Multipodal arrangement of push-pull chromophores: a fundamental parameter affecting their electronic and optical properties

Article abstract of DOI:10.1039/c6nj02994a

A series of model push-pull molecules with linear, quadrupolar, and tripodal arrangements, a varyingly substituted amino donor, two acceptors, and a partially extended π-system has been prepared. Two peripheral electron acceptors, namely N,N′-dibutylbarbituric acid and dicyanovinyl, were employed. The fundamental properties of 24 push-pull chromophores were investigated by differential scanning calorimetry, electrochemistry, one-photon absorption spectroscopy, photoinduced piezooptics, and were supported by DFT calculations. Thorough structure-property relationships were elucidated, while a significant influence of the structural arrangement/branching on the electronic and optical properties has been revealed. The fundamental optoelectronic properties of push-pull molecules are affected by their arrangement (linear/quadrupolar/tripodal), the peripheral acceptor attached, extension and planarization of the π-system, and also by the type of auxiliary N-substituent.

Full text of DOI:10.1039/c6nj02994a

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PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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Journal Name
ARTICLE
Multipodal Arrangement of Push-Pull Chromophores:
A Fundamental Parameter Affecting Their Electronic and Optical
Properties
Received 00th January 20xx,
Accepted 00th January 20xx
M. Klikar,aI. V. Kityk,b D. Kulwas,b T. Mikysek,c O. Pytelaaand F. Bureš*a
DOI: 10.1039/x0xx00000x
A series of model push-pull molecules with linear, quadrupolar, and tripodal arrangement, variously substituted amino
donor, two acceptors, and partially extended π-system has been prepared. Two peripheral electron acceptors, namely
N,N´-dibutylbarbituric acid or dicyanovinyl, were employed. The fundamental properties of 24 push-pull chromophores were
investigated by differential scanning calorimetry, electrochemistry, one photon absorption spectra, photoinduced
piezooptics, and were completed by DFT calculations. Thorough structure-property relationships were elucidated, while a
significant influence of the structural arrangement/branching on the electronic and optical properties has been revealed.
The fundamental optoelectronic properties of push-pull molecules are affected by their arrangement
(linear/quadrupolar/tripodal), the peripheral acceptor attached, extension and planarization of the π-system, and also by
the type of auxiliary N-substituent.
www.rsc.org/
and bulk-heterojunction solar cells (BHJSCs).8 Push-pull
molecules showed also semiconducting properties9 with
prospective application in organic field-effect transistors
(OFETs).10 The increased popularity of organic push-pull
Introduction
In recent two decades, organic push-pull chromophores have
become very popular materials used in many areas of chemistry
and material sciences.1 However, their predominant and
historically most frequent application is in nonlinear optics
(NLO).2 Push-pull molecules can generally be designed towards
second- and third-order NLO. Whereas the first one is described
by second rank polar tensors and require macroscopic charge
density acentricity, third-order NLO is described by third rank
polar tensors, which, from a phenomenological point of view,
may occur both in centrosymmetrical and non-
centrosymmetrical media.3 Among several known nonlinear
optical effects, a particular attention is currently devoted to
third harmonic generation (THG), two and multi photon
absorption (2PA and MPA), electro-optic Kerr effect and
piezooptical effects.4 Beside common NLO applications, organic
push-pull chromophores are currently being used as two- or
multiphoton absorbers,5 active materials for the optical devices
such as organic photovoltaic cells (OPVCs),6 organic light-
emitting diodes (OLEDs),1d dye-sensitized solar cells (DSSCs),7
NLOphores results from their unique intrinsic properties.
A typical push-pull molecule is made of a -conjugated
backbone of multiple bonds ( -linker) end-capped with electron
donor (D) and acceptor (A) groups. This D- -A arrangement
enables effective charge transport between the given donor
and acceptor through the -linker, so-called intramolecular
charge transfer (ICT). The ICT strongly polarizes the whole D-
π
π
π
π
π
-
A system, increases its ground state dipole moment as well as
the difference of dipole moments between the ground and
excited states.11 Consequently, push-pull chromophores with
enhanced ICT possess higher microscopic hyperpolarizabilities,
however their further application is often restrained by a
limited stability with respect to laser power densities.12 Until
now, many
π-conjugated backbones, electron donors and
acceptors were utilized to build powerful push-pull systems
with enhanced NLO responses defined by their large
microscopic hyperpolarizability coefficients.13
Compared to inorganic materials, a dominant advantage of
organic push-pull systems can be seen in their facile and
relatively inexpensive/manifold synthesis, well-defined
structure, and tunable (opto)electronic properties. The latter
property tuning of fundamental parameters such as the
position of the longest-wavelength absorption maxima, the
HOMO-LUMO gap, and the dipole moment as well as solubility
and thermal stability can be achieved through a variation of the
a.Institute of Organic Chemistry and Technology, Faculty of Chemical Technology,
University of Pardubice, Studentská 573, Pardubice, 53210, Czech Republic.
b.Faculty of Electrical Engineering, Institute of Electronic Systems, Czestochowa
University of Technology, Armii Krajowej 17, Czestochowa, 42-201, Poland.
c. Department of Analytical Chemistry, Faculty of Chemical Technology, University
of Pardubice, Studentská 573, Pardubice 53210, Czech Republic.
Electronic Supplementary Information (ESI) available: [Synthetic details, CV curves,
UV/Vis absorptions spectra, DSC curves, DFT-derived HOMO/LUMO localizations,
data correlations and NMR spectra]. See DOI: 10.1039/x0xx00000x
particular part of the D-
π-A system (π-linker, donor, acceptor,
arrangement, planarity etc.).14
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Beside ordinary electron acceptors such as substituents with electrochemistry, UV/Vis absorption spectra, IR VsiepweAcrttircale,Oanlninde
–M and –I effects, more complex electron withdrawing moieties differential scanning calorimetry. DTOhI:e10.10p39h/oCt6oNinJ0d2u9c9e4dA
are also frequently being used. In this respect, dicyanovinyl piezooptics, a parametrical third order optical effect described
(DCV) is considered as a very powerful withdrawing group easily by fourth rank polar tensor, was also studied. The
introducible via Knoevenagel condensation of malononitrile photoinduction favors enhanced polarizabilities both of
with carbonyl compounds.15N,N'-Dialkylbarbituric acid (BA) electronic and phonon sub-system. The aforementioned
represents another heterocyclic, very robust, and powerful experimental data were further completed with the results
electron acceptor based on malonic acid.16
from DFT calculations.
On the other hand, the D-part of push-pull molecules very
often involves an amine group.14 N,N-Dialkylamino is
considered as one of the most efficient electron releasing group
used for the construction of linear push-pull molecules.17 Higher
multipodal chromophore arrangements such as quadrupolar
and octupolar are achieved on di- or triphenylamine (DPA and
TPA) donors. These central electron releasing moieties
equipped with peripheral DCV and BA acceptors showed to be
very powerful charge-transfer chromophores exhibiting strong
absorption and emission in the visible/near IR region of the
spectra, solvatochromic behavior, narrowed HOMO-LUMO gap,
and noticeable nonlinearities. These features predestinate
them as fluorophores for OLEDs, 2PA absorbers, ion sensors,
and probes for bio-imaging.18
Result and Discussion
Synthesis
In general, target compounds
1−24 were prepared by two
general pathways. The synthesis of chromophores with less
extended -linker without triple bond(s) utilizes aromatic
aldehydes 30 35. Whereas aldehydes 30 and 32 35 are
π
−
−
commercially available, aldehyde 31 was prepared from the
methyldiphenylamine 27. Its iodination using I2/AgNO3 system21
afforded both mono and diiododiphenylamines 28 and 29. This
inseparable mixture was further subjected to lithiation with
nBuLi at -78 °C and subsequent formylation with DMF providing
31 in 80% yield. The simultaneously formed aldehyde 33 was
Recently, our research group focused on model push-pull
molecules containing TPA central donor with various peripheral
cyano withdrawing units. These molecules showed remarkable
nonlinear optical properties, 2PA in particular.19 Within these
initial studies on very popular TPA derivatives, we have also
preliminarily focused on a branching effect. According to the
current state of the art, not much attention has been devoted
discarded as
chromophores
a
by-product (Scheme 1). The pairs of
10 13 14 17 18, and 21 22 were
1
/
2
,
5
/6
,
9
/
,
/
,
/
/
prepared via Al2O3 catalyzed Knoevenagel condensation of
aldehydes
30
−
35
with
malondinitrile
25
or
N,N´-dibutylbarbituric acid 26 in satisfactory yields 42
−94 %
(Scheme 2). The latter BA derivative was prepared according to
our procedure.16a,22,23 This facile reaction sequence provided
twelve variously arranged chromophores with two terminal
acceptors.
to
a comparison of push-pull molecules with linear,
quadrupolar, and tripodal arrangements built on an identical
N,N dialkyl(aryl)anilino donor.20 For these reasons, we report
herein a complex study that compares fundamental properties
of gradually branched push-pull molecules derived from TPA
and its amino analogues. Twentyfour model chromophores
The synthesis of chromophores
23 24 bearing an additional acetylenic spacer started with
preparation of extended aldehydes 49 54 (Scheme 1). These
aldehyds were synthesized by Sonogashira cross-coupling of the
corresponding iodo derivatives with propargyl alcohol 38
Iodination of alkyl(aryl)amines 27 36 and 39 with
I2/AgNO3(NaHCO3) system21,24 afforded compounds 28
29 37
and 40 42 in reasonable yields.
