 0.1 Vs , and DPV was carried
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minescence spectra were recorded with a Fluoromax-2 fluorimeter
controlled by the ISAMain software. All samples were measured
in a 1 cm cell at room temp. with dichloromethane as a solvent.
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Cl
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[
32]
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19
13
[
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Acknowledgments
We thank the Engineering and Physical Sciences Research Council
(EPSRC) APEX project for financial support. We thank Dr. Gary
6
www.eurjoc.org
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 0000, 0–0

Job/Unit: O20715
/KAP1
Date: 30-07-12 18:30:29
Pages: 8
Naphthyl Derivatives Functionalised with Electron Acceptor Units
[
[
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Published Online: ᭿
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
7

Job/Unit: O20715
/KAP1
Date: 30-07-12 18:30:29
Pages: 8
M. Planells, N. Robertson
FULL PAPER
Organic Photovoltaics
A series of unsymmetrical dyes was syn-
thesised and characterised. Their optical
and electrochemical properties were tuned
by modifying the electron acceptor unit.
M. Planells, N. Robertson* ............... 1–8
Naphthyl Derivatives Functionalised with
Electron Acceptor Units – Synthesis, Elec-
tronic Characterisation and DFT Calcu-
lations
Keywords: Donor–acceptor systems / Or-
ganic photovoltaics / Density functional
calculations / Electrochemistry / Lumi-
nescence
8
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