N,N′-Dibutylbarbituric acid as an acceptor moiety in push-pull chromophores

Article abstract of DOI:10.1039/c3nj00683b

Twelve novel D-π-A chromophores with the N,N′-dibutylbarbituric acid acceptor, the N,N-dimethylamino donor and a systematically extended π-linker were synthesized. The extent of intramolecular charge-transfer, structure-property relationships and nonlinear optical properties were further investigated by X-ray analysis, electrochemistry, UV/Vis absorption spectra, calculations and EFISH experiments.

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New Journal of Chemistry
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DOI: 10.1039/C3NJ00683B
Table of Contents Entry
Organic push-pull molecules with N,N’-dibutylbarbituric acid acceptor and N,N-dimethylamino donor
have been synthesized and further investigated as charge-transfer chromophores for nonlinear
optics.

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N,N’-Dibutylbarbituric acid as an acceptor moiety in push-pull
chromophores
Milan Klikar,a Filip Bureš,*,a Oldřich Pytela,a Tomáš Mikysek,b Zdeňka Padělková,c Alberto Barsella,d
Kokou Dorkenood and Sylvain Achellee
5
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
Twelve novel D--A chromophores with N,N’-dibutylbarbituric acid acceptor, N,N-dimethylamino donor and systematically extended
-linker were synthesized. The extent of intramolecular charge-transfer, structure-property relationships and nonlinear optical properties
were further investigated by X-ray analysis, electrochemistry, UV/Vis absorption spectra, calculations and EFISH experiment.
10
distinct solvatochromism and were investigated as powerful
probes i) to study solvent effects, solvent/medium polarity and
pH-sensitivity; ii) to distinguish between the specific and non-
Introduction
Design, synthesis and application of novel -conjugated
50 specific solvent interactions and iii) to assess hydrogen bonding
molecules in materials science have been subject of considerable
ability.8 The latter property of hydrogen-bonding was further
research interest.1 In a -conjugated molecule equipped with an
utilized in supramolecular assemblies of (T)BA derivatives
15 electron-donor (D) and an electron-acceptor (A), so-called D--A
or push-pull chromophore, intramolecular charge-transfer (ICT)
from the donor to the acceptor occurs. The ICT can easily be
illustrated by two limiting resonance forms (aromatic and
quinoid/zwitterionic arrangement).2 The D-A interaction and
20 simultaneous generation of a new low-energy molecular orbital
determines the unique properties of push-pull chromophores such
as intensive colour, dipolar character, electrochemical behaviour,
crystallinity, intermolecular interactions (-stacking) as well as
nonlinear optical (NLO) properties. Within the last 30 years or so,
25 it has been realized that prepolarization of an organic molecule in
D--A arrangement significantly enhances its NLO response.
Hence, various -conjugated backbones and electron donating
and withdrawing groups and moieties were utilized in the
construction of NLO-active molecules (NLOphores) up to date.3
30 Since the first synthesis by Adolf von Baeyer in 1864, barbituric
acid (BA) and its derivatives found widespread applications
across many branches.4 The uses of C5-(di)alkylated BAs
(barbitals) as hypnotic-sedative agents, anticonvulsant,
antimicrobial, spasmolytic, antiinflammatory, antitumoral and
35 fat-reducing agents are apparently the most widely known
pharmacological applications.5 Beside this, BA-derived anionic
dyes (Oxonols, DiSBACs) may act as fast voltage FRET probes
monitoring changes of the cell membrane potential.6
exhibiting photoelectrochemical, photorefractive, semiconducting
and distinct absorption and fluorescent properties.9 Yagai et al.
