Dicyanobenzene and dicyanopyrazine derived X-shaped charge-transfer chromophores: Comparative and structure-property relationship study

Article abstract of DOI:10.1039/c4ob00901k

A series of novel X-shaped push-pull compounds based on benzene-1,2-dicarbonitrile has been designed, synthesized and further investigated by X-ray analysis, electrochemistry, absorption and emission spectra, SHG experiment and quantum-chemical calculations. The obtained data were compared with those for isolobal 5,6-disubstituted pyrazine-2,3- dicarbonitriles. Structure-property relationships were elucidated. The extension, composition and planarization of the π-linker used as well as the electron-withdrawing ability of both dicyano-substituted acceptor units affect the linear and nonlinear properties of the target charge-transfer chromophores most significantly. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c4ob00901k

Organic &
Biomolecular Chemistry
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Dicyanobenzene and dicyanopyrazine derived
X-shaped charge-transfer chromophores:
comparative and structure–property relationship
study†
Cite this: Org. Biomol. Chem., 2014,
12, 5517
L. Dokládalová,‡a F. Bureš,*a W. Kuznik,b,c I. V. Kityk,c A. Wojciechowski,c T. Mikysek,d
N. Almonasy,a M. Ramaiyan,a Z. Padělková,e J. Kulháneka and M. Ludwiga
A series of novel X-shaped push–pull compounds based on benzene-1,2-dicarbonitrile has been
designed, synthesized and further investigated by X-ray analysis, electrochemistry, absorption and emis-
sion spectra, SHG experiment and quantum-chemical calculations. The obtained data were compared
with those for isolobal 5,6-disubstituted pyrazine-2,3-dicarbonitriles. Structure–property relationships
were elucidated. The extension, composition and planarization of the π-linker used as well as the elec-
tron-withdrawing ability of both dicyano-substituted acceptor units affect the linear and nonlinear pro-
perties of the target charge-transfer chromophores most significantly.
Received 2nd May 2014,
Accepted 3rd June 2014
DOI: 10.1039/c4ob00901k
www.rsc.org/obc
(OLEDs), dye-sensitizing solar cells (DSSCs), semiconductors,
Introduction
switches, etc.1–3 Spatial arrangement of a push–pull system
Organic molecules based on the sp2/sp hybridized carbon/ involves prevailing linear (D–π-A), quadrupolar (D–π-A–π-D or
hetero atom scaffold end-capped with electron donors and A–π-D–π-A) and octupolar/tripodal ((D-π)3-A or (A-π)3-D)
acceptors represent an intensively investigated area of organic systems or less common V- (ref. 4), Y- (ref. 5), H- (ref. 6) and
chemistry. In these molecules, intramolecular charge-transfer X-shaped molecules. X-shaped chromophores based on tetra-
(ICT) from the donor (D) to the acceptor (A) via a π-conjugated substituted ethenes (tetraethynylethenes, TEEs, and cyanoethy-
system takes place and the D–π-A systems become polarized nylethenes, CEEs) were introduced and extensively studied
and gain dipolar character. Due to the ICT, push–pull D–π-A mainly by Diederich and co-workers.7,8 Besides the ethene
molecules possess distinct linear as well as nonlinear optical central π-linker, the 1,2,4,5-tetrasubstituted benzene pattern
(NLO) properties. Charge-transfer chromophores have found represents another class of X-shaped chromophores. Benzene-
widespread applications in modern branches of materials derived X-shaped chromophores can conveniently be prepared
chemistry such as optoelectronics, data processing and storage from catechol, o-phenylenediamine or tetrahalogenated
devices, NLO bioimaging, organic light-emitting diodes benzenes via functionalization with suitable electron donors
(e.g. NR2 and OR groups) and acceptors (e.g. NO2 group and
π-deficient heterocycles). Such molecules were mainly investi-
aInstitute of Organic Chemistry and Technology, University of Pardubice, Faculty of
gated for their unique absorption/emission properties and
Chemical Technology, Studentská 573, Pardubice, 53210, Czech Republic.
chelating abilities towards metal ions.9
E-mail: filip.bures@upce.cz
Recently, we have designed and synthesized X-shaped chro-
mophores based on the pyrazine skeleton.10 Herein we would
extend the concept of X-shaped chromophores with two elec-
tron withdrawing cyano groups saturated with two electron
donors attached opposite to a six-membered (hetero)aromate.
Thus, the previous series of pyrazines P1–P10 was completed
with analogous push–pull chromophores B1–B10 featuring the
benzene central π-system.
Both chromophore types possess a N,N-dimethylamino
donor connected via systematically extended π-linkers that
comprise a combination of up to three acetylene and 1,4-
phenylene subunits. In contrast to polyenes and polyynes,
bDepartment of Experimental Physics, University of Debrecen, Bem sq. 18/a, 4026
Debrecen, Hungary
cElectrical Engineering Department, Czestochowa University of Technology, Armii
Krajowej 17, Czestochowa, 42201, Poland
dDepartment of Analytical Chemistry, University of Pardubice, Faculty of Chemical
Technology, Studentská 573, Pardubice, 53210, Czech Republic
eDepartment of General and Inorganic Chemistry, University of Pardubice, Faculty of
Chemical Technology, Studentská 573, Pardubice, 53210, Czech Republic
†Electronic supplementary information (ESI) available: General information,
synthesis and characterization of 11, further crystallographic, electrochemical,
spectroscopic data, SHG results and HOMO/LUMO localizations in B1–B10, 1H
and 13C NMR spectra of B1–B10. CCDC 984735 and 984736. For ESI and crystal-
lographic data in CIF or other electronic format see DOI: 10.1039/c4ob00901k
‡Present address: COC Ltd, Rybitví 296, 53354, Pardubice, Czech Republic.