The degree of iodination was controlled by the amount of I2
used. Similarly to 28 29, mono and diiodotripehnylamines
40 41 were obtained as inseparable mixtures, which however
3, 4, 7, 8, 11, 12, 15, 16, 19,
20
,
,
−
1
−
24 (Fig. 1) with systematically altered structure were
designed, synthesized, and further investigated to thoroughly
elucidate structure-property relationships. Chromophores 24
possess systematically extended -conjugated system, altered
.
,
,
1
−
−
,
π
−
acceptor, and increased degree of branching (multipodality).
−
−
smoothly underwent Sonogashira reaction with 38 under
standard catalytic conditions (Pd(PPh3)2Cl2, CuI, and Et3N)25 to
afford alcohols 46
alcohols 43 48 were easily separable by column
chromatography and could be subsequently oxidized to
aldehydes 49 54 in 59-83% yields by using Dess-Martin
−47 in the yields of 68-70 %. All prepared
−
−
reagent.26 The final step was again Al2O3-catalyzed Knoevenagel
condensation with 25 and 26 providing all remaining
chromophores. It should be noted, that Knoevenagel reaction
Figure 1. Target molecules 1−24 with linear, quadrupolar, and tripodal arrangements.
on extended aldehydes 49
generally higher yields than the reaction on arylaldehydes
30 35. The experimental details and spectral characterizations
−54 proved to be facile and gave
Whereas N,N-dialkyl(aryl)-anilines were used as electron
donors, malononitrile 25 and N,N´-dibutylbarbituric acid 26 act
as electron withdrawing moieties. The impact of these
−
of all intermediates 28−29, 31, 37, and 40−54 are given in the
ESI.
structural changes in
1−24 were investigated by
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Scheme 1. Synthetic pathways towards desired aldehydes 31 and 49-54. Dess-
Martin reagent = 1,1,1-tris(acetyloxy)-1,1-dihydro-1,2-benziodoxol-3-(1H)-one.
Scheme 2. Final Knoevenagel condensation giving target chromophores 1-24.
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According to the structural features of chromophores
we can divide them into the following sub-groups:
1
−
24
,
•
•
Compared to BA derivatives, DCV-terminated molecules
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DOI: 10.1039/C6NJ02994A
showed higher melting points and temperatures of
•
chromophores with DCV (odd numbers) or BA (even
numbers) acceptor unit,
decomposition.
A
very significant reduction of the decomposition
•
chromophores with (
3
,
4
,
7
,
8
,
11
,
12
,
15
,
16
17
,
19
18
,
20
21
,
23
22
,
temperature of about 100−200 °C was encountered for
24) or without (
1
,
2
,
5
,
6
,
9
,
10
,
13
,
14
,
,
,
,
)
derivatives with an additional acetylenic spacer
(decomposition occurred either immediately or shortly
after the melting).
additional acetylenic spacer linked to the acceptor,
chromophores with various degree of branching: linear
12), quadrupolar (13 20), and tripodal (21 24).
In addition, molecules 12 and 13 20 possess systematically
•
(1
−
−
−
•
The chromophores without triple bond(s) are stable even
in a liquid state.
1
−
−
varied substituents appended to the amino donor (Me or Ph), Hence, the highest melting point and temperature of
which would also affect the donor strength and overall decomposition were measured for linear , quadrupolar 17 and
-linker without triple
9
extension of the
π
-system.
tripodal 21 bearing DCV acceptor moiety, π
bonds and TPA central unit.
Thermal properties
Thermal behaviour of compounds
differential scanning calorimetry (DSC). Figure
thermograms of three representative compounds
1
−
24 was studied by
shows
12, and 24
2
7
,
while Table 1 lists all the measured melting points (Tm) and
temperatures of thermal decompositions (Td). For all DCS curves
see the ESI. The measured melting points of
108 to 226 °C and the temperature of decomposition was
estimated within the range of 115 396 °C. Compound
1−24 range from
−
1
provided very sharp peak of melting/crystallization at
182/147 °C and subsequent evaporation accompanied by the
partial decomposition at 332 °C. Compound
behaviour but a complete evaporation at 434 °C with partial
decomposition at 392 °C was observed. For chromophore , the
9 exhibited a similar
2
Figure 2. Representative DSC curves of compounds 7, 12, and 24 determined with
a scanning rate of 3 °C/min under N2.
sharp peaks of melting (163 °C), crystallization (148 °C), and
decomposition (258 °C) were preceded by moisture/solvent
desorption at 100
very gradual decomposition within the range of 70 °C followed
by their melting. For 15, and 19, the melting process was
−120 °C. Compounds 3, 8, 11 and 12 showed
Electrochemistry
4, 7,
Electrochemical measurements of chromophores
1−24
terminated by an immediate rapid decomposition. The
endothermic glass transition about 220 °C and a typical
were carried out in N,N-dimethylformamide containing 0.1 M
Bu4NPF6 in a three electrode cell by cyclic voltammetry (CV),
rotating disk voltammetry (RDV), and polarography. The
working electrode was platinum disk (2 mm in diameter) for CV
and RDV experiments. Saturated calomel electrode (SCE)
separated by a bridge filled with supporting electrolyte and Pt
wire were used as reference and auxiliary electrodes. All
potentials are given vs. SCE. The acquired data are summarized
exothermic decomposition of compounds
6 and 14 was
observed, however their decomposition was also accompanied
by an endothermic curving induced probably by their intensive
evaporation. For chromophores 13 and 14, a typical monotropic
solid-solid transition of metastable crystals was observed at 195
and 120 °C. The relatively weak and broad endothermic peaks
in the range of 55−80 and 105−125 °C were recorded for 16, 20,
22 23, and 18, respectively. These extended chromophores
in Table 1, representative CV diagrams of compounds 9, 10 and
,
18 are given in the ESI.
proved difficult to crystallize and rather represent solidified
glassy materials. Hence, the wide peaks most likely represent a
glass or solid-solid transitions. On the contrary, compound 24
showed a very sharp peak of decomposition at 174 °C.
In summary, we can deduce the following outcomes from
the DSC measurements:
The half-wave potentials of the first oxidation and reduction
(E1/2(ox1) and E1/2(red1)) were found within the range of 0.98 to
1.40 and −1.29 to −0.75 V, respectively. The first oxidation and
reduction are typical one-electron processes, followed by
subsequent oxidations and reductions, and are obviously a
function of the used acceptor and donor, chromophore
•
Chromophore branching reduces its capability to
crystallize (especially for those bearing BA acceptor unit
with long aliphatic butyl chains).
arrangements as well as nature of the π-linker (Table 1).
•
Some of the quadropolar and most tripodal chromophores
showed glass or solid-solid transitions followed by
decomposition without melting.
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Table 1. Summary of thermal, electrochemical, linear and nonlinear optical properties of 1−24.
a
b
c
c
e
e
A f
A f
Tm
Td
E1/2(ox1)
E1/2(red1)
∆E c
EHOMO
ELUMO
λmax
εmax
PO·10-14 g
Compound
(°C)
182
163
131
143
115
142
185
119
139
108
178
126
206
134
182
-
(°C)
332
258
139
149
346
286
187
127
392
357
184
138
340
277
189
115
396
260
201
153
373
281
182
174
(V)
(V)
(eV)
(eV)
(eV)
(nm/eV)
433/2.86
461/2.69
479/2.59
503/2.47
432/2.87
460/2.70
474/2.62
497/2.49
442/2.81
468/2.65
481/2.58
501/2.48
468/2.65
486/2.55
488/2.54
509/2.44
475/2.61
503/2.47
497/2.49
517/2.40
460/2.70
496/2.50
483/2.57
509/2.44
(M-1·cm-1)
(m2/N)
1
2
1.11
1.02
1.03
0.98
1.17
1.10
1.13
1.06
1.21
1.15
1.15
1.12
1.29
1.16
1.33
1.14
1.33
1.20
1.25
1.18
1.38d
1.26
1.40d
1.20
−1.29
−1.19
−0.93
−0.90
−1.22
−1.09
−0.91
−0.86
−1.13
−1.03
−0.88
−0.83
−0.96
−0.92
−0.81
−0.78
−0.97
−0.92
−0.79
−0.77
−0.92d
−0.89
−0.75d
−0.75
2.40
2.21
1.96
1.88
2.39
2.19
2.04
1.92
2.34
2.18
2.03
1.95
2.25
2.08
2.14
1.92
2.30
2.12
2.04
1.95
2.30
2.15
2.15
1.95
−5.54
−5.45
−5.46
−5.41
−5.60
−5.53
−5.56
−5.49
−5.64
−5.58
−5.58
−5.55
−5.72
−5.59
−5.76
−5.57
−5.76
−5.63
−5.68
−5.61
−5.81
−5.69
−5.83
−5.63
−3.14
−3.24
−3.50
−3.53
−3.21
−3.34
−3.52
−3.57
−3.30
−3.40
−3.55
−3.60
−3.47
−3.51
−3.62
−3.65
−3.46
−3.51
−3.64
−3.66
−3.51
−3.54
−3.68
−3.68
58450
59200
48550
37650
48250
46750
45050
31500
30600
25350
37550
36450
40100
40250
46750
50050
49650
51350
51100
53600
89700
68250
88600
77850
3.01
3.18
3.30
3.93
2.81
3.06
3.16
3.90
3.15
2.86
3.01
3.12
3.19
3.09
3.15
3.16
3.21
3.32
3.16
4.13
3.20
3.14
3.12
3.35
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
226
-
195
-
218
-
-
-
a
b
Tm = melting point (the point of intersection of a baseline before the thermal effect with a tangent). Td = thermal decomposition (pyrolysis in N2 atmosphere).
c E1/2(ox1) and E1/2(red1) are half-wave potentials of the first oxidation and reduction, respectively; all potentials are given vs. SCE; ∆E = E1/2(ox1) - E1/2(red1); scan rate 100 mV.s-1 for CV.
d
e
f
Only peak potentials, RDV records can´t be evaluated due to inhibition of the electrode. –EHOMO/LUMO
= E1/2(ox1/red1) + 4.429 (Ref. 27). Measured in CH2Cl2.
g Maximally achieved photoinduced piezooptic coefficients at cw He-Ne laser probing wavelength 1150 nm. The data are presented with corrections on scattering background.