55 showed several impressive hydrogen-bonded nanorings,
nanofibres and rosettes,10 while Bassani et al. demonstrated
application of such hierarchical self-assemblies in organic
photovoltaic devices.11
Push-pull chromophores featuring (T)BA acceptor unit were
60 also widely studied as efficient NLOphores. Hence, C5
methylidene substituted (T)BA push-pull derivatives proved to be
highly prepolarized and showed high nonlinear optical
coefficients  up to 300×10-30 esu.12 Considering the number of
(T)BA push-pull chromophores synthesized to date, it is
65 somewhat curious that only few efforts were made to
systematically study the influence of the structure and length of
the -linker connecting (T)BA acceptor and a given donor.13
Hence, in this work we have focused on push-pull chromophores
1-3 with the -conjugated system consisting of multiple bonds
70 and
1,4-phenylene
moieties
end-capped
with
N,N’-dibutylbarbituric acid and N,N-dimethylamino group
(Fig. 1). These groups have been chosen as electron acceptor and
donor, while the butyl substituents assure chromophore sufficient
solubility and simultaneously retain the possibility of its
75 crystallization and study by X-ray analysis.
However, pseudoaromatic pyrimidine-2,4,6-trione ring in BA can
40 also be employed as electron-withdrawing moiety in push-pull
chromophores. This class of BA-derived compounds can be
represented by merocyanine dyes, especially by the well-known
merocyanine 540.7 Up to date, (thio)barbituric acid ((T)BA) and
their push-pull derivatives found admirable number of
45 applications, especially in materials sciences. Either N-alkylated
or N-unsubstituted (T)BA derivatives showed very strong and
Bu
O
N
O
N
O
Bu
D- -A
-linker
1-3
N
Fig. 1 General structure of target push-pull chromophores 1-3
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According to the N,N’-dibutylbarbituric acid connection to the 20 cinnamaldehydes and propargyl aldehydes required for the final
central -linker, three series of compounds 1-3 were synthesized.
Each series contains four compounds a-d that differ in the length
and structures of the -linker (a – 1,4-phenylene, b – 4,4’-
Knoevenagel condensation were prepared in a modular manner as
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shown in Scheme 1. 1,4-Diiodobenzene 4 was used as suitable
DOI: 10.1039/C3NJ00683B
starting compound. Its formylation afforded 4-iodobenzaldehyde
5
biphenylene,
c
–
(E)-phenylethenylphenyl
and
6 in 44% yield. Transformation into (E)-4-iodocinnamaldehyde 7
d – phenylethynylphenyl). These model push-pull chromophores 25 was accomplished via Wittig reaction of
6
with
were further investigated by X-ray analysis, electrochemistry,
UV/Vis spectra, calculations and EFISH experiment to evaluate
the extent of the ICT and fundamental structure-property
(triphenylphosphoranylidene)acetaldehyde
and
subsequent
isomerization in the overall yield of 59%. Sonogashira cross-
coupling on 4 and 4-iodo-N,N-dimethylaniline 7 with propargyl
alcohol afforded alcohols 8 (51%) and 9 (67%).17 Their oxidation
30 with Dess-Martin periodinane provided extended propargyl
aldehydes 10 and 11 in the yields of 94 and 76 %, respectively.18
The -systems of iodo-substituted aldehydes 6, 7 and 10 were
further extended by Suzuki-Miyaura (Method A), Heck (Method
B) and Sonogashira (Method C) reactions with boronic acid
of 35 pinacol ester 12, styrene 13 and terminal acetylene 14,
respectively. These reactions yielded biphenyl aldehydes 15-17,
stilbene aldehydes 18-20 and phenylethynylphenyl aldehydes
21-23 in the indicated yields. For the synthetic details and the
characterization of aldehydes 15-23 see the Electronic
10 relationships.
Results and Discussion
Synthesis
The obvious retrosynthetic strategy leading to target
chromophores
1-3
involves
the
synthesis
15 N,N’-dibutylbarbituric acid and its Knoevenagel reaction14 with
extended aldehydes. The barbituric acid was synthesized from
N,N’-dibutylurea, generated from butyl isocyanate and
butylamine in 99% yield15 and its subsequent treatment with
malonic acid (91
%
yield).16 Extended benzaldehydes, 40 Supplementary Information (ESI).