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(oligo)phenylene ethynylene charge-transfer chromophores mercially available phthalimide. In contrast to Terekhov et al.,
possess generally higher thermal and (photo)chemical stabi- iodination of phthalimide with I2/oleum (30%) and one recrys-
lity. 4,5-Disubstituted benzene-1,2-dicarbonitrile derivatives tallization from acetone afforded directly 4,5-diiodophthali-
are a currently intensively investigated class of compounds due mide in 61% yield without the need for Soxlet extraction and
to their easy transformation to (sub)phthalocyanines. Peripher- column chromatography.17 However, it should be noted that
ally substituted phthalocyanines found widespread appli- regioselective outcome and yield of the iodination step depend
cations in NLO,11 DSSCs,12 supramolecular assemblies,13 strongly on the concentration of the oleum used. Subsequent
discotic liquid crystals14 and photodynamic therapy.15 ammonolysis to 4,5-diiodophthaldiamide and dehydration
Recently, Adachi et al. showed highly efficient OLEDs from with (CF3CO)2O/pyridine afforded compound 11 in 42% overall
delayed fluorescence that utilize similar push–pull dicyano- yield (see the ESI† for more details).17 Similarly to pyrazines
benzene derivatives functionalized with carbazole moieties.16
P1–P10, benzene derivatives B1–B10 were obtained by Suzuki–
Miyaura and Sonogashira cross-coupling reactions. N,N-Di-
methylamino-substituted π-linkers with boronic acid (ester)
function and terminal acetylene moiety were prepared from
commercially available or known short π-linkers18 and their
extension/alternation by cross-coupling reactions with [(4-iodo-
phenyl)ethynyl]trimethylsilane.10,19
With
the
extended
π-linkers and 4,5-diiodobenzene-1,2-dicarbonitrile 11 in hand,
we have carried out twofold Suzuki–Miyaura cross-coupling
reactions leading to target molecules B1, B3 and B4 in yields
of 83, 87 and 79% (Scheme 1). These chromophores possess
the π-linker connected directly to the dicyanobenzene moiety
via a 1,4-phenylene unit. This twisted arrangement usually rep-
resents a barrier of efficient D–A interaction.10 Therefore,
partial planarization of the π-linker has been achieved via
introduction of an additional acetylene unit by Sonogashira
reaction. The reaction of 11 with terminal acetylenes afforded
target chromophores B2 and B5–B10 with the yields ranging
from 62 to 92% (Scheme 2). All target compounds B1–B10
were isolated in similar yields as pyrazines P1–P10 and were
purified by column chromatography and recrystallization from
1,2-dichloroethane/hexane. In contrast to compounds B7 and
B8, pyrazine analogues P7 and P8 could not be prepared. In
these cases, the final Sonogashira reactions were dominated
by homocoupling of the starting acetylenes and pyrazine
derivatives P7 and P8 were only detected in the crude reaction
We report here the design and synthesis of charge-transfer
chromophore series B1–B10 with a systematically evaluated
π-conjugated path and the elucidation of the structure–prop-
erty relationships. The extent of the ICT and linear and non-
linear optical properties were studied by X-ray analysis,
electrochemistry, absorption/emission spectra, semi-empirical
computational methods and second harmonic generation
(SHG) experiments.
Results and discussion
Synthesis
The synthesis of target chromophores B1–B10 has been mixture as minor products. Due to the dipolar character and
extended π-system of B1–B10, some target compounds are only
carried out in a modular manner starting from 4,5-diiodoben-
zene-1,2-dicarbonitrile 11, which can be prepared from com- sparingly soluble in halogenated solvents. However, their
Scheme 1 Suzuki–Miyaura reaction leading to chromophores B1, B3 and B4.
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Scheme 2 Twofold Sonogashira reaction leading to chromophores B2 and B5–B10.
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chemical structures have been confirmed by NMR, HR-MALDI- phore molecular plane. Pyrazine P1 adopts a similar angular
MS and IR spectra as well as elemental analysis and X-ray arrangement which is most likely caused by the steric repul-
analysis.
sion of the ortho-hydrogens. Whereas in benzene derivatives
B1/B4 are both 1,4-phenylene moieties twisted perpendicularly
to the adjacent benzene-1,2-dicarbonitrile moiety and adopt
mutually almost parallel arrangement with minimal ϕ1 = 7/10°
and high torsion angles ϕ5/ϕ6 = 42–51°, the derivative P1 pos-
sesses these substituents twisted mainly above/below the pyra-
zine plane with relatively high both torsion angles ϕ1 = 25°
and ϕ5/ϕ6 = 30/29°. This arrangement results in substantial
deformation of the pyrazine ring compared to almost planar
benzene rings (see ϕ2–4 in Table 1). The differences in spatial
arrangements of the C4/C5 and C5/C6 substituents in benzene
B1/B4 and pyrazine P1 derivatives are visualized in the side
views (Fig. 1). The overlap wire model for isolobal compounds
B1/P1 is also provided in Fig. 1d.
Crystallography
Slow diffusion of hexane into solution of chromophores B1
and B4 in CH2Cl2/CDCl3 afforded crystals suitable for X-ray
analysis. Fig. 1(a/b) shows the ORTEP plots and side views of
both molecules and confirms the proposed molecular struc-
ture. The ORTEP plot of previously crystallized pyrazine P1 has
also been included as a reference (Fig. 1c).10 The spatial
arrangement of the central dicyano acceptor moieties and the
adjacent 1,4-phenylene units in B1, B4 and P1 can be evalu-
ated by the dihedral angles ϕ1–ϕ6 as shown in Fig. 1 and
Table 1.
As can be seen, both donor-substituted π-linkers attached
on the benzene-1,2-dicarbonitrile acceptor moiety via a 1,4-
phenylene unit are significantly twisted out of the chromo-
Bond length alternation (BLA) in the N,N-dimethylanilino
(DMA) and 1,4-phenylene rings can easily be evaluated by the
quinoid character (δr). Whereas in benzene, δr is equal to 0, in
a
fully quinoid ring, δr would be on the order of
0.100–0.120 Å.20 A comparison with known CT chromophores
bearing DMA moieties such as CEEs (δr up to 0.070 Å)8 and
TEEs (δr up to 0.025 Å)7 places the nonplanar benzene and pyr-
azine chromophores B1/B4 and P1 below/at the level of donor-
substituted tetraethynylethenes. Further comparison of the δr
values for B1/P1 shown in Table 1 clearly indicates higher BLA
in the pyrazine chromophore P1. Estimation of the aromaticity
of both central benzene and pyrazine rings by the calculation
of the Bird index (I6)21 provides similar insight. Whereas the I6
values of unsubstituted benzene/pyrazine are 100/88.8, the cal-
culated values for B1, B4 and P1 decrease in the same order of
89.9→88.9→82.2 as a consequence of the π-system extension
and replacement of the central benzene by the pyrazine ring.
1H NMR and IR spectroscopy
We analysed the 13C NMR spectra of all B and P chromophores
measured in CDCl3 (100 MHz) as well as IR spectra measured
neat using an HATR adapter. Electron saturation of the CN
group indicated by 13C NMR chemical shift and frequency of
vibrational stretching would serve as good indicators of the
ICT extent (Table 2).