Whereas the first oxidation takes place predominantly on the
amino donor, the first reduction is mostly situated on the DCV
21
affects both HOMO and LUMO levels for linear molecules
and similarly, its impact on the LUMO of branched
molecules is diminished. Hence, the LUMO levels of 13 14
and 21 22 are almost identical and the principal changes
are seen on the HOMO.
Extension of the -linker by an additional electronegative
acetylenic spacer is accompanied by a similar reduction of
the E as seen for the DCV BA replacement. This is
demonstrated in Figure 3c for 11 17 19, and 21 23
/22 (tripodal). Whereas the acceptor replacement
or BA acceptors and the adjacent
π
-linker. The measured half-
1
2
wave potentials were further recalculated to the energies of the
HOMO and the LUMO (Table 1).27 From the measured
/
/
electrochemical data of
1−24, we can draw the following
conclusions and structure-property relationships:
•
π
•
When going from linear to quadrupolar and tripodal
chromophores, the first oxidation/reduction potentials
shift steadily to more positive values. In general,
chromophore branching/multipodality (number of the
acceptors attached to the central amino donor) does not
affect the absolute values of the HOMO-LUMO gap (e.g.
∆
→
9
/
,
/
/
.
However, in contrast to the aforementioned variation of
the acceptor, the HOMO becomes steady with increased
number of branches and the HOMO-LUMO gap is mostly
dictated by the LUMO.
ΔE of 1.95 eV for 12, 20, and 24, Figure 3a). The branching
shifts the HOMO and LUMO levels more deeply instead!
Replacement of the DCV by BA acceptor is accompanied
by a decrease/increase of the first oxidation/reduction
potentials, respectively. Energy level diagram in Figure 3b
illustrates impact of both acceptors on pairs of
•
Auxiliary substituents attached to the amino donor (Me or
•
Ph) affect the electrochemical behaviour of
similar way as branching. Energy level diagram for
chromophores , and 10 shown in Figure 3d depicts
their almost identical gap (
lowered HOMO/LUMO levels.
1−24 in a very
2, 6
∆
E ~ 2.2 eV) and gradually
chromophores
1/2 (linear), 13/14 (quadrupolar), and
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corresponding linear
of
the
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chromophore’sDeOxI:c1i0te.1d039s/tCa6tNe,J0w29h9i4lAe
the third one is located on the high-
energy side and is predicted to have
zero oscillator strength. As a result,
tripodal molecules 21−24 showed one
intense CT-band with the position
ranging from 460 to 509 nm.
• Hence, when going from linear to
quadrupolar and tripodal
chromophores, the CT-bands can be
either single or structured with
increased
molar
absorption
coefficient (e.g. from 10 to 21 is
∆
εmax
equal to 64350 M-1cm-1). The position
of the longest wavelength absorption
maxima is affected only negligibly
(Figure 4a).
•
A clear trend of bathochromically
shifted CT-band of BA over DCV
substituted chromophores, has been
encountered across all structural
arrangements. A red-shift of about
Figure 3. Energy level diagrams illustrating effect of branching/multipodality (a),
impact of the acceptor (b), extension of the -system (c), and auxiliary
N-substituent (d).
π
20
−
40 nm can be seen in the pairs of molecules differing
only in the acceptor unit (Figure 4b).
•
Compared to DCV-substituted chromophores, attaching
stronger electron withdrawing BA unit to linear and
tripodal chromophores reduces their molar absorption
coefficients. This is in contradiction to quadrupolar
molecules (Figure 4b).
The aforementioned observations imply that the electro-
chemical behaviour of 24 can be systematically tuned both in
1
−
terms of its absolute value (∆E) as well as frontiers of the gap
(EHOMO and ELUMO).
•
•
Extension and planarization of the chromophore
π
-backbone via an additional triple bond enhances the ICT
which is reflected by a red shift of the max by about 20 40
nm for the given pair of molecules (Figure 4c).
Replacement of the auxiliary substituents attached on the
amino donor has only diminished effect on max, especially
for the linear molecules 12 (Figure 4d). However, the
effect of N-substituent increases when going to
quadrupolar chromophores 13 20 or when extending the
-system by acetylenic unit (e.g. 13 vs. 17 and 16 vs. 20
One photon absorption
λ
−
All target chromophores 1−24 are intensely coloured solids
with a colour ranging from yellow to purple. Hence, linear
optical properties were examined by UV-Vis spectroscopy.
Some chromophores showed very weak fluorescence, most of
them none (especially those with BA acceptor), and, therefore
λ
1
−
emission properties of
1
−24 were not investigated. The longest-
−
wavelength absorption maxima
λ
max as well as molar absorption
π
,
coefficients εmax are summarized in Table 1. All absorption
spectra are found in the ESI. The longest-wavelength absorption
maxima λmax range from 432 nm to 517 nm with the molar
absorption coefficients εmax of 25−
90×103 M-1cm-1. In a similar
way as above, fundamental structure-property relationships
can be elucidated:
Table 1).
In general, the measured optical properties confirm the
conclusions made from electrochemical measurements. Both
electrochemical and optical gaps showed tight correlation (see
the ESI).
•
Linear chromophores 1−12 exhibited always one CT-band,
which position range from 432 to 503 nm.
•
The absorption spectra of quadrupolar chromophores
13−20 showed two peaks. Beside the main peak (468−517
nm), a shoulder located on the high-energy side of the
main peak (~400 nm) is observed. This splitting results
from the coupling between branches and can be explained
by the Frenkel exciton model.19d
•
Accordingly, the absorption spectra of tripodal molecules
should exhibit three bands (excited states). However, the
two states are degenerated and lie at the low-energy side
6 | J. Name., 2012, 00, 1-3
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variation in the dipole moment i.e. the
View Article Online
DOI: 10.1039/C6NJ02994A
difference between the first excited (1) and
higher (2) states; E01 is energy of transition
between ground (0) and first excited (1)
states; E12 is energy of transition between
first (1) and higher (2) excited states
including the phonon states; ∆µ1 is dipole
moment difference between the ground
state and the lowest charge transfer
excited-state. The photoinduced external
fields do not disturb substantially the
excited states and interacts mainly with the
ground state dipole moments and vary their
polarizabilities. So this explains why the role
of the ground state dipole moments is
prevailing here.
The particular chromophores 1−24 were
embedded into the PVA polymer matrices
and were grown in a form of films with
thickness about 1−3 µm by spin coated
technique similarly to described in the Ref.29
The optimal concentration with respect to
piezooptical response of the chromophore
(giving maximal piezooptical response) was
varied within the 10−15 mol%. The samples
were explored at different points of the
surfaces to avoid space non-homogeneity in
Figure 4. UV-Vis spectra (2×10-5 M sol. in CH2Cl2) of selected chromophores
illustrating effect of branching/multipodality (a), impact of the acceptor (b),
the chromophore distribution. To achieve the required accuracy
of the data the statistical evaluations were carried out in more
than 20 different points of the specimen. The susceptibility of
the method is enhanced during use of additional photo-
treatment as was described in the Ref.30 For this reason we have
performed additional photopolarization of the samples using
three types of photoinduced treatments as presented in Figure
5. The photoinduced measurements of the piezooptics at 1150
nm probing cw He-Ne laser were conducted for angles between
two photoinducing coherent Er:YAG beams varying within
extension of the π-system (c), and auxiliary N-substituent (d).
Piezooptical effect
Generally, the piezooptical (elasto-optical) effect is
described by fourth rank polar tensors (πijkl). The effect is caused
by the changes of birefringence ∆nij under applied mechanical
stress second order tensors:
∆nij = π ijkl σ kl
(1)
15
−
42 degrees. Maximal changes of piezooptical coefficients
where σkl is the second order stress tensor. The components i
and j define polarizations of the birefringence in the i and j
directions; k and l define the applied mechanical stress
directions. Contrary to similar third-order nonlinear optical
effects (2PA or THG), the piezooptics depends both on
were obtained for incident angle varying within 22
−26 °. Light
polarization does not play crucial role here. The photoexcitation
was performed for the single 1540 and 770 nm coherent laser
beams of Gaussian profile as well as during the simultaneous
excitation by these two beams. All the piezooptical monitoring
was performed using probing 20 mW cw He-Ne laser at
1150 nm and employing Senarmont method and stabilized high
sensitive photomultiplier. These measurements showed the
maximal piezooptical enhancement for photoexcitations by
1540 nm laser beam, less for the excitations at 1540 nm and 770
nm and after for excitations by the 770 nm. So one can conclude
that the photoexcitation is spectrally sensitive which confirms
the role of the particular interface states on the borders
polymer-chromophore. The occurrence of photoinduced
thermal changes leads to enhanced photo-thermal effect.
However, maximal magnitude of piezooptics was observed
when temperature of the samples was increased less than 3 K.