HO
O
O
I
CHO
1. nBuLi/THF/-78 °C
2. DMF
OH
Dess-Martin
periodinane
1. Ph3P=CH-CHO
2. I2/toluene/
3. KH2PO4 (aq.)
Method C
R
I
I
R
R
10 R = I
11 R = NMe2
8 R = I
9 R = NMe2
7
4 R = I
5 R = NMe2
6
B(pin)
CHO
N
CHO
N
N
N
O
15 (90 %)
18 (92 %)
O
N
N
12
Method A
13
6, 7 or 10
N
N
Method B
16 (94 %)
17 (72 %)
19 (92 %)
20 (64 %)
O
O
Method C
N
14
N
N
N
CHO
21 (82 %)
22 (94 %)
23 (62 %)
O
O
Scheme 1 Synthetic approach to extended aldehydes 15-23
2
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Despite the recent progress in the catalytic
Knoevenagel condensation,19 we have adopted in our strategy
very mild and efficient methodology of Al2O3-catalyzed
reaction developed by Foucaud20 and further applied by
Diederich et al. for the construction of dicyanovinyl acceptor
moiety in cyanoethynylethenes (CEEs).21 This methodology
proved to be also very useful for the condensation of aldehydes
and N,N’-dibutylbarbituric acid. Commercially available
4-N,N-dimethylamino-substituted benzaldehyde 24 and
cinnamaldehyde 25 as well as extended aldehydes 11 and 15-
23 were converted into target push-pull chromophores 1a-d,
2a-d and 3a-d in the yields of 49–81, 76–91 and 69–82 %
(Scheme 2). Whereas the products of Knoevenagel reaction 1a,
2a-d and 3a-d could be purified by simple column
chromatography, chromophores 1b-d decomposed already
during the TLC analysis. It has recently been shown that the
exocyclic double bond in BA benzylidene derivatives
possesses highly electrophilic character and undergoes facile
15
20
25
5
reaction with various nucleophiles.22 Hence,
a
retro
Knoevenagel reaction with traces of water or acid media most
likely takes place during the purification of 1b-d on silica.
Therefore, the equilibrium condensation of extended
benzaldehydes 15, 18 and 21 was carried out with
2 equivalents of N,N’-dibutylbarbituric acid and products 1b-d
were purified by repeated precipitation from hot hexane.
10
Series
1
Bu
O
N
O
Bu
O
N
O
N
N
O
Bu
O
Bu
N
N
Bu
O
(49 %)
1b
1d
(81 %)
1a
N
Bu
O
N
O
O
N
O
Bu
N
O
Bu
N
N
(77 %)
1c
(75 %)
Bu
O
Bu
O
N
O
Series
2
N
N
O
N
O
Bu
O
Bu
O
or
11 15-23
Bu
O
Bu
O
N
N
N
N
O
N
N
CHO
(85 %)
2a
Bu
(91 %)
2b
N
Bu
O
N
O
O
24
25
Al2O3/Na2SO4
CH2Cl2
O
N
O
Bu
N
O
Bu
N
N
(80 %)
O
(76 %)
2d
2c
3a
Bu
O
N
Bu
O
Series
3
N
N
O
Bu
N
O
Bu
N
O
N
Bu
O
N
O
N
Bu
O
N
O
(77 %)
(81 %)
(69 %)
3b
3d
O
Bu
N
O
Bu
N
N
(82 %)
3c
Scheme 2 Knoevenagel condensation and structures of target chromophores 1-3
Having difficulties with the synthesis of 1b-d, we have attempted 30 substituted aldehydes 6, 7 and 10 yielding intermediates 26-28
an alternative synthetic route as shown in Scheme S1 (see the
ESI). This strategy involves Knoevenagel condensation of iodo-
and their subsequent modification via cross-coupling reactions
(Methods A-C). However, these procedures led only to isolation
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New Journal of Chemistry
of chromophores 2a-b in the yields of 25–70 %. The
C8-C9) for 1a and 2b, respectively. Such planar arrangement of
cross-coupling reactions on 26 provided intensively coloured
solutions, in which target compounds 1b-d were detected by TLC
the -systems in 1a and 2a would allow efficient D-A interaction.