The chemical shift of C atoms strongly depends on hybrid-
ization and the electron density at the nucleus. The higher the
electron density, the more shielding occurs and an upfield
shift will be observed.8c The data in Table 2 clearly demon-
strate that 13C NMR shifts of the CN group in pyrazine series
of compounds (P1–P4) are generally upfielded as a conse-
quence of higher saturation of the CN group compared to com-
pounds B1–B4. Introduction of more electronegative acetylene
units as in chromophores B6–B10 reduces the electron satur-
ation of the CN group, which is then engaged similarly in the
ICT, and the chemical shifts became steady at around
114 ppm. However, when comparing the particular com-
pounds B1/B2 or P1/P2 that differ in the type of connection of
the π-linker to the acceptor moiety (without/with an additional
acetylene unit), the chemical shifts of the latter were upfielded
Fig. 1 ORTEP representations and spatial arrangements of chromo-
phores B1 (a), B4 (b) and P1 (c) measured at 150 K and the overlap wire
model for isolobal chromophores B1/P1 (d). The thermal ellipsoids are
shown at 50% probability with arbitrary spheres for H atoms.
Table 1 RTG-derived structural parameters of chromophores B1, B4
and P1
a
a
a
a
a
c
Compd
ϕ1
ϕ2
ϕ3
ϕ4
ϕ5/ϕ6
δrb
I6
B1
B4
P1
7
10
25
2
5
18
2
4
13
3
4
7
51/45
48/42
30/29
0.011
0.010/0.013
0.027
89.9
88.9
82.2
a The torsion angles ϕ1–6 are in deg. b The average quinoid characters
δr of 1,4-phenylene and DMA units are given in Å. c The Bird index of
the central benzene/pyrazine rings.
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Table 2 13C NMR chemical shifts and frequency of the stretching
vibration of the CuN group
Table 3 Electrochemical data for chromophores 1–10
oF
oF
(red1)
Compd
E
a [V]
E
a [V]
ΔEb [V]
(ox1)
Compd
δ(CuN)a
ν(CuN)b
B1/P1
B2/P2
B3/P3
B4/P4
B5/P5
B6/P6
B7/—
B8/—
B9/P9
B10/P10
+0.92/+1.02
+0.93/+1.04
+0.80/+0.81
+0.84/+0.83
+0.81/+0.84
+0.89/+0.85
+0.78/—
+0.78/—
+0.84/+0.84
+0.84/+0.83
−1.62/−1.24
−1.28/−0.87
−1.48/−1.05
−1.41/−0.97
−1.14/−0.74
−1.07/−0.69
−1.32/—
2.54/2.26
2.21/1.91
2.28/1.86
2.25/1.80
1.95/1.58
1.96/1.54
2.10/—
1.87/—
1.94/1.54
1.87/1.50
B1/P1
B2/P2
B3/P3
B4/P4
B5/P5
B6/P6
B7/—
B8/—
B9/P9
B10/P10
116.27/114.33
112.59/112.17
114.19/113.68
114.62/113.43
113.83/c
2223/2230
2177/2165
2224/2340
2202/2194
2200/2182
2206/2189
2203/—
2202/—
2202/2188
2202/2190
114.29/c
c/—
−1.09/—
−1.10/−0.70
−1.03/−0.67
114.41/—
114.21/c
114.47/c
a EoF = (Ep,c + Ep,a)/2 where Ep,c and Ep,a correspond to the cathodic and
anodic peak potentials, respectively. bΔE = E
a 13C NMR chemical shift of the CN group given in ppm – measured in
CDCl3 at 100 MHz. b Frequency of the vibrational stretching of the CN
group given in cm−1 – measured by IR (neat, HATR). c Not observed
due to sparing solubility in CDCl3.
oF
(ox1)
oF
(red1)
− E
.
oF
reduction potentials only negligibly. However, the E
values
(ox1)
slightly decrease with the extension of the π-system as a result
of the gradual N,N-dimethylamino donor isolation. From chro-
mophores B3/P3 onwards, the first oxidation potentials were
concentrated in the range of about +0.80 V, and therefore, the
N,N-dimethylamino donor in chromophores 4–10 can be con-
sidered as similarly involved in the ICT.
by 3.68 and 2.16 ppm. This observation can be attributed to
planarization of the entire π-system and thus resulting better
D–A interaction in B2/P2. The chemical shifts δ(CuN) =
112–116 ppm measured for the dicyanobenzene and dicyano-
pyrazine acceptor moieties are slightly downfielded compared
to donor substituted CEEs (δ(CuN) = 108–115 ppm)8c which
further confirms the aforementioned trends seen by the BLA.
The frequency of the stretching vibration of the CN group
showed very similar trends, as seen by the NMR. Namely, the
CuN stretching appeared generally at lower frequencies for
pyrazine series. Extension and (partial) planarization of the
π-linker (e.g. 1 vs. 2 or 3 vs. 4) shifted the CN wavenumber to
In contrast to the first oxidations, the first reductions of
chromophores in the series B and P were observed in a wide
range from −1.62 to −1.03 and −1.24 to −0.67 V, respectively.
The difference between the first reduction potentials of the
particular chromophores in both B and P series ranges from
0.36 to 0.44 V. This reflects a higher withdrawing ability of the
dicyanopyrazine moiety over the dicyanobenzene caused by
the presence of two electronegative nitrogen atoms. However,
when considering the dicyanobenzene/pyrazine acceptor as the
main reduction center and the same electron nature and
number of appended donors, the observed differences within
the particular series B or P must be elucidated as a conse-
quence of the π-linker. The first reduction potentials of the
chromophores in the series B or P gradually decrease and
become steady at about −1.10 and −0.70 V. When going from
the chromophore B1/P1 (one 1,4-phenylene moiety as a
π-linker) to B3/P3 (biphenyl π-linker) and B4/P4 (phenylethy-
nylphenyl π-linker), the first reduction potentials decrease
from −1.62/−1.24 to −1.48/−1.05 and −1.41/−0.97 V as a result
of the π-linker gradual extension. However, chromophores B2/
higher energy and became steady at around 2200/2190 cm−1
.
Electrochemistry
Electrochemical measurements of all chromophores B1–B10
and P1–P10 (ref. 10) were carried out under standard con-
ditions (N,N-dimethylformamide containing 0.1 M Bu4NPF6)
in a three electrode cell by cyclic voltammetry (CV) and rotat-
ing disk voltammetry (RDV). The working electrode was a plati-
num disc (2 mm in diameter) for CV and RDV experiments. As
the reference and auxiliary electrodes were used a saturated
calomel electrode (SCE) separated by a bridge filled with a sup-
porting electrolyte and a Pt wire, respectively. The acquired
data are summarized in Table 3, and representative CV dia-
grams of chromophores B2 and B10 are shown in the ESI
(Fig. S1–S2†).
All chromophores 1–10 in both series B and P showed two
close, mostly reversible, one-electron oxidation processes
(differences of about 100 mV measured by CV) that were, in
most cases, merged into one two-electron wave, as indicated
by RDV. This electrochemical behavior reflected the presence
of two equivalent N,N-dimethylamino donor groups appended
to the dicyanobenzene/pyrazine acceptor. The first oxidation
potentials of chromophores in both series B and P range from
+0.93 to +0.78 V and +1.02 to 0.81 V, respectively. As can be
seen, extension of the π-conjugated path affects the first
P2 bearing a shorter π-linker showed more positively shifted
oF
(red1)
E
up to −1.28/−0.87 V than extended chromophores B3/P3
and B4/P4. This can be attributed to partial extension of the
π-linker by an acetylene unit connected directly to the acceptor
and, in particular, to planarization of the entire π-systems. A
similar effect can be observed when comparing chromophores
B3/P3 and B5/P5 or B4/P4 and B6/P6. Hence, a separation of
the π-linker from the dicyanobenzene/pyrazine acceptor by the
linear ethynyl spacer plays a very crucial role and affects the
electrochemical behavior of X-shaped chromophores consider-
ably. In contrast to this, the first reduction of the chromophore
oF
(red1)
B7 (E
= −1.32 V) is significantly impeded by the propeller-
shape of the terphenyl linker. Except B7, chromophores B6/
P6–B10/P10 showed almost constant first reduction potentials
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which implies that a combination of two/three 1,4-phenylene chromophores shown in Fig. 2 are very similar. However, the
moieties in conjunction with acetylene units caused complete absorption maxima of P chromophores are generally batho-
isolation of the N,N-dimethylamino donor and the dicyano- chromically shifted, which again confirms the previous con-
benzene/pyrazine acceptor.
clusion on higher electron withdrawing character of the
The corresponding electrochemical gaps ΔE (Table 3) are dicyanopyrazine moiety. Chromophores B1/P1 and B2/P2
mainly affected by the variation in the first reduction poten- showed multiple CT-bands which reflects complex conjugated
oF
(red1)
tials and, therefore, mimic the same trends as seen for E
.
pathways between the particular N,N-dimethylamino donor
The lowest electrochemical gaps were recorded for chromo- and cyano acceptor. The spectra of chromophores B feature
phores B10/P10 with the largest and fully planar π-linkers (see more vibronic structure than those of chromophores P. When
also the energy level diagram below).
going from chromophore B1/P1 to B2/P2, thus extending and
planarizing the π-linker by one acetylene unit, the absorption
maxima were shifted by 48 and 28 nm (Table 4), respectively.
However, moving the acetylene unit between two 1,4-pheny-
lene units as in B4/P4 or further π-linker extension as in B6/P6
and B10/P10 led to disappearance of the CT-band and a pro-
nounced hypsochromic shift. This is in accordance with the
observation made by Nielsen et al.22 that an extension of the
π-system by more nonplanarly arranged 1,4-phenylene units
led to a blue-shift of the CT-band measured in a solvent.
However, this is also in contrast to gas phase measurement
excluding solvation and H-bonding in which a systematic red-
shift was observed. Hence, from B7 onwards, the CT-bands
were observed as hardly distinguishable shoulders and were
merged with the bands appearing at around 350 nm with
rising intensity. These bands probably correspond to the tran-
sition between the N,N-dimethylamino donor and the
extended electronegative π-linker. Thus, insertion of three 1,4-
phenylene units in combination with one or more acetylene
units can completely quench D–A interaction and none or very
weak CT-band is observed. These observations are in accord-
ance with the aforementioned electrochemical conclusions.
In contrast to all N,N-dimethylamino-substituted π-linkers,
which showed emission properties,19 only less extended chro-
mophores B1–B4 showed fluorescent behaviour (Table 4, the
ESI Fig. S5†). Moreover, the pyrazine chromophores did not
show any fluorescence at all. Thus, extension of the π-system
or attachment of a stronger acceptor moiety caused emission
disappearance and a gradual reduction of the fluorescence
quantum yield.
UV/Vis spectroscopy
Optical properties of all chromophores 1–10 were studied by
absorption and emission spectra. The positions of the longest-
wavelength absorption and fluorescence maxima λAmax and λmF ax
as well as the molar absorption coefficients ε and the fluo-
rescence quantum yields qF are given in Table 4. Representa-
tive UV/Vis spectra of selected chromophores are shown in
Fig. 2; for complete spectra listing see the ESI (Fig. S3–S4†). All
spectra were measured in CH2Cl2.
The absorption spectra of chromophores in series B and P
showed longest-wavelength absorption maxima (CT-bands)
appearing within the range of 335–458 and 354–499 nm,
respectively. The absorption spectra of representative B and P
Table 4 Optical properties of chromophores 1–10
ε [103 mol−1
dm3 cm−1
λFmax
[nm (eV)]
Compd
λAmax [nm(eV)]
]
qF
B1/P1
B2/P2
B3/P3
B4/P4
B5/P5
B6/P6
B7/—
B8/—
B9/P9
B10/P10
410(3.02)a/471(2.63)
458(2.71)a/499(2.48)
380(3.26)a/425(2.92)
378(3.28)a/433(2.86)
422(2.94)a/465(2.67)
424(2.92)/466(2.66)
335(3.70)/—
345(3.59)/—
342(3.63)/354(3.50)
362(3.43)/371(3.34)
12.82/23.18
18.98/24.73
19.05/25.83
30.29/30.38
26.66/35.52
33.99/36.81
53.73/—
75.96/—
84.51/87.26
75.55/93.31
548b
589b
640b
658b
—
—
—
—
—
0.79b
0.76b
0.52b
0.10b
—
—
—
—
—
—
—
a Observed as a shoulder. b Emission maxima/fluorescence quantum
yields of the chromophores in series B.
Fig. 2 Representative UV/Vis absorption spectra of chromophores B1/P1, B4/P4 and B2/P2, B6/P6, B10/P10 measured in CH2Cl2 (10−5 M).
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Table 5 Calculated electronic parameters and experimental hyperpolarizabilities of chromophores 1–10
Compd
μ [D]
EHOMO [eV]
ELUMO [eV]
ΔEHOMO–LUMO [eV]
β (AM1) [esu × 10−30
]
β (exp.) [pm V−1
]
B1/P1
B2/P2
B3/P3
B4/P4
B5/P5
B6/P6
B7/—
B8/—
B9/P9
B10/P10
8.56/9.91
9.74/11.89
9.67/9.07
10.43/10.69
10.77/11.49
11.48/11.3
10.9/—
11.3/—
10.89/11.38
11.78/11.27
−8.28/−8.40
−8.22/−8.33
−8.15/−8.28
−8.20/−8.23
−8.21/−8.32
−8.16/−8.38
−8.18/—
−0.92/−1.43
−1.07/−1.75
−1.18/−1.78
−1.31/−1.69
−1.47/−1.92
−1.55/−2.01
−1.53/—
7.36/6.97
7.15/6.58
6.97/6.50
6.89/6.54
6.74/6.40
6.61/6.37
6.65/—
6.55/—
6.55/6.15
6.47/6.22
245/349
649/942
375/408
681/787
809/956
1263/1444
867/—
1 268/—
1218/1484
1701/1912
—a/0.53
0.9/1.1
—a/0.6
—a/1.1
1.2/1.2
3.6/1.4
2.1/—
2.8/—
3.2/3.0
4.9/3.1
−8.16/—
−1.61/—
−8.11/−8.15
−8.11/−8.29
−1.56/−2.00
−1.64/−2.07
a Below noise level (see the ESI).
Calculations and NLO properties
The second-order optical nonlinearities of the newly syn-
thesized chromophores B1–B10 were also determined experi-
mentally by investigation of the Second Harmonic Generation
(SHG). The SHG experiment was performed with powdered
samples that were oriented by dc-electric field. The studies
were performed for the angles that gave the maximal SHG
output. A Nd-YAG laser (pulse duration 15 ns) was used as a
fundamental laser beam. Powdered BiB3O6 microcrystallites
with known parameters of the second order susceptibilities
were used as the reference samples. The experimental β coeffi-
cients along with the theoretical values are summarized in
Table 5. Both hyperpolarizabilities showed sufficiently good
correlation (see the ESI Fig. S8–S9†). Chromophores bearing
short and nonplanar arrangement of the π-linkers as in 1, 3
and 4 showed weak (P series) or no (B series) SHG behavior
(see also the SHG readouts in the ESI Fig. S10–S19†). From the
series of compounds 1–5, bearing up to two 1,4-phenylene and
Quantum-chemical calculations and simulation of NLO pro-
perties of all target chromophores were performed at the semi-
empirical level of theory with the AM1 method and with the
time-dependent Hartree–Fock (TDHF) calculations, respect-
ively. All the calculations were performed using the PCGAMESS
package. The calculated data such as the ground stated dipole
moment μ, energies of the HOMO and the LUMO and their
differences ΔE as well as β coefficients are presented in
Table 5.
The first oxidation/reduction potentials measured in DMF
were recalculated23 to the corresponding HOMO/LUMO ener-
gies and gaps (see also the ESI†) and were further compared
with the AM1 calculated values. Although both HOMO−LUMO
gaps differ in their absolute values (differences of 4.6–4.9 eV),
they tightly correlate in both series of compounds (see the ESI
Fig. S6–S7†). Hence, even though they are very time-efficient,
the used semi-empirical calculations are obviously capable of
properly describing the trends seen by the electrochemical
measurements and can be considered as a reasonable tool for
the electronic property description of chromophores 1–10.
Fig. 3a shows the energy level diagram derived from the
electrochemical measurements. This diagram nicely visualizes
the aforementioned trends, namely: (i) the principal changes
are observed in the LUMO, (ii) the LUMO is significantly
lowered when going from series B (in black) to P (in red), (iii)
the HOMO remains practically unchanged throughout the
whole series of compounds, (iv) from chromophores B6/P6
onwards, the LUMOs as well as the HOMO−LUMO gaps are
steady, (v) although it does not contain a large π-linker, the
chromophore B2 showed a significantly lowered LUMO level as
a result of its planar arrangement, (vi) in contrast, the chromo-
phore B7 showed significantly raised LUMO due to its twisted
π-linker, and (vii) the lowest HOMO−LUMO gaps were
measured/calculated for chromophores 9 and 10 that feature
the longest π-linkers. As expected, the visualizations of frontier
molecular orbitals for representative pairs of chromophores
B2/B10 and P2/P10 showed acceptor-centered LUMO and
donor-centered HOMO (Fig. 3b; for complete listing see the
ESI Fig. S20–29†). A significant charge-separation is being
observed when extending the π-system.
Fig. 3 Energy level diagram (a) and representative HOMO and LUMO
localizations in B2/B10 and P2/P10 (b).
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one acetylene units, chromophores B2/P2 are exceptional isolation of the N,N-dimethylamino donor and the dicyanoben-
(β(exp) = 0.9 and 1.1 pm V−1). Although B2/P2 contains only zene/pyrazine acceptor. Optical properties of the studied chro-
one 1,4-phenylene and one acetylene unit, they showed almost mophores are dominated by one or more CT-bands, which
the same nonlinear optical response as B5/P5 having one reflects multiple conjugated pathways between each N,N-di-
additional 1,4-phenylene moiety (β(exp) = 1.2 pm V−1). This methylamino and cyano groups. In general, chromophores in
must be elucidated as an effect of its planar arrangement. The the series P showed bathochromically shifted longest-wave-
effect of the planar π-system arrangement can be further length absorption maxima which reflect higher electron with-
demonstrated by chromophores B6 and B10 that showed drawing character of the dicyanopyrazine moiety. The
strong SHG behavior (β(exp) = 3.6 and 4.9 pm V−1), which can aforementioned structural changes in particular chromo-
be attributed to their extended and fully planarized π-linkers phores affect also their absorption spectra. Extension of the
(two/three 1,4-phenylene units separated by two/three triple π-system and isolation of the D and A parts of the X-shaped
bonds). Chromophores P1–P5, bearing the short π-linker and push–pull molecules led to a hypsochromic shift of the CT-
the stronger dicyanopyrazine acceptor, showed generally bands that are, from B7/P6 onwards, observed as a joint peak
higher nonlinearities than isolobal B1–B5. However, from B6/ at about 350 nm with large molar absorption coefficients. In
P6 onwards, the impact of the stronger acceptor diminished or contrast to P1–P4, chromophores B1–B4 showed also fluo-
even opposite and higher nonlinearities were measured for rescent properties that gradually decrease with the extension
chromophores in the B series. Hence, as the donor and the of the π-system.
acceptor of a given push–pull molecule become completely iso-
Quantum-chemical calculations further confirmed the
lated by a large π-linker, the NLO response is dictated not experimental data. In general, from the experiments and calcu-
solely by the ICT but also by the size of the molecule (the lations carried out for X-shaped molecules 1–10 we can con-
number of polarizable electrons).24
clude the following:
• replacement of the dicyanobenzene with the dicyanopyra-
zine acceptor affects the optoelectronic properties most signifi-
cantly (tuning by the LUMO)
Conclusions
• the HOMO of 1–10 remained almost unchanged indepen-
A new series of X-shaped push–pull molecules based on 4,5- dently of the size and structure of the π-linker
disubstituted benzene-1,2-dicarbonitrile has been synthesized.
• the HOMO is localized on the peripheral donors while the
Three compounds B1, B3 and B4 were obtained by twofold LUMO is placed on the acceptor units
Suzuki–Miyaura reactions, and seven target chromophores B2
• the LUMO can be further lowered by planarization of the
and B5–B10 with the π-linker separated from the acceptor by entire π-system (e.g. B2 vs. B7)
an additional triple bond were obtained by Sonogashira cross-
• a position of the acetylene unit within the π-linker plays
coupling. All compounds were compared with isolobal chro- also an important role (e.g. B4/P4 vs. B5/P5)
mophores P1–P10 based on 5,6-disubstituted pyrazine-2,3-
• π-linker bearing two acetylene units in combination with
dicarbonitrile and subsequent structure–property relationships two 1,4-phenylene moieties completely isolates A and D parts
were further evaluated. X-ray analysis revealed different spatial of X-shaped push–pull molecules
arrangements of both acceptor moieties and the appended
• the lowest HOMO−LUMO gap and the highest nonlineari-
N,N-dimethylamino-substituted π-linkers. The dicyanopyrazine ties have been measured/calculated for molecules B9/P9 and
core showed significant out of plane deformation while the B10/P10 with the largest π-system
dicyanobenzene remained almost fully planar. The extent of
• planar molecules (e.g. B2, B6 and B10) delivered a strong
the ICT has been studied by BLA (δr) and the Bird index (I6). SHG response
Both quantities indicated higher ICT in the P series of com-
• first-order hyperpolarizability β depends not only on the
pounds. This has been further confirmed by the 13C NMR and extent of the ICT but also on the number of polarizable elec-
IR spectra that showed higher electron saturation of the CN trons (length of the π-system).
group in dicyanopyrazine compounds. 13C NMR chemical shift
In view of the current interest in push–pull systems and
and the frequency of the stretching vibration of the CN group their wide applications mainly in NLO and DSSC (both cyano
have also been affected by the length, composition and spatial groups can be hydrolysed to well-anchoring carboxylic acid
arrangement of the π-linker. Electrochemical measurements functions),25 we believe that this structure–property study on
carried out by the CV and RDV confirm the observations made X-shaped molecules would serve as a useful guideline.
above. Principal changes were recorded in the first reduction
potential. Significantly positively shifted first reduction poten-
tials have been observed for compounds with fully planar
π-linkers connected to the acceptor moiety via triple bonds
(e.g. B2/P2, B6/P6 and B10/P10). All chromophores from B6/P6
Experimental section
onwards showed almost constant first reduction potentials For general information and synthesis of 11 see the ESI.† Full
which implies that a combination of two/three 1,4-phenylene spectral characterization of pyrazine chromophores P1–P10 is
moieties in conjunction with acetylene units caused complete given in our previous publication.10
5524 | Org. Biomol. Chem., 2014, 12, 5517–5527
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Paper
3
General procedure for Suzuki–Miyaura cross-coupling
= 8.4 Hz, 4H; 2 × Ph), 6.77 (d, J(H,H) = 8.4 Hz, 4H; 2 × Ph),
2.99 (s, 12H, 2 × N(CH3)2). 13C-NMR (100 MHz, 25 °C, CDCl3):
δC = 150.50, 145.79, 141.46, 135.81, 135.34, 129.94, 127.79,
4,5-Diiodobenzene-1,2-dicarbonitrile (152 mg, 0.4 mmol) and
an appropriate boronic acid or its ester (0.84 mmol, 2.1 eq.)
were dissolved in a mixture of THF–H2O (20 ml, 4 : 1). Argon
was bubbled through the solution for 15 min whereupon
[PdCl2(PPh3)2] (28 mg, 0.04 mmol) and Na2CO3 (89 mg,
0.84 mmol) were added and the reaction mixture was stirred at
65 °C for 12 h. The reaction was diluted with water (50 ml) and
extracted with CH2Cl2 (2 × 50 ml). The combined organic
extracts were dried (Na2SO4), the solvents were evaporated in
vacuo and the crude product was purified by column chrom-
atography (SiO2; indicated solvent system).
127.66, 126.37, 115.82, 114.19, 112.88, 40.70. IR (HATR): νmax
/
cm−1 = 2917, 2224 (CN), 1600, 1357, 1222, 1062, 814.
+
HR-FT-MALDI-MS (DHB) m/z: 518.2468 (M+), C36H30N4
requires 518.2465. Anal. Calcd for C36H30N4 (518.66): C 83.37,
H 5.83, N 10.80; Found C 83.64, H 5.74, N 10.51.
Chromophore B4. General procedure for Suzuki–Miyaura
cross-coupling with 4-[4-(N,N-dimethylamino)phenylethynyl]
phenylboronic acid pinacol ester18 (292 mg) gave 179 mg
(79%) of chromophore B4 as an orange solid. M.p. > 300 °C.
Rf = 0.85 (SiO2; CH2Cl2). 1H-NMR (400 MHz, 25 °C, CDCl3):
δH = 7.84 (s, 2H, 2 × ArH), 7.41–7.37 (m, 8H; 4 × Ph), 7.06 (d,
3J(H,H) = 8.4 Hz, 4H; 2 × Ph), 6.64 (d, 3J(H,H) = 8.8 Hz, 4H;
General procedure for Sonogashira cross-coupling
4,5-Diiodobenzene-1,2-dicarbonitrile (152 mg, 0.4 mmol) and 2 × Ph) 2.99 (s, 12H, 2 × N(CH3)2). 13C-NMR (100 MHz, 25 °C,
an appropriate terminal acetylene (0.84 mmol, 2.1 eq.) were CDCl3): δC = 150.46, 145.37, 136.41, 135.6, 133.05, 131.71,
dissolved in THF (20 ml) and Et3N (5 ml). Argon was bubbled 129.48, 125.04, 115.55, 114.62, 111.96, 109.58, 93.04, 86.93,
through the solution for 15 min whereupon [PdCl2(PPh3)2] 40.37. IR (HATR): νmax/cm−1 = 2961, 2202 (CN), 1596, 1521,
(28 mg, 0.04 mmol) and CuI (8 mg, 0.04 mmol) were added 1358, 1222, 1133, 814. HR-FT-MALDI-MS (DHB) m/z: 566.2466
and the reaction mixture was stirred at 60 °C for 24 h. The sol- (M+), C40H30N4 requires 566.2465. Anal. Calcd for C40H30N4
+
vents were evaporated in vacuo and the crude product was puri- (566.71): C 84.78, H 5.34, N 9.89; Found C 84.51, H 5.51,
fied by column chromatography (SiO2; indicated solvent N 9.73.
system).
Chromophore B5. General procedure for Sonogashira cross-
with
4′-ethynyl-N,N-dimethylbiphenyl-4-amine18
Chromophore B1.26 General procedure for Suzuki–Miyaura coupling
cross-coupling with 4-(N,N-dimethylamino)phenylboronic acid (186 mg) gave 165 mg (73%) of chromophore B5 as a dark red
1
pinacol ester18 (208 mg) gave 121 mg (83%) of chromophore solid. M.p. > 300 °C. Rf = 0.71 (SiO2; CH2Cl2–hexane 6 : 1). H–
B1 as a bright yellow fluorescent solid. M.p. > 300 °C. Rf = 0.80 NMR (400 MHz, 25 °C, CDCl3): δH = 7.91 (s, 2H, 2 × ArH), 7.60
1
3
(SiO2; CH2Cl2). H-NMR (400 MHz, 25 °C, CDCl3): δH = 7.71 (s, (s, 8H, 4 × Ph), 7.54 (d, J(H,H) = 8.8 Hz, 4H; 2 × Ph), 6.80 (d,
2H, 2 × ArH), 7.01 (d, J(H,H) = 8.8 Hz, 4H; 2 × Ph), 6.60 (d, 3J(H,H) = 8.4 Hz, 4H; 2 × Ph), 3.01 (s, 12H, 2 × N(CH3)2).
3
3J(H,H) = 8.8 Hz, 4H; 2 × Ph), 2.96 (s, 12H, 2 × N(CH3)2). 13C-NMR (100 MHz, 25 °C, CDCl3): δC = 150.61, 142.93, 136.22,
13C-NMR (100 MHz, 25 °C, CDCl3): δC = 150.30, 145.60, 135.58, 132.7, 131.13, 127.91, 127.53, 126.31, 118.86, 115.10, 113.83,
130.42, 125.83, 116.27, 112.84, 112.17, 40.42. IR (HATR): νmax
/
112.82, 101.43, 86.33, 40.64. IR (HATR): νmax/cm−1 = 2880,
cm−1 = 2920, 2223 (CN), 1607, 1522, 1361, 1261, 1093, 810. 2200 (CN), 1595, 1441, 1360, 1222, 1092, 811. HR-FT-MALDI-
HR-FT-MALDI-MS (DHB) m/z: 366.1834 (M+), C24H22N4
requires 366.1839. Anal. Calcd for C24H22N4 (366.47): C 78.66, Anal. Calcd for C40H30N4 (566.71): C 84.78, H 5.34, N 9.89;
MS (DHB) m/z: 566.2450 (M+), C40H30N4 requires 566.2465.
+
+
H 6.05, N 15.29; Found C 78.39, H 6.27, N 15.01.
Found C 84.38, H 5.19, N 9.66.
Chromophore B2. General procedure for Sonogashira cross-
Chromophore B6. General procedure for Sonogashira cross-
coupling with commercial 4-ethynyl-N,N-dimethylaniline coupling with 4-[(4-ethynylphenyl)ethynyl]-N,N-dimethylani-
(122 mg) gave 153 mg (92%) of chromophore B2 as an orange line18 (206 mg) gave 177 mg (72%) of chromophore B6 as an
solid. M.p. > 300 °C. Rf = 0.72 (SiO2; CH2Cl2–hexane 6 : 1). orange solid. M.p. > 300 °C. Rf = 0.76 (SiO2; CH2Cl2–hexane
1
1H-NMR (400 MHz, 25 °C, CDCl3): δH = 7.80 (s, 2H, 2 × ArH), 6 : 1). H-NMR (400 MHz, 25 °C, CDCl3): δH = 7.91 (s, 2H, 2 ×
7.46 (d, 3J(H,H) = 8.8 Hz, 4H; 2 × Ph), 6.66 (d, 3J(H,H) = 8.8 Hz, ArH), 7.53–7.48 (m, 8H, 4 × Ph), 7.43–7.40 (m, 4H; 2 × Ph), 6.66
3
4H; 2 × Ph), 3.03 (s, 12H, 2 × N(CH3)2). 13C-NMR (100 MHz, (d, J(H,H) = 8.4 Hz, 4H; 2 × Ph), 3.00 (s, 12H, 2 × N(CH3)2).
25 °C, CDCl3): δC = 151.19, 135.71, 133.68, 131.05, 115.49, 13C-NMR (100 MHz, 25 °C, CDCl3): δC = 150.64, 143.40, 136.35,
112.59, 111.92, 108.23, 102.91, 85.51, 40.32. IR (HATR): νmax
/
133.15, 132.11, 131.62, 131.00, 126.46, 120.22, 114.98, 114.29,
cm−1 = 2920, 2177 (CN), 1605, 1360, 1222, 1037, 808. 112.00, 100.86, 94.56, 87.41, 87.16, 40.39. IR (HATR): νmax
/
+
HR-FT-MALDI-MS (DHB) m/z: 414.1826 (M+), C28H22N4
cm−1 = 3004, 2206 (CN), 1608, 1525, 1356, 1222, 1130, 846,
requires 414.1839. Anal. Calcd for C28H22N4 (414.51): C 81.13, 814. HR-FT-MALDI-MS (DHB) m/z: 614.2470 (M+), C44H30N4
+
H 5.35, N 13.52; Found C 81.04, H 5.54, N 13.31.
requires 614.2465. Anal. Calcd for C44H30N4 (614.75): C 85.97,
Chromophore B3. General procedure for Suzuki–Miyaura H 4.92, N 9.11; Found C 85.50, H 5.01, N 9.21.
cross-coupling with 4′-(N,N-dimethylamino)biphenylboronic
Chromophore B7. General procedure for Sonogashira cross-
acid pinacol ester18 (272 mg) gave 180 mg (87%) of chromo- coupling with 4″-ethynyl-N,N-dimethyl-[1,1′:4′,1″-terphenyl]-4-
phore B3 as a yellow solid. M.p. > 300 °C. Rf = 0.78 (SiO2; amine10,19 (250 mg) gave 198 mg (69%) of chromophore B7 as
1
CH2Cl2). H-NMR (400 MHz, 25 °C, CDCl3): δH = 7.87 (s, 2H, an orange solid. M.p. > 300 °C. Rf = 0.60 (SiO2; CH2Cl2–hexane
2 × ArH), 7.49 (d, 3J(H,H) = 8.4 Hz, 8H; 4 × Ph), 7.16 (d, 3J(H,H) 3 : 1). H-NMR (400 MHz, 25 °C, CDCl3): δH = 7.95 (s, 2H, 2 ×
1
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ArH), 7.70–7.66 (m, 16H, 8 × Ph), 7.55 (d, 3J(H,H) = (9.2 Hz, Computational procedure
4H; 2 × Ph), 6.81 (d, 3J(H,H) = 8.8 Hz, 4H; 2 × Ph), 3.01 (s, 12H,
All calculations were performed with
a semi-empirical
2 × N(CH3)2). 13C-NMR (100 MHz, 25 °C, CDCl3): δC = 136.20,
135.73, 135.48, 133.73, 132.76, 127.62, 127.30, 40.08 (11
signals are missing). IR (HATR): νmax/cm−1 = 3003, 2203 (CN),
1652, 1418, 1361, 1222, 1092, 809. HR-FT-MALDI-MS (DHB)
AM1 method implemented in the PCGAMESS package.27 Com-
putational files were prepared and interpreted with the aid of
GABEDIT 2.4.6 (ref. 28) including the preparation of graphics.
+
m/z: 718.3088 (M+), C52H38N4 requires 718.3091. Anal. Calcd
for C52H38N4 (718.90): C 86.88, H 5.33, N 7.79; Found C 86.51,
H 5.22, N 7.62.
Acknowledgements
Chromophore B8. General procedure for Sonogashira cross-
coupling with 4′-[(4-ethynylphenyl)ethynyl-N,N-dimethylbiphe-
nyl-4-amine10,19 (270 mg) gave 211 mg (69%) of chromophore
B8 as an orange solid. M.p. > 300 °C. Rf = 0.79 (SiO2; CH2Cl2–
This research was supported by the Czech Science Foundation
(P106/12/0392). L. D. and F. B. are indebted to the Technology
Agency of the Czech Republic (TE01020022, Flexprint). M.R.
and F. B./M. L. are indebted to the Ministry of Education,
Youth and Sports of the Czech Republic (CZ.1.07/2.3.00/
30.0021 and LG13053). W. K. is grateful to the Balassi Institute
for financial support.
1
hexane 6 : 1). H-NMR (400 MHz, 25 °C, CDCl3): δH = 7.93 (s,
3
2H, 2 × ArH), 7.56–7.51 (m, 20H, 10 × Ph), 6.80 (d, J(H,H) =
8.8 Hz, 4H; 2 × Ph), 3.00 (s, 12H, 2 × N(CH3)2). 13C-NMR
(100 MHz, 25 °C, CDCl3): δC = 150.45, 136.34, 132.31, 132.13,
131.99, 130.93, 127.84, 126.21, 125.65, 120.98, 120.14, 114.90,
114.41, 112.89, 100.56, 93.27, 89.16, 87.30, 40.71 (2 signals are
missing). IR (HATR): νmax/cm−1 = 3004, 2202 (CN), 1590, 1418,
1361, 1221, 1093, 838, 812. HR-FT-MALDI-MS (DHB) m/z:
Notes and references
766.3062 (M+), C56H38N4 requires 766.3091. Anal. Calcd for
1 P. N. Prasad and D. J. Williams, Introduction to Nonlinear
Optical Effects in Organic Molecules and Polymers, Wiley,
New York, 1991.
+
C56H38N4 (766.95): C 87.70, H 4.99, N 7.31; Found C 86.95,
H 5.10, N 7.38.
Chromophore B9. General procedure for Sonogashira cross-
coupling with 4-[(4′-ethynylbiphenyl-4-yl)ethynyl]-N,N-dimethy-
laniline10,19 (270 mg) gave 220 mg (72%) of chromophore B9
as an orange solid. M.p. > 300 °C. Rf = 0.75 (SiO2; CH2Cl2–
2 For general reviews on NLO active compounds see:
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3 For general reviews on organic π-conjugated materials and
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M. E. Thompson, ed., Special issue on “Organic electronics
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(b) R. D. Miller and E. A. Chandross, ed., Special issue on
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and O. Pytela, Dyes Pigm., 2011, 90, 48–55.
1
hexane 3 : 1). H-NMR (400 MHz, 25 °C, CDCl3): δH = 7.93 (s,
2H, 2 × ArH), 7.65 (br s, 8H, 4 × Ph), 7.57 (br s, 8H, 4 × Ph),
7.41 (d, 3J(H,H) = 8.8 Hz, 4H; 2 × Ph), 6.66 (d, 3J(H,H) = 8.8 Hz,
4H; 2 × Ph), 2.99 (s, 12H, 2 × N(CH3)2). 13C-NMR (100 MHz,
25 °C, CDCl3): δC = 150.40, 142.24, 138.70, 136.33, 133.69,
132.99, 132.73, 131.03, 127.34, 127.04, 124.32, 120.62, 114.93,
114.21, 112.01, 109.96, 100.76, 92.39, 87.33, 86.65, 40.41. IR
(HATR): νmax/cm−1 = 2962, 2202 (CN), 1592, 1516, 1357, 1222,
1093, 821. HR-FT-MALDI-MS (DHB) m/z: 766.3121 (M+),
+
C56H38N4 requires 766.3091. Anal. Calcd for C56H38N4
(766.95): C 87.70, H 4.99, N 7.31; Found C 87.51, H 5.28,
N 7.08.
Chromophore B10. General procedure for Sonogashira
cross-coupling with 4-({4-[(4-ethynylphenyl)ethynyl]phenyl}-
ethynyl)-N,N-dimethylaniline10,19 (290 mg) gave 202 mg (62%)
of chromophore B10 as an orange solid. M.p. > 300 °C. Rf =
0.71 (SiO2; CH2Cl2–hexane 3 : 1). 1H-NMR (400 MHz, 25 °C,
CDCl3): δH = 7.93 (s, 2H, 2 × ArH), 7.55 (br s, 8H, 4 × Ph), 7.48
3
(br s, 8H, 4 × Ph), 7.40 (d, J(H,H) = 8.8 Hz, 4H; 2 × Ph), 6.65
3
(d, J(H,H) = 8.8 Hz, 4H; 2 × Ph), 2.99 (s, 12H, 2 × N(CH3)2).
13C-NMR (100 MHz, 25 °C, CDCl3): δ = 150.48, 136.36, 133.04,
132.16, 132.04, 131.78, 131.43, 130.89, 125.29, 124.93, 121.61,
121.26, 114.88, 114.47, 112.00, 109.74, 100.43, 93.45, 92.79,
87.43, 87.38, 40.41 (1 signal is missing). IR (HATR): νmax/cm−1
= 2920, 2202 (CN), 1609, 1591, 1523, 1360, 1122, 836, 818.
6 (a) W. Wu, C. Wang, C. Zhong, C. Ye, G. Qui, J. Qin and
Z. Li, Polym. Chem., 2013, 4, 378–386; (b) J. Zhu, C. Lu,
Y. Cui, C. Zhang and G. Lu, J. Chem. Phys., 2010, 133,
244503.
HR-FT-MALDI-MS (DHB) m/z: 814.3066 (M+), C60H38N4
+
requires 814.3091. Anal. Calcd for C60H38N4 (814.99): C 88.43,
H 4.70, N 6.87; Found C 88.68, H 4.48, N 7.02.
5526 | Org. Biomol. Chem., 2014, 12, 5517–5527
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