The processes are completely reversible with relaxation times
electronic
and
phonon
(vibration)
contributions.
Simultaneously, the ground state dipole moments and spectral
positions of the first UV absorption maxima play principal role.
Additional photoinduced changes favour further enhancement
of the elasto-optics.28 Hence, its relation to the microscopic
third order optical nonlinearities is not trivial. The third NLO
response with a simplified semi-empirical three-band approach
defining the third-order optical constants is described by a
fourth rank hyperpolarizability tensor γtijkl
:
µ021
(
µ122 + ∆µ12
)
Γ
γitjkl
2
(
E01 −0.5E02
)
(2)
where µ01 is variation of the dipole moment i.e. the difference
between the first excited (1) and ground (0) states; µ12 is
equal to about 5
−8 s. Taking into account the scattering
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Journal Name
Quantum chemical calculations
processes, the piezooptical coefficient does not change the
values of the corresponding magnitudes more than 3.5 %.
Figure 5 depicts principal experimental changes of the
photoinduced piezooptics for the composites measured by a
method similar to that described in the Ref.31, maximally
achieved photoinduced piezooptic coefficients are listed in
Table 1. From the data presented in Table 1 and Figure 5 we can
deduce the following structure-property relationships:
View Article Online
DOI: 10.1039/C6NJ02994A
Spatial and electronic properties of linear, quadrupolar and
tripodal chromophores
1−24 were investigated by DFT
calculations using Gaussian W09 package.32 Initial geometries
were estimated by PM3 method implemented in ArgusLab33
and these were subsequently optimized by DFT B3LYP/6-
311++G(2d,p) method. Energies of the HOMO and the LUMO,
their differences, and ground state dipole moments were
calculated with the DFT B3LYP/6-311++G(2d,p). A replacement
•
Within the series of linear molecules
generally increase from , and
-system and replacement of DCV by
1
−
12, the PO
1
−4
,
5
−8
9−12 as a result of
of the butyl substituents in N,N´-dibutylbarbituric moiety (16
,
the extension of the
BA acceptors.
π
18, 20, 22, and 24) by methyl groups has been made to
accelerate the DFT calculations. This substitution has almost
zero influence on the electron density distribution along the
•
A comparison of linear chromophores 4, 8, and 12 with the
highest POs reveals rather detrimental effect of the
chromophore extension via auxiliary N-substituents. The
PO decrease in the following order of substituents: diMe >
PhMe > diPh.
molecule. The first and second hyperpolarizabilities
β and γ
were deduced from the optimized geometries by employing
PM7 method implemented in MOPAC2012.34 All calculated data
are summarized in Table 2.
•
A monotonous increase of the POs can be seen when
going through the series of quadrupolar chromophores
The calculated energies of the HOMO/LUMO of 1−24 range
from 6.75/ 5.65 to 3.88/ 2.42 eV. Both energies correlate
−
−
−
−
13−20. Chromophore 19, which showed exceptionally
high calculated ground state dipole moment (see below),
is an exception.
with the experimental HOMO/LUMO levels obtained from the
electrochemical measurements (see the ESI). Hence, the used
DFT method can be considered as a reasonable tool for the
•
•
Chromophore 20 with two BA acceptors and extended
description of electronic properties of 1−24. The calculated
HOMO-LUMO gaps ( EDFT) range from 3.45 to 2.61 eV and
π
-system showed the highest PO of 4.13×10-14 m2/N.
A very similar trend can also be observed within tripodal
molecules 21 24 with the largest PO measured for 24
Similarly to electrochemical and optical properties, the
piezooptical effect in 24 is affected mostly by the
chromophore arrangement, electron withdrawing nature of the
appended acceptor unit, extension of the -linker, and type of
the auxiliary N-substituent. Hence, the largest POs within the
particular series were measured for chromophores 12 20
and 24
∆
correlates well with the experimentally obtained
electrochemical and optical gaps (see the ESI). Similar trends as
deduced from the electrochemistry and electronic absorption
spectra can also be seen from the calculated data. Namely,
-
.
1
−
∆
EDFT depends primarily on the branching, character of the
acceptor, -linker extension/planarity as well as auxiliary
N-substituent. Whereas extension of the -linker by an
additional acetylenic spacer affects the gaps very significantly
(e.g. vs. or 10 vs. 12, Table 2), replacement of the peripheral
acceptor DCV BA has diminished effect (e.g. vs. or 11 vs.
π
π
π
4
/8
/
,
,
.
1
3
→
1
2
12). In contrast to electrochemical measurements, the
calculated gaps steadily decrease when going from linear to
quadrupolar and tripodal systems with the largest one being
calculated for
The HOMO and LUMO localizations in representative
chromophores 13 19 and 24 are shown in Figure 6. For
1 and the lowest one for 23/24.
9
,
,
complete listing see the ESI. Figure 6 shows clear charge
separation and thus confirm ICT character of chromophores
1−24. As a general trend, the HOMO as well the HOMO−1 is
localized on the amino donor and the adjacent alternating
positions of the phenyl ring(s), whereas the LUMO is spread
over the peripheral DCV or BA acceptor(s) and the adjacent
π
1
-linker. This holds true especially for linear chromophores
12 In quadrupolar molecules 13 16 are the
1 localized on the central amino donor and
−
.
−
HOMO/HOMO
−
adjacent phenyl ring of the first branch, whereas the LUMO is
spread over the second branch. The LUMO+1 occupy the first
Figure 5. Dependence of the effective off-diagonal piezooptic coefficient PO at
wavelength 1150 nm of cw He-Ne laser for different samples at three different
regime of treatment: red color - 1540 nm two coherent nanosecond laser beams;
green - 770 nm two coherent nanosecond pulsed 770 nm laser beam; blue - 1540
nm + 770 nm bicolor coherent laser beam treatment.
branch. In quadrupolar molecules 17
LUMO situated on both branches. Tripodal chromophores
21 24 possess the LUMO spread over one or two particular
−20 with TPA donor is the
−
branch(es), while the third branch is occupied by the LUMO+1.
8 | J. Name., 2012, 00, 1-3
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ARTICLE
View Article Online
DOI: 10.1039/C6NJ02994A
Table 2. DFT calculated properties of chromophores 1−24.
b
β b
γ b
(×10-39
β
a
a
a
a
Comp EHOMO
ELUMO
∆EDFT
µa
Comp
.
EHOMO
ELUMO
∆EDFT
µa
γ b
(×10-29
esu)
3.28
3.06
5.04
4.72
3.41
2.70
5.16
4.90
4.80
2.44
6.20
5.59
(×10-29
.
(eV)
(eV)
(eV)
(D)
(eV)
(eV)
(eV)
(D)
(×10-39 esu)
esu)
esu)
1
2
−6.10
−5.82
−5.97
−5.71
−6.09
−5.82
−5.96
−5.72
−5.96
−5.72
−5.87
−5.65
−2.65
−2.42
−2.99
−2.74
−2.67
−2.46
−3.00
−2.77
−2.83
−2.62
−3.14
−2.90
3.45
3.40
2.98
2.97
3.42
3.36
2.96
2.95
3.13
3.10
2.73
2.75
11.53
7.62
55350
13
14
15
16
17
18
19
20
21
22
23
24
−6.53
−6.02
−6.32
−5.96
−6.41
−6.00
−6.22
−5.90
−6.75
−6.16
−6.49
−6.05
−3.56
−3.10
−3.65
−3.32
−3.48
−3.13
−3.58
−3.28
−3.78
−3.28
−3.88
−3.42
2.97
2.92
2.67
2.64
2.93
2.87
2.64
2.62
2.97
2.88
2.61
2.63
3.39
4.32
9.75
5.55
9.30
4.04
14.05
4.45
5.84
0.65
7.75
1.12
2.27
2.08
3.92
3.81
2.93
2.20
4.92
5.03
0.27
0.43
0.29
0.44
221961
183453
596987
617470
287712
293088
571624
743544
363524
410994
861877
1033629
69718
3
12.52
8.78
149186
168758
104914
121188
196459
219360
179186
162357
302020
330064
4
5
11.66
7.46
6
7
12.57
8.39
8
9
10.66
6.16
10
11
12
11.33
6.95
a Calculated at the DFT B3LYP/6-311++G(2d,p) level. b Calculated by MOPAC2012.
The HOMO as well the HOMO−1 remained on the central amino
acceptor. This is a common feature of tripodal molecules based and
on TPA.35
Molecular second and third order optical nonlinearities
were calculated and are presented in Table 2. As can be
seen, both polarizabilities showed reversal trends. Whereas
coefficients generally decrease with the chromophore
branching/symmetrization, the values of steadily increase
when going from 24. Moreover, the calculated third order
β
γ
β
γ
1
−
polarizabilities mimic the trends seen for experimentally
obtained POs (compare Figures 5 and S49 in the ESI). Namely,
the third order NLO response significantly increases with
chromophore branching, extension of the π-system and less by
the acceptor replacement and type of the auxiliary
N-substituent.
Conclusions
A series of 24 mostly new model push-pull chromophores
has been synthesized employing iodination, Sonogashira cross-
coupling reaction, and final Knoevenagel condensation. These
chromophores systematically vary in spatial arrangement
(linear
withdrawing nature of the peripheral acceptor (DCV vs. BA),
extension of -system, and type and number of methyl/phenyl
1−12, quadrupolar 13−20, and tripodal 21−24),
π
groups attached to the amino donor. A thorough elucidation of
the structure-property relationships has been performed based
on thermal, electrochemical, UV-Vis absorption, and
piezooptical data further supported by DFT calculations.
Figure 6. HOMO/HOMO
,
−1 (red) and LUMO/LUMO+1 (blue) localizations in 13 and
19 and 24.
HOMO/LUMO mix in
9
Structural features such as branching, DCV
replacement, and insertion of acetylenic units have detrimental
effect on thermal stability of 24. The branching does not
→BA
The calculated ground state dipole moments (Table 2) range
from 6 to 12.5 D for linear molecules 12 and are generally less
for quadrupolar chromophores 13 20 (except 19). Tripodal
1
−
1
−
−
affect the absolute values of the electrochemical HOMO-LUMO
gaps but rather shifts both HOMO/LUMO levels. A similar effect
has been observed for the N-substituent, while type of the
molecules 22 and 24 featuring BA acceptors showed very low
ground state dipole moments, whereas much larger values
were obtained for tripodal molecules 21 and 23 with DCV
acceptors. Except 22, all tripodal molecules possess C3 group of
symmetry.
acceptor and π-system extension reduced the gap significantly.
Multipodal arrangement of CT-chromophores also affects
shape, size, and position of the absorption maxima. Whereas
linear and tripodal molecules showed single CT-bands,
quadrupolar chromophores feature two particularly developed
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bands. A significant red shift has been observed when replacing m/z = 400. The survey crystal positioning systemV(ieswurAvrtieclye OCnPlinSe)
DOI: 10.1039/C6NJ02994A
DCV by BA acceptors and extending/planarizing the π-system. was set for the random choice of shot position by automatic
Type of the auxiliary N-substituent influenced absorption crystal recognition. 2,5-Dihydroxybenzoic acid (DHB) was used
optical properties only negligibly. Nonlinear optical properties as a matrix. Mass spectra were averaged over the whole MS
of
descending order, the measured PO coefficients were affected measured on a Hewlett–Packard 8453 spectrophotometer in
by the acceptor, -system length, branching, and
CH2Cl2at the concentration of 2·10-5 M.
substituents. Performed DFT calculation further confirmed the Thermal properties
1−24 were investigated by photoinduced piezooptics. In the record for all measured samples. The absorption spectra were
π
Ν-
experimental conclusion.
Thermal properties were measured by differential scanning
The main goal of this research work was to shed some light calorimetry DSC with a Mettler-Toledo STARe System DSC 2/700
on basic structural features affecting fundamental properties of equipped with FRS 6 ceramic sensor and cooling system
push-pull chromophores having various arrangements. We HUBERT TC100-MT RC 23. DSC curves were determined in open
believe that the aforementioned findings may serve as a general aluminous crucibles under N2 inert atmosphere and with a
guide for modulating properties of CT-chromophores.
scanning rate of 3 °C/min within the range 25-450 °C. Melting
point and temperature of decomposition were determined as
intersection of baseline and tangent of peak (oneset point).
Electrochemistry
Experimental
Electrochemical
measurements
were
carried
out
in
General
N,N-dimethylformamide containing 0.1 M Bu4NPF6 in a three
Chromophores 136
,
216a
,
318b
,
416a
,
918d,20a,37
,
1720a-b
,
2117b,19a,20a-b electrode cell by cyclic voltammetry (CV), rotating disk
and 2319a are known. For their synthesis and characterization voltammetry (RDV) and polarography. The working electrode was
see to the ESI. The synthesis and characterization of iodo platinum disk (2 mm in diameter) for CV and RDV experiments.
derivatives 28
−
29
,
37
48 and 49
32 36, and 39 are commercially available. auxiliary electrodes. Voltammetric measurements were performed
,
40
−
42 and hydroxy/formyl-substituted Saturated calomel electrode (SCE) separated by a bridge filled
precursors 31
,
43
−
−
54 are given in the ESI. Starting with supporting electrolyte and Pt wire were used as reference and
compounds 27
,
30
,
−
THF was dried in PuresolvTM micro solvent purification system. using a potentiostat PGSTAT 128N (AUTOLAB, Metrohm Autolab
All commercial chemicals and solvents were purchased from B.V., Utrecht, The Netherlands) operated via NOVA 1.10 software.
suppliers such as Sigma Aldrich, Acros and TCI at reagent grade NLO
and were used as obtained. Sonogashira cross-coupling reaction The piezooptical effect was measured for two components of
was carried out in flame-dried flasks under argon. Column the piezooptical tensor: diagonal (
πxxxx) and off-diagonal (πxxzz).
chromatography was carried out with silica gel 60 (particle size They were defined by the directions of the applied mechanical
0.040-0.063 mm, 230-400 mesh; Merck) and commercially stress. The effect for off-diagonal components was at least one
available solvents. Thin-layer chromatography (TLC) was order of magnitude higher. Hence, all the presentation was
conducted on aluminum sheets coated with silica gel 60 F254, given solely for this component. The Senarmont method
obtained from Merck, with visualization by a UV lamp (254 or allowed carrying out the measurements of birefringence with
360 nm). IR spectra were recorded as neat using HATR adapter accuracy up to 10-5. The photo-treatment was performed during
on a Perkin-Elmer FTIR Spectrum BX spectrometer.
probing and immediate after switching off of the monitoring.
NMR
The relaxation of the laser induced changes did not exceed
1H and 13C NMR spectra were recorded at 400/500 and 100/125 several seconds. Additional control of scattering light was done.
MHz, respectively, with a Bruker AVANCE III 400/500 DFT calculations
instruments at 25 °C. Chemical shifts are reported in ppm All calculations were carried out in Gaussian 09W package at the
relative to the signal of Me4Si. The residual solvent signal in the DFT level of theory. Initial geometry optimizations were carried
1H and 13C NMR spectra was used as an internal reference out by PM3 method implemented in program ArgusLab and
(CDCl3 7.25 and 77.23 ppm). Apparent resonance multiplicities subsequently by DFT B3LYP method with 6-311G++(2d,p) basic
are described as s (singlet), d (doublet), dd (doublet of doublet), set. Energies of the HOMO and LUMO (EHOMO and ELUMO), their
and m (multiplet), apparent coupling constants of multiplets (3J differences (∆E) and ground state dipole moments (
or 4J) are given in Hz.
µ
) were
calculated by DFT method B3LYP/6-311++G(2d,p). The first
hyperpolarizabilities were deducted from the optimized
Mass spectroscopy
Mass spectra were measured with a GC-MS configuration geometries using PM7 method implemented in MOPAC2012
comprised of an Agilent Technologies 6890N gas software. See the ESI for more details.
chromatograph equipped with a 5973 Network MS detector (EI General Method for Sonogashira Cross-Coupling (i)
70 eV, mass range 33–550 Da). High resolution MALDI MS Iodo derivative (28 29
, 37,40 42) and propargyl alcohol 38
−
−
spectra were measured on a MALDI mass spectrometer LTQ (1.2/2.4/3.6 eq. for one/two/threefold coupling) were dissolved
Orbitrap XL (Thermo Fisher Scientific, Bremen, Germany) in the solution of THF/Et3N (4:1, 25 mL). Argon was bubbled
equipped with nitrogen UV laser (337 nm, 60 Hz). The LTQ through the solution for 10 min, whereupon [PdCl2(PPh3)2]
Orbitrap instrument was operated in positive-ion mode over a (0.03/0.06/0.09 eq.) and CuI (0.03/0.06/0.09 eq.) were added,
normal mass range (m/z 50-2000) with resolution 100 000 at and the reaction mixture was stirred under argon at 25 °C for 18
10 | J. Name., 2012, 00, 1-3
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hours. The solvents were evaporated in vacuo and the residue 1196, 1103, 790,701 cm-1. HR-MALDI-MS (DHB): calcd for
View Article Online
was taken up in aq. NH4Cl (100 mL) and extracted with of CH2Cl2 C26H31N3O3 (M+) 433.23599 found 433.23D6O5I0:.10.1039/C6NJ02994A
(2×50 mL). The combined organic extracts were dried (Na2SO4) Chromophore 7. The title compound was synthesized from
and the solvents were evaporated in vacuo. The crude product aldehyde 50 (90 mg; 0.383 mmol) and malondinitrile 25 (30 mg;
was purified by column chromatography (SiO2; CH2Cl2 to 0.459 mmol) following the general method (iii). Yield: 66 mg (87
EtOAc/CH2Cl2 1:1).
%); red-violet solid. Rf = 0.9 (SiO2; CH2Cl2); mp 185 °C. Found: C,
General Method for Dess-Martin oxidation (ii)
80.36; H, 4.57; N, 14.79. C19H13N3 requires C, 80.54; H, 4.62; N,
−
Alcohol (43 δ = 3.38 (s, 3H, NCH3),
48) and Dess-Martin reagent (1/2/3 eq. for 14.83 %. 1H NMR (CDCl3, 400 MHz; 25 °C):
one/two/threefold oxidation) were dissolved in CH2Cl2 (20 mL). 6.71 (dd, J1 = 6.8 Hz, J2 = 1.6 Hz, 2H, CHar), 7.09 (s, 1H, CH), 7.21
The reaction mixture was stirred at 25 °C for 4 hours. After (dd, J1 = 8.4 Hz, J2 = 1.2 Hz, 2H, CHar), 7.27 (t, J = 7.2 Hz, 1H,
evaporation of solvent in vacuo the crude product was purified CHar), 7.42 ppm (m, 4H, CHar). 13C NMR (CDCl3, 100 MHz, 25
by column chromatography (SiO2; CH2Cl2).
°C):
126.7, 130.3, 135.5, 141.3, 146.8, 152.1 ppm. FT-IR (HATR):
ν = 3596, 2317, 2154, 1590, 1540, 1369, 1318, 1253, 1180, 991,
δ = 40.5, 88.0, 89.1, 107.7, 112.4, 113.7, 114.2, 120.7, 126.6,
General Method for Knoevenagel condensation (iii)
Aldehydes (30
−
35 and 49
−
54) and malondinitrile 25 or
N,N´-dibutylbarbituric acid 26 (1.2/2.4/3.6 eq. for 824, 708 cm-1. HR-MALDI-MS (DHB): calcd for C19H13N3 (M+)
one/two/threefold condensation) were dissolved in CH2Cl2 283.11040 found 283.11062.
(20 mL) and Al2O3 (5/10/15 eq.; Brockmann activity II-III) was Chromophore 8. The title compound was synthesized from
added. The reaction mixture was stirred at 25 °C for 18 hours. aldehyde 50 (70 mg; 0.297 mmol) and N,N´-dibutylbarbituric
The reaction mixture was filtered and the solvent was acid 26 (86 mg; 0.357 mmol) following the general method (iii).
evaporated in vacuo. The crude product was purified by column Yield: 125 mg (92 %); violet solid. Rf = 0.8 (SiO2; CH2Cl2); mp 119
chromatography (SiO2; CH2Cl2). Chromophores
6
,
10
,
14
,
18
,
°C. Found: C, 73.49; H, 6.97; N, 9.12. C28H31N3O3 requires C,
and 22 with the BA unit(s) directly attached to the phenyl ring(s) 73.50; H, 6.83; N, 9.18 %. 1H NMR (CDCl3, 400 MHz; 25 °C):
δ
=
were partially hydrolyzed to starting compounds during column 0.93 (m, 6H, CH3), 1.35 (m, 4H, CH2), 1.60 (m, 4H, CH2), 3.38 (s,
chromatography and, therefore, they were purified by 3H, NCH3), 3.92 (m, 4H, CH2), 6.73 (m, 2H, CHar), 7.24 (m, 3H,
precipitation from hexane.
Chromophore 5. The title compound was synthesized from CH). 13C NMR (CDCl3, 100 MHz, 25 °C):
CHar), 7.42 (m, 2H, CHar), 7.53 (m, 2H, CHar), 7.80 ppm (s, 1H,
= 13.97, 13.99, 20.36,
δ
aldehyde 31 (150 mg; 0.711 mmol) and malondinitrile 25 (56 20.41, 30.33, 40.5, 41.6, 42.2, 93.3, 110.0, 114.3, 122.4, 124.0,
mg; 0.853 mmol) following the general method (iii). Yield: 66 mg 126.2, 126.5, 130.2, 135.9, 137.2, 147.1, 151.1, 151.8, 159.8,
(94 %); orange solid. Rf = 0.85 (SiO2; CH2Cl2); mp 115 °C. Found: 161.8 ppm. FT-IR (HATR):
ν = 2312, 2156, 1654, 1541, 1400,
C, 77.32; H, 5.51; N, 15.49. C17H13N3 requires C, 78.74; H, 5.05; 1295, 1187, 1047, 978 cm-1. HR-MALDI-MS (DHB): calcd for
1
N, 16.20 %. H NMR (CDCl3, 500 MHz; 25 °C):
δ
= 3.42 (s, 3H, C28H32N3O3 (M+H)+ 458.24382 found 458.24367.
NCH3), 6.72 (d, J = 9.5 Hz, 2H, CHar), 7.22 (dd, J1 = 8.0 Hz, Chromophore 10. The title compound was synthesized from
J2 = 1.0 Hz, 2H, CHar), 7.32 (t, J = 7.5 Hz, 1H, CHar), 7.45 (d, J = aldehyde 32 (213 mg; 0.781 mmol) and N,N´-dibutylbarbituric
7.5 Hz, 2H, CHar), 7.47 (s, 1H, CH), 7.75 ppm (d, J = 9.0 Hz, 2H, acid 26 (234 mg; 0.977 mmol) following the general method (iii).
CHar). 13C NMR (CDCl3, 125 MHz, 25 °C):
115.9, 120.8, 126.9, 127.3, 130.5, 133.7, 146.0, 154.0, 158.3 15 min. After cooling, the precipitate was filtered and this
ppm. FT-IR (HATR): = 2921, 2200, 1607, 1514, 1356, 1173, purification was repeated in order to remove excess of 26. Yield:
1023, 814 cm-1. HR-MALDI-MS (DHB): calcd for C17H13N3 (M+) 317 mg (82 %); red solid. Rf = 0.7 (SiO2; CH2Cl2); mp 108 °C.
259.11040 found 259.11063. Found: C, 75.27; H, 6.87; N, 8.46. C31H33N3O3 requires C, 75.13;
Chromophore 6. The title compound was synthesized from H, 6.71; N, 8.48 %. 1H NMR (CDCl3, 400 MHz; 25 °C):
= 0.93 (m,
δ = 40.6, 113.7, 114.8, The crude product was taken in hexane (10 mL) and refluxed for
ν
δ
aldehyde 31 (150 mg; 0.711 mmol) and N,N´-dibutylbarbituric 6H, CH3), 1.36 (m, 4H, CH2), 1.61 (m, 4H, CH2), 3.94 (m, 4H, CH2),
acid 26 (256 mg; 1.066 mmol) following the general method (iii). 6.92 (d, J = 8.8 Hz, 2H, CHar), 7.18 (m, 6H, CHar), 7.33 (m, 4H,
The crude product was taken in hexane (10 mL) and refluxed for CHar), 8.20 (d, J = 9.2 Hz, 2H, CHar), 8.40 ppm (s, 1H, CH). 13C
15 min. After cooling, the precipitate was filtered and this NMR (CDCl3, 100 MHz, 25 °C):
purification was repeated in order to remove excess of 26. Yield: 42.3, 112.8, 118.0, 124.8, 125.8, 126.8, 129.9, 138.0, 145.6,
190 mg (62 %); orange solid. Rf = 0.65 (SiO2; CH2Cl2); mp 142 °C. 151.2, 153.0, 158.2, 161.1, 163.3 ppm. FT-IR (HATR): = 2930,
Found: C, 72.09; H, 7.21; N, 9.69. C26H31N3O3 requires C, 72.03; 2314, 1648, 1488, 1406, 1295, 1195, 1105, 993, 757, 698 cm-1.
H, 7.21; N, 9.69 %. 1H NMR (CDCl3, 500 MHz; 25 °C): = 0.94 (m, HR-MALDI-MS (DHB): calcd for C31H34N3O3 (M+H)+ 496.25947
δ = 14.0, 20.32, 20.36, 30.3, 41.7,
ν
δ
6H, CH3), 1.37 (m, 4H, CH2), 1.59 (m, 4H, CH2), 3.43 (s, 3H, NCH3), found 496.25725.
3.94 (m, 4H, CH2), 6.73 (d, J = 9.0 Hz, 2H, CHar), 7.23 (dd, Chromophore 11. The title compound was synthesized from
J1 = 7 Hz, J2 = 1.0 Hz, 2H, CHar), 7.29 (t, J = 7.0 Hz, 1H, CHar), aldehyde 51 (84 mg; 0.282 mmol) and malondinitrile 25 (22 mg;
7.43 (m, 2H, CHar), 8.28 (d, 2H, J = 9 Hz, CHar), 8.41 ppm (s, 1H, 0.339 mmol) following the general method (iii). Yield: 70 mg (72
CH). 13C NMR (CDCl3, 125 MHz, 25 °C):
20.47, 30.42, 30.43, 40.6, 41.8, 42.4, 111.3, 113.1, 122.6, 126.9, H, 4.30; N, 11.72. C24H15N3 requires C, 83.46; H, 4.38; N, 12.17
127.0, 130.3, 138.9, 146.3, 151.4, 153.8, 158.8, 161.4, 163.8 %. 1H NMR (CDCl3, 500 MHz; 25 °C):
= 6.93 (d, J = 9.0 Hz, 2H,
ppm. FT-IR (HATR): = 2929, 1652, 1508, 1407, 1360, 1303, CHar), 7.10 (s, 1H, CH), 7.16 (m, 6H, CHar), 7.33 (m, 4H, CHar),
δ = 14.03, 14.05, 20.42, %); red solid. Rf = 0.9 (SiO2; CH2Cl2); mp 178 °C. Found: C, 81.95;
δ
ν
7.39 ppm (d, J = 9 Hz, 2H, CHar). 13C NMR (CDCl3, 125 MHz, 25
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 11
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ARTICLE
Journal Name
°C):
130.0, 135.1, 141.3, 146.0, 151.6 ppm. FT-IR (HATR):
1586, 1540, 1340, 1177, 996, 826, 692 cm-1. HR-MALDI-MS 383.11655 found 383.11664.
δ
= 87.3, 90.5, 110.7, 112.2, 113.4, 119.0, 125.5, 126.5, IR (HATR):
ν = 2308, 2161, 1589, 1537, 1333, 126V3i,ew1A1r0tic4le, O9n9li9ne,
ν
= 2146, 819 cm-1. HR-MALDI-MS (DHB): calcdDOfIo: 1r0.1C03259H/C163NNJ502(9M94+A)
(DHB): calcd for C24H15N3 (M+) 345.12605 found 345.12619.
Chromophore 16. The title compound was synthesized from
Chromophore 12. The title compound was synthesized from aldehyde 52 (200 mg; 0.697 mmol) and N,N´-dibutylbarbituric
aldehyde 51 (64 mg; 0.215 mmol) and N,N´-dibutylbarbituric acid 26 (401 mg; 1.672 mmol) following the general method (iii).
acid 26 (62 mg; 0.258 mmol) following the general method (iii). Yield: 460 mg (90 %); violet solid. Rf = 0.4 (SiO2; CH2Cl2). Found:
Yield: 80 mg (71 %); dark violet solid. Rf = 0.65 (SiO2; CH2Cl2); mp C, 70.40; H, 6.80; N, 9.75. C43H49N5O6 requires C, 70.57; H, 6.75;
1
126 °C. Found: C, 76.02; H, 6.45; N, 8.15. C33H33N3O3 requires C, N, 9.57 %. H NMR (CDCl3, 500 MHz; 25 °C):
76.28; H, 6.40; N, 8.09 %. 1H NMR (CDCl3, 400 MHz; 25 °C):
δ = 0.94 (m, 12H,
CH3), 1.37 (m, 8H, CH2), 1.61 (m, 8H, CH2), 3.44 (s, 3H, NCH3),
δ
=
0.94 (m, 6H, CH3), 1.37 (m, 4H, CH2), 1.61 (m, 4H, CH2), 3.93 (m, 3.93 (m, 8H, CH2), 7.09 (d, J = 9.0 Hz, 4H, CHar), 7.63 (d, J = 8.5
4H, CH2), 6.95 (d, J = 8.8 Hz, 2H, CHar), 7.14 (m, 6H, CHar), 7.31 Hz, 4H, CHar), 7.79 ppm (s, 2H, CH). 13C NMR (CDCl3, 125 MHz,
(m, 4H, CHar), 7.51 (d, J = 9.2 Hz, 2H, CHar), 7.78 ppm (s, 1H, 25 °C):
CH). 13C NMR (CDCl3, 100 MHz, 25 °C):
= 14.0, 20.36, 20.39, 91.8, 115.0, 119.9, 120.6, 124.2, 135.5, 136.7, 150.0, 150.9,
30.3, 41.7, 42.2, 92.3, 113.2, 120.3, 121.7, 123.5, 125.1, 126.3, 159.6, 161.4 ppm. FT-IR (HATR): = 2150, 1663, 1543, 1397,
29.9, 135.4, 136.9, 146.4, 151.02, 151.08, 159.6, 161.6 ppm. FT- 1339, 1294, 1181, 1047, 976, 756 cm-1. HR-MALDI-MS (DHB):
IR (HATR):
= 2322, 2164, 1654, 1559, 1400, 1268, 1165, 1050, calcd for C43H50N5O6 (M+H)+ 732.37557 found 732.37580.
981, 756, 694 cm-1. HR-MALDI-MS (DHB): calcd for C33H34N3O3 Chromophore 18. The title compound was synthesized from
(M+H)+ 520.25947 found 520.25880.
aldehyde 34 (301 mg; 1 mmol) and N,N´-dibutylbarbituric acid
δ = 13.97, 13.99, 20.35, 20.39, 30.3, 40.2, 41.8, 42.3,
δ
ν
ν
Chromophore 13. The title compound was synthesized from 26 (864 mg; 3.6 mmol). Both reaction components were
aldehyde 33 (150 mg; 0.628 mmol) and malondinitrile 25 dissolved in CH3CN (15 mL), Al2O3 (1.02 g; 10.0 mmol) were
(99 mg; 1.507 mmol) following the general method (iii). Yield: added and the reaction mixture was stirred at 60 °C for 18 h.
160 mg (76 %); orange solid. Rf = 0.65 (SiO2; CH2Cl2); mp 206 °C. After cooling, the solution was filtered and the solvent was
Found: C, 73.93; H, 3.85; N, 20.31. C21H13N5 requires C, 75.21; H, evaporated in vacuo. The crude product was taken in hexane
1
3.91; N, 20.88 %. H NMR (CDCl3, 400 MHz; 25 °C):
δ = 3.53 (s, (10 mL) and refluxed for 15 min. After cooling, the precipitate
3H, NCH3), 7.20 (d, J = 9.2 Hz, 4H, CHar), 7.63 (s, 2H, CH), 7.89 was filtered and this purification was repeated in order to
ppm (d, J = 9.2 Hz, 4H, CHar). 13C NMR (CDCl3, 100 MHz, 25 °C): remove excess of 26. Yield: 550 mg (74 %); red solid. Rf = 0.4
δ
= 40.3, 113.5, 114.6, 121.0, 125.6, 133.1, 151.9, 158.1 ppm. (SiO2; CH2Cl2). Found: C, 70.66; H, 6.87; N, 9.54. C44H51N5O6
FT-IR (HATR):
= 2215, 1571, 1504, 1358, 1195, 828, 817 cm-1. requires C, 70.85; H, 6.89; N, 9.39 %. 1H NMR (CDCl3, 400 MHz;
HR-MALDI-MS (DHB): calcd for C21H13N5 (M+) 335.11655 found 25 °C):
= 0.93 (m, 12H, CH3), 1.36 (m, 8H, CH2), 1.61 (m, 8H,
335.11671. CH2), 3.95 (m, 8H, CH2), 7.13 (d, J = 8.8 Hz, 4H, CHar), 7.20 (d,
ν
δ
Chromophore 14. The title compound was synthesized from J = 7.2 Hz, 2H, CHar), 7.28 (m, 1H, CHar), 7.36 (m, 2H, CHar), 8.18
aldehyde 33 (150 mg; 0.628 mmol) and N,N´-dibutylbarbituric (d, J = 8.8 Hz, 4H, CHar), 8.43 ppm (s, 2H, CH). 13C NMR (CDCl3,
acid 26 (362 mg; 1.507 mmol) following the general method (iii). 100 MHz, 25 °C):
The crude product was taken in hexane (10 mL) and refluxed for 122.1, 127.0, 127.6, 127.8, 130.4, 137.1, 145.0, 150.9, 151.1,
15 min. After cooling, the precipitate was filtered and this 157.8, 160.9, 163.0 ppm. FT-IR (HATR): = 2956, 2361, 1663,
δ = 14.0, 20.38, 20.41, 30.4, 41.9, 42.6, 115.3,
ν
purification was repeated in order to remove excess of 26. Yield: 1552, 1499, 1403, 1329, 1294, 1187, 1102, 993, 791 cm-1. HR-
200 mg (47 %); terracotta solid. Rf = 0.3 (SiO2; CH2Cl2); mp 134 MALDI-MS (DHB): calcd for C44H52N5O6 (M+H)+ 746.39121 found
°C. Found: C, 68.32; H, 7.24; N, 10.25. C39H49N5O6 requires C, 746.38932.
68.50; H, 7.22; N, 10.24 %. 1H NMR (CDCl3, 400 MHz; 25 °C):
δ
=
Chromophore 19. The title compound was synthesized from
0.95 (m, 12H, CH3), 1.40 (m, 8H, CH2), 1.64 (m, 8H, CH2), 3.52 (s, aldehyde 53 (100 mg; 0.286 mmol) and malondinitrile 25
3H, NCH3), 3.96 (m, 8H, CH2), 7.17 (d, J = 8.8 Hz, 4H, CHar), 8.24 (45 mg; 0.687 mmol) following the general method (iii). Yield:
(d, J = 9.2 Hz, 4H, CHar), 8.46 ppm (s, 2H, CH). 13C NMR (CDCl3, 100 mg (78 %); violet solid. Rf = 0.75 (SiO2; CH2Cl2); mp 195 °C.
100 MHz, 25 °C):
42.5, 115.0, 119.9, 127.1, 137.3, 151.1, 151.4, 158.0, 160.9, 3.39; N, 15.72 %. 1H NMR (CDCl3, 400 MHz; 25 °C):
163.0 ppm. FT-IR (HATR): = 2856, 2367, 1650, 1499, 1405, = 8.8 Hz, 4H, CHar), 7.12 (s, 2H, CH), 7.14 (d, J = 7.6 Hz, 2H, CHar),
1349, 1299, 1187, 1101, 975, 791 cm-1. HR-MALDI-MS (DHB): 7.25 (m, 1H, CHar), 7.39 (m, 2H, CHar), 7.48 ppm (d, J = 8.8 Hz,
calcd for C39H50N5O6 (M+H)+ 684.37556 found 684.35420. 4H, CHar). 13C NMR (CDCl3, 125 MHz, 25 °C):
= 86.7, 92.3,
Chromophore 15. The title compound was synthesized from 111.9, 113.0, 113.9, 116.6, 123.1, 126.7, 127.1, 130.4, 135.1,
aldehyde 52 (100 mg; 0.348 mmol) and malondinitrile 25 141.2, 145.2, 149.9 ppm. FT-IR (HATR): = 2319, 2166, 1591,
δ
= 13.99, 14.01, 20.38, 20.43, 30.4, 40.2, 41.9, Found: C, 80.69; H, 3.40; N, 15.61. C30H15N5 requires C, 80.88; H,
δ
= 7.08 (d, J
ν
δ
ν
(55 mg; 0.835 mmol) following the general method (iii). Yield: 1541, 1488, 1321, 1265, 1170, 1022, 830, 640 cm-1. HR-MALDI-
100 mg (75 %); violet solid. Rf = 0.7 (SiO2; CH2Cl2); mp 182 °C. MS (DHB): calcd for C30H15N5 (M+) 445.13220 found 445.13268.
Found: C, 77.10; H, 3.46; N, 17.39. C25H13N5 requires C, 78.32; H, Chromophore 20. The title compound was synthesized from
1
3.42; N, 18.27 %. H NMR (CDCl3, 400 MHz; 25 °C):
δ = 3.45 (s, aldehyde 53 (80 mg; 0.228 mmol) and N,N´-dibutylbarbituric
3H, NCH3), 7.11 (m, 6H, CHar+CH), 7.54 ppm (d, J = 8.8 Hz, 4H, acid 26 (131 mg; 0.547 mmol) following the general method (iii).
CHar). 13C NMR (CDCl3, 100 MHz, 25 °C):
= 40.2, 86.8, 92.0, Yield: 130 mg (72 %); dark red solid. Rf = 0.6 (SiO2;
111.9, 113.0, 113.1, 116.9, 120.8, 135.2, 141.2, 150.3 ppm. FT- CH2Cl2/acetone 50:1). Found: C, 72.40; H, 6.56; N, 9.01.
δ
12 | J. Name., 2012, 00, 1-3
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ARTICLE
C48H51N5O6 requires C, 72.61; H, 6.47; N, 8.82 %. 1H NMR (CDCl3,
400 MHz; 25 °C): = 0.94 (m, 12H, CH3), 1.36 (m, 8H, CH2), 1.61
2008, 108, 1245; d) Y. Ohmori, Laser Photonics VRieewv.A,rt2ic0le1O0n,line
4,
300.
DOI: 10.1039/C6NJ02994A
δ
2
3
4
5
A. Abbotto, L. Beverina, R. Bozio, S. Bradamante, C. Ferrante,
G. A. Pagani and R. Signorini, Adv. Mater., 2000, 12, 1963.
M. Qin, C. Wang, F. Zhao, P. Zeng, P. Cai, M. Fang and G. Lu,
Opt. Eng., 2015, 54, 057101.
L. M. Ganesan, W. Wirges, A. Mellinger and R. Gerhard, J.
Phys. D: Appl. Phys., 2010, 43, 015401.
a) M. Pawlicki, H. A. Collins, R. G. Denning and H. L. Anderson,
Angew. Chem. Int. Ed., 2009, 48, 3244; b) F. Terenziani, C.
Katan, E. Badaeva, S. Tretiak and M. Blanchard-Desce, Adv.
Mater., 2008, 20, 4641.
A. W. Hains, Z. Liang, M. A. Woodhouse and B. A. Gregg, Chem.
Rev., 2010, 110, 6689.
a) Y. Wu and W. Zhu, Chem. Soc. Rev., 2013, 42, 2039; b) J. N.
Clifford, E. Martínez-Ferrero, A. Viterisi and E. Palomares,
Chem. Soc. Rev., 2011, 40, 1635; c) C. Duan,K. Zhang, C. Zhong,
F. Huang and Y. Cao, Chem. Soc. Rev., 2013, 42, 9071; d) M.
Liang and J. Chen, Chem. Soc. Rev., 2013, 42, 3453.
(m, 8H, CH2), 3.93 (m, 8H, CH2), 7.07 (d, J = 8.4 Hz, 4H, CHar),
7.14 (d, J = 8.4 Hz, 2H, CHar), 7.23 (m, 1H, CHar), 7.36 (m, 2H,
CHar), 7.57 (d, J = 8.4 Hz, 4H, CHar), 7.77 ppm (s, 2H, CH). 13C
NMR (CDCl3, 100 MHz, 25 °C): δ = 14.0, 20.35, 20.39, 30.3, 41.8,
42.3, 91.6, 115.9, 119.2, 123.1, 124.6, 126.2, 126.9, 130.2,
135.3, 136.5, 145.6, 149.5, 150.9, 159.5, 161.4 ppm. FT-IR
(HATR):
ν = 2324, 2161, 1662, 1549, 1397, 1268, 1174, 1049,
997, 787 cm-1. HR-MALDI-MS (DHB): calcd for C48H52N5O6
(M+H)+ 794.39121 found 794.39186.
6
7
Chromophore 22. The title compound was synthesized from
aldehyde 35 (100 mg; 0.304 mmol) and N,N´-dibutylbarbituric
acid 26 (263 mg; 1.094 mmol). Both reaction components were
dissolved in CH3CN (15 mL), Al2O3 (460 mg; 4.5 mmol) were
added and the reaction mixture was stirred at 60 °C for 18 h.
After cooling, the solution was filtered and the solvent was
evaporated in vacuo. The crude product was taken in hexane
(10 mL) and refluxed for 15 min. After cooling, the precipitate
was filtered and this purification was repeated in order to
remove excess of 26. Yield: 190 mg (64 %); violet solid. Rf = 0.5
(SiO2; CH2Cl2/acetone 50:1). Found: C, 68.44; H, 6.93; N, 9.68.
C57H69N7O9 requires C, 68.72; H, 6.98; N, 9.84 %. 1H NMR (CDCl3,
8
9
C. Duan, F. Huang and Y. Cao, J. Mater. Chem., 2012, 22
10416.
P. Batail, Chem. Rev., 2004, 104, 4887.
,
10 S. Allard, M. Forster, B. Souharce, H. Thiem and U. Scherf,
Angew. Chem. Int. Ed., 2008, 47, 4070.
11 a) J. Kulhánek, F. Bureš, J. Opršal, W. Kuznik, T. Mikysek and A.
Růžička, Asian J. Org. Chem., 2013, 2, 422; b) P. D. Jarowski
and Y. Mo, Chem. Eur. J., 2014, 20, 17214; c) H. Meier, Angew.
Chem. Int. Ed., 2005, 44, 2482; d) J. Y. Lee, K. S. Kim and B. J.
Mhin, J. Chem. Phys., 2001, 115, 9484; e) F. Bureš, O. Pytela,
M. Kivala and F. Diederich, J. Phys. Org. Chem., 2011, 24, 274.
12 T. Kolev, B. Koleva, J. Kasperczyk, I. Kityk, S. Tkaczyk, M.
Spiteler, A. H. Reshak and W. Kuznik, J. Mater. Sci.: Mater.
Electron., 2009, 20, 1073.
500 MHz; 25 °C): δ = 0.95 (m, 18H, CH3), 1.38 (m, 12H, CH2), 1.63
(m, 12H, CH2), 3.96 (m, 12H, CH2), 7.21 (d, J = 9.0 Hz, 6H, CHar),
7.18 (d, J = 8.5 Hz, 6H, CHar), 8.46 ppm (s, 3H, CH). 13C NMR
(CDCl3, 125 MHz, 25 °C):
116.4, 124.0, 129.2, 136.7, 149.8, 151.0, 157.5, 160.7, 162.7
ppm. FT-IR (HATR): = 3332, 2932, 2304, 1660, 1495, 1402,
δ = 14.0, 20.38, 20.41, 30.3, 42.0, 42.6,
13 a) S. R. Marder and J. W. Perry, Adv. Mater., 1993,
D. R. Kanis, M. A. Ratner and T. J. Marks, Chem. Rev., 1994, 94
5, 804; b)
,
ν
1323, 1269, 1181, 1102, 791, 758 cm-1. HR-MALDI-MS (DHB):
calcd for C57H70N7O9 (M+H)+ 996.52295 found 996.52909.
Chromophore 24. The title compound was synthesized from
aldehyde 54 (30 mg; 0.075 mmol) and N,N´-dibutylbarbituric
acid 26 (65 mg; 0.269 mmol) following the general method (iii).
Yield: 52 mg (65 %); violet solid. Rf = 0.55 (SiO2; CH2Cl2/acetone
50:1). Found: C, 70.69; H, 6.67; N, 9.22. C63H69N7O9 requires C,
70.83; H, 6.51; N, 9.18 %. 1H NMR (CDCl3, 400 MHz; 25 °C):
195; c) L. R. Dalton, J. Phys.: Condens. Matter, 2003, 15, R897;
d) M. G. Kuzyk, J. Mater.Chem., 2009, 19, 7444.
14 F. Bureš, RSC Adv., 2014, 4, 58826.
15 a) E. Genin, V. Hugues, G. Clermont, C. Herbivo, M. C. R.
Castro, A. Comel, M. M. M. Raposo and M. Blanchard-Desce,
Photochem. Photobiol. Sci., 2012, 11, 1756; b) C. Herbivo, A.
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δ
= 0.94 (m, 18H, CH3), 1.36 (m, 12H, CH2), 1.61 (m, 12H, CH2),
3.93 (m, 12H, CH2), 7.12 (d, J = 8.4 Hz, 6H, CHar), 7.62 (d,
J = 8.8 Hz, 6H, CHar), 7.77 ppm (s, 3H, CH). 13C NMR (CDCl3,
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,
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100 MHz, 25 °C):
91.4, 117.6, 117.8, 124.5, 125.2, 135.4, 136.2, 148.5, 150.8,
159.4, 161.3 ppm. FT-IR (HATR): = 3321, 2332, 2165, 1662,
1558, 1398, 1317, 1268, 1174, 1052, 971 cm-1. HR-MALDI-MS
(DHB): calcd for C63H70N7O9 (M+H)+1068.52295 found
1068.52129.
δ = 13.95, 13.97, 20.34, 20.38, 30.3, 41.8, 42.3,
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Acknowledgements
This research was supported the Technology Agency of the
Czech Republic (TE01020022, Flexprint).
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DOI: 10.1039/C6NJ02994A
Branching along with the acceptor nature and π-system length were revealed
as crucial factors affecting the fundamental optoelectronic properties of
push-pull molecules.
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