The extent of the ICT and molecule polarDizOaIt:io1n0.1c0a3n9/eCa3sNilJy00b6e83B
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and HR-MALDI-MS. Nevertheless, isolation of pure 25 assessed by evaluating quinoid character r and bond length
5
chromophores was not possible. On the other hand, cross-
coupling reactions on 28 provided directly a mixture of several
alternation of the -system used. Average quinoid character of
the 1,4-phenylene moieties in 1a and 2a are 0.05 and 0.04,
respectively. For benzene, r = 0, while in fully quinoid rings is
r equal to 0.08–0.1. Hence, the measured values indicate a
products of degradation. Most probably,
a
conjugated
nucleophilic addition on electrophilic triple bond in 28 takes
place under the conditions of cross-coupling reactions and caused 30 considerable -system polarization and rival those measured for
10 degradation.21d
highly polarized CEEs, which exhibited r within the range of
0.03–0.07.21 Quinoid characters of the propen-1,3-diyl (C3-C5-
C6) and pent-1,3-dien-1,5-diyl (C3-C5-C6-C7-C8) -linker
segments in 1a and 2a are 0.04 and 0.06. Fig. S1 and S2 in the
35 ESI show the crystal packing of 1a and 2a. In the solid state,
chromophore 1a doesn’t adopt a D to A molecular arrangement
typical for the crystallization of dipolar compounds. This is most
likely due to the less extended -system and significant influence
of the butyl residues (interlayer distance of about 3.6 Å). On the
40 contrary, the crystal packing of chromophore 2a shows typical D
to A intermolecular interactions and -stacks with the interlayer
distance less than 3.4 Å.
X-ray analysis
All target compounds 1-3 are thermally stable and intensely
coloured solids readily soluble in chlorinated solvents. Target
push-pull chromophores 1a and 2a were crystalized by slow
15 diffusion of hexane into their solutions in dichloromethane. Fig. 2
shows the ORTEP plots and confirms the molecular structures
assigned to 1a and 2a. Both front and side views are provided. As
can be seen, both butyl residues stick oppositely and almost
perpendicularly to the -system mean plain. Average torsion
20 angles between the barbituric acid ring and the adjacent
1,4-phenylene moieties are 4.5° (C2-C3-C6-C7) and 0.4° (C2-C3-
Fig. 2 ORTEP representations of chromophore 1a (a) and 2a (b) measured by X-ray analysis at 150 K (50% probability level)
first reduction involved the barbituric acid acceptor moiety and
the adjacent part of the -linker. The half-wave potentials E1/2 of
Electrochemistry
45 Electrochemical behaviour of chromophores 1-3 was investigated
by cyclic voltammetry (CV) and rotating-disc voltammetry
(RDV). The measurements were carried out in acetonitrile that
contained 0.1 M Bu4NPF6 as the electrolyte in a three-electrode
cell. A saturated calomel electrode (SCE) separated by a bridge
50 filled with supporting electrolyte and Pt wire were used as the
reference and auxiliary electrodes, respectively. The acquired
data are summarized in Table 1. Table S1 and Fig. S3–S6 in the
ESI contain full electrochemical data and representative CV
curves for compounds 1a, 2b, 2c and 3d. Whereas the first
55 oxidation was likely localized on N,N-dimethylamino donor, the
the first oxidation and reduction were further recalculated to
23
afford energies EHOMO and ELUMO
,
that can be compared with
60 the calculated HOMO and LUMO levels.
All target chromophores showed one or more one-electron
oxidation processes that are mostly reversible. The first oxidation
potential is within the range of +0.99 to +0.58 V. Within the
particular series of compound 1-3, the first oxidation potentials
65 decreased in the following order: a > d > b > c. With the same
donor and acceptor moieties and type of the BA connection to the
-linker, this observation reflects the composition and spatial
arrangement of the -linker. Whereas the planar stilbene -linkers
4
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Page 6 of 12
in chromophores c allowed very efficient D-A interaction
(E1/2(ox1) = +0.58 to +0.59 V), the N,N-dimethylamino donors in 60 consistent with those measured for previous N,N-dialkylamino
3.5–64.8×103 mol-1dm3cm-1 (Table 2). These values are
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DOI: 10.1039/C3NJ00683B
chromophores a and b with short 1,4-phenylene (E1/2(ox1) = +0.81
substituted BA derivatives.12
to +0.99 V) and twisted 4,4’-biphenylene -linkers
Table 1 Electrochemical data of chromophores 1-3
5
(E1/2(ox1) = +0.76 to +0.77 V) were engaged in less ICT. In
contrary to stilbene -linkers in c, the planar phenylethynylphenyl
-linkers in chromophores d shifted the first oxidation potential
anodically by about 200 mV up to +0.80 V. This clearly shows
the difference between the electronegative and insulating
E1/2(ox1) E1/2(red1)
EHOMO ELUMO
E
Comp.
[V]a [V]a
[eV]c [eV]c
[V]b
+0.99 -1.26 2.25 -5.42 -3.17
+0.77 -1.02 1.79 -5.20 -3.41
+0.58 -1.01 1.59 -5.01 -3.42
+0.79 -0.95 1.74 -5.22 -3.48
+0.81 -1.04 1.85 -5.24 -3.39
+0.76 -0.92 1.68 -5.19 -3.51
+0.59 -0.93 1.52 -5.02 -3.50
+0.78 -0.83 1.61 -5.21 -3.60
+0.94 -0.97 1.91 -5.37 -3.46
+0.77 -0.87 1.64 -5.20 -3.56
+0.58 -0.87 1.45 -5.01 -3.56
+0.80 -0.79 1.59 -5.23 -3.64
1a
1b
1c
1d
2a
2b
2c
2d
3a
3b
3c
3d
10 acetylenic and polarizable olefinic units.2,21d A comparison of
structural analogues 1b/2b/3b, 1c/2c/3c and 1d/2d/3d revealed
almost the same values of the first oxidation potentials +0.76 to
+0.77, +0.58 to +0.59 and +0.78 to +0.80 V. This indicates that
N,N-dimethylamino donors are in these sets of compounds
15 similarly involved in the ICT. However, compounds 1a/2a/3a
with the shortest 1,4-phenylene -linkers showed the expected
trend in the first oxidation potentials (+0.99/+0.81/+0.94 V). The
first oxidation potential decreased with increasing the overall
-system length and polarizability.
20 N,N’-Dibutylbarbituric acid can be denoted as the main reduction
centre of chromophores 1-3. The observed first reductions were
one-electron irreversible processes with E1/2(red1) ranging from -
1.26 to -0.79 V. The measured first reduction potentials were
again dependent on the structure and length of the -linker.
25 Within the particular series of compound 1-3, the values of
E1/2(red1) were shifted to more positive values in the following
order: d > c > b > a. This observation is in accordance with the
previous discussion on their oxidations. Thus, the most positively
shifted first reduction potentials -0.79 to -0.83 V were measured
30 for planar chromophores d with phenylethynylphenyl -linker. A
combination of two electronegative acetylenic units as in 3d
caused shift of E1/2(red1) up to -0.79 V. Whereas the first reduction
potentials of chromophores b and c were almost identical, the
most negative first reduction potentials were measured for
35 chromophores a. A comparison across three series 1-3 showed
that the first reductions are facilitated with increasing the length
and planarity of the -linker as well as on its connection to the
acceptor.
a E1/2(ox1) and E1/2(red1) are the half-wave potentials of the first oxidation and
reduction, respectively, as measured by RDV.
65 b E = E1/2(ox1) - E1/2(red1); the potentials are given versus SCE.
c EabsHOMO/LUMO = E1/2(ox1/red1) + 4.43.
Fig. 3 Energy level diagram of chromophores 1-3
Table 2 Optical properties of chromophores 1-3
The difference between the first oxidation and reduction
40 potentials E (electrochemical gap) assesses the D-A interaction
and the extent of the ICT in the best way. The data and energy
level diagram in Table 1 and Fig. 3 show a clear trend in
decreasing E in the order 1 > 2 > 3 and within each series in the
order a > b > d > c. Chromophores 1c (E = 1.59 V), 2c
45 (E = 1.52 V) and 3c (E = 1.45 V) showed the lowest
electrochemical gaps, mainly due to their raised HOMO level.

max [nm(eV)]/
 (×10-3) [mol-1 dm3cm-1]
Cyclohexane Dichloromethane Acetonitrile
Comp.
439(2.82)/63.7a 462 (2.68)/64.8 459(2.70)/45.7
444(2.79)/25.1a 467(2.66)/23.7 451(2.75)/10.5
476(2.61)/35.8a 493(2.52)/31.0 472(2.63)/13.5
450(2.76)/16.1a 460(2.70)/13.9 438(2.83)/3.50
495(2.51)/39.6b 527(2.35)/49.4 516(2.40)/53.0
460(2.70)/26.2 481(2.58)/34.4 467(2.66)/35.5
487(2.55)/36.8 508(2.44)/38.3 490(2.53)/42.8
454(2.73)/22.4 470(2.64)/32.4 449(2.76)/16.9
481(2.58)/34.6c 503(2.47)/26.6 491(2.53)/28.8
458(2.71)/34.3a 476(2.61)/23.4 458(2.71)/23.2
486(2.55)/25.5a 501(2.48)/30.9 479(2.59)/29.5
456(2.72)/27.3a 467(2.66)/21.7 444(2.79)/16.6
1a
1b
1c
1d
2a
2b
2c
2d
3a
3b
3c
3d
UV/Vis spectra
All target chromophores 1-3 are coloured compounds. Their
electronic absorption spectra were measured in three solvents
50 with different properties – cyclohexane (nonpolar, protic),
dichloromethane (nonpolar, aprotic, polarizable) and acetonitrile
(dipolar, aprotic, nonpolarizable) at a concentration of 2 × 10-5 M.
All spectra are shown in Fig. 4 and Fig. S7-S8 (the ESI). The
optical properties are summarized in Table 2. The measured
55 spectra in all solvents are dominated by intensive longest-
wavelength absorption CT-bands with max appearing between
439-495 (cyclohexane), 462-527 (dichloromethane) and 438–516
nm (acetonitrile). The molar absorption coefficients range from
a Indistinguishable shoulder.
70 b Shoulder at  = 476 nm ( = 41.6×103 mol-1 dm3cm-1).
c Shoulder at  = 454 nm ( = 26.6×103 mol-1 dm3cm-1).
Except for chromophores 1a and 1b, the max values of
chromophores 1-3 measured in cyclohexane and dichloromethane
are linearly dependent. The slope calculated by orthogonal linear
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New Journal of Chemistry
fit is 1.305 (Fig. S9, the ESI). A similar but less tight dependence
CT-bands. However, in comparison with 1a are the positions of
can be derived from the correlation between the max values 60 the longest-wavelength absorption maxima of 2a and 3a shifted
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measured in cyclohexane and acetonitrile (slope = 1.518; Fig
S10, the ESI). These slope values imply that a bathochromic shift
of the longest-wavelength absorption maxima is being observed
when going from nonpolar aprotic cyclohexane to polarizable
bathochromically as a result of their exDteOnId: 1e0d.103-l9i/nCk3eNrsJ0. 0A683B
comparison of structurally similar chromophores 1c/1d, 2c/2d
5
and 3c/3d reveals bathochromically shifted CT-bands (max
=
34–41 nm) for chromophores in series c that feature olefinic
dichloromethane or dipolar acetonitrile. This can be explained as 65 subunit (stilbene). This observation is in agreement with the
a higher solvation stabilization of the excited than the ground
state. This further implies that the excited state is more
10 polarizable and polar (most probably the dominant feature) than
the ground state.
previous findings made by electrochemistry. Cinnamaldehyde-
derived chromophores 2a-d showed the most bathochromically
shifted CT-bands (max = 449–516 nm) across tree series 1-3,
which reflects their planar and most polarizable connection of the
70 -linker to the BA acceptor via but-1,3-diene spacer.
Calculations and EFISH experiment
The calculations were performed with PM3 and PM7 semi-
empirical methods implemented in programs ArgusLab24 and
MOPAC201225 and visualization in OPchem.26 Energies of
75 HOMO and LUMO, their difference E, dipole moment  and
first hyperpolarizabilities  were calculated (Table 3). Although
the PM7 calculated values of EHOMO and ELUMO are in absolute
values different from those measured by CV and RDV, they
showed similar trends. Namely, the lowest calculated HOMO-
80 LUMO differences within the series of compounds 1-3 were
calculated for chromophores 1c (E = -6.76 eV), 2c (E = -6.40
eV) and 3c (E = -6.50 eV) with planar stilbene -linker.
15
20
25
30
35
40
45
50
85
Fig. 5 Optimized geometries and HOMO (red) and LUMO (blue)
localizations in chromophores 2a (a), 2b (b), 2c (c) and 2d (d)
Fig. 4 UV/Vis absorption spectra of chromophores in series 1-3 measured
in acetonitrile (c = 2 × 10-5 M)
As can be seen from these selected values, a connection of the
BA acceptor to the -system in 2 through but-1,3-diene spacer
allowed the most efficient D-A interaction. Hence, these
90 cinnamaldehyde-derived chromophores generally showed the
lowest HOMO-LUMO gap. Localization and gradual separation
The following structure-property relationships were deduced
55 from the spectra measured in acetonitrile (the solvent used for
electrochemical measurements). Chromophores 1a (max = 459
nm), 2a (max = 516 nm) and 3a (max = 491 nm) featuring the
shortest -linkers showed remarkably bathochromically shifted
6
| Journal Name, [year], [vol], 00–00
This journal is © The Royal Society of Chemistry [year]

New Journal of Chemistry
Page 8 of 12
olefinic subunits into the -linker (2c vs. 1a) enhanced the NLO
of the HOMO and the LUMO can be visualized on compounds
2a-d (Fig. 5). For complete listing of the HOMO/LUMO
localizations see Fig. S11–S22 in the ESI. As expected, the
HOMO is localized on the N,N-dimethylanilino donor moiety,
whilst the LUMO is spread over the barbituric acid C5 and
adjacent part of the -linker. This is in agreement with the
aforementioned electrochemical conclusions.
response seven times.
View Article Online
DOI: 10.1039/C3NJ00683B
50 Conclusions
5
N,N-Dimethylamino
donor-substituted
benzaldehydes,
cinnamaldehydes and propargyl aldehydes with systematically
extended -system were prepared and efficiently combined with
N,N’-dibutylabarbituric acid acceptor via Al2O3-catalyzed
55 Knoevenagel condensation. Twelve new push-pull chromophores
were synthesized and the extent of the ICT was further evaluated
by X-ray analysis, electrochemistry, absorption spectra,
calculation and EFISH experiment. With the given electron donor
and acceptor, the electrochemical, optical and NLO behaviour of
60 charge-transfer chromophores 1-3 can be finely tuned by
extension, composition and spatial arrangement of the -linker
used. Push-pull chromophore 2c showed well balanced properties
Table 3 Calculated and measured parameters of chromophores 1-3
EHOMO ELUMO
E
(2)


Comp.
[eV]a [eV]a
[eV]a [D]a [1029 esu]a [1048 esu]b
-8.52 -1.23 -7.29 7.47
-8.26 -1.36 -6.90 5.54
-8.13 -1.37 -6.76 5.92
-8.14 -1.29 -6.85 5.97
-8.36 -1.49 -6.87 7.93
-8.25 -1.65 -6.60 6.56
-8.08 -1.68 -6.40 7.73
-8.10 -1.64 -6.46 7.66
-8.55 -1.42 -7.13 7.03
-8.32 -1.56 -6.76 6.68
-8.10 -1.60 -6.50 8.12
-8.37 -1.61 -6.76 5.94
2.97
3.04
4.33
4.09
6.35
5.99
10.6
8.97
3.22
4.13
8.15
5.08
270
1080
1390
750
1000
1040
1880
1270
900
1a
1b
1c
1d
2a
2b
2c
2d
3a
3b
3c
3d
such as electrochemical gap E
= 1.52 V, the most
bathochromically shifted CT-band appearing at 490 nm (2.53
65 eV), calculated HOMO-LUMO difference (-6.40 eV), dipole
moment  = 7.73 D and thermal stability (mp 228-232 °C).
Considering the highest first hyperpolarizability  attained for
(T)BA derivatives (~300×10-30 esu) known to date and relatively
small -system of 2c, its calculated ( = 10.6×10-29 esu) and
70 measured NLO responses ( = 1880×10-48 esu) are remarkable.
In conclusion, N,N’-dibutylbarbituric acid proved to be very
efficient electron acceptor moiety in push-pull chromophores
assuring their large dipolar character and simultaneously
maintaining their sufficient solubility in common organic
940
1270
870c
a The data were calculated by PM7 (MOPAC2012). b Measured at 1907
10 nm in CHCl3, c was within the range 10-3 to 10-2 M; µ  10%.
c Underestimated due to aggregation.
Second-order non-linear optical properties were studied in CHCl3
solution by the electric-field-induced second-harmonic generation
technique (EFISH) which provides information about the scalar
15 product µ(2) of the vector component of the first
hyperpolarisability tensor  and the dipole moment vector.27 This 75 solvents. In view of the current interest in new organic materials
product is derived according to equation 1 and considering the
third-order term 0(-2,,,0) as negligible for the push-pull
compounds under study. This approximation is usually used for
20 push-pull organic and organometallic molecules.
for
optoelectronics
and
ease
of
its
synthesis,
N,N’-dibutylbarbituric acid can be regarded as an alternative to
former BA derivatives.
Experimental

EFISH = µ/5kT + 0(-2,,,0)
(1)
80 For more synthetic details and instrumentation used see the
Electronic Supplementary Information. All cross-coupling
reactions were carried out in Schlenk flasks dried under vacuum
and filled with argon.
Measurements were performed at 1907 nm, obtained from a
25 Raman-shifted Nd:YAG+ laser source, which allowed us to work
far from the resonance peaks of 1-3. It should be noted that the
sign and values of µ depend on the “direction” of the transition
implied in the NLO phenomena and on the direction of the
ground-state dipole moment. When  and µ were parallel
30 (antiparallel), positive (negative), maximal µ values were
reached. All the µβ values of compounds 1-3 (Table 3) are
positive which indicates more polarized excited than ground
states (µe > µg). In addition, this implies that the ground and
excited states are polarized in the same direction. The µβ values
35 observed are relatively high compared to Disperse Red 1 used as
NLO standard.28
General method for Suzuki-Miyaura reaction (Method A)
85 Iodo derivative (1.0 mmol) and boron ester 12 (259 mg, 1.05
mmol) were dissolved in the 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 (159 mg, 1.5
mmol) were added and the reaction mixture was stirred at 60 °C
90 for 12 h. The reaction was diluted with aq. NH4Cl (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 chromatography (SiO2;
CH2Cl2).
A comparison of measured µβ values with the calculated first
hyperpolarizabilities β in Table 2 revealed that both quantities
correspond in general trends. Namely, the highest /
40 coefficients were calculated/measured for NLOphores in series 2.
Both coefficients increased within the particular series in the
order of a > b > d > c. This observed variation in nonlinear
optical properties mimics the trends seen in the values of E and
95 General method for Heck reaction (Method B)
Iodo derivative (1.0 mmol) and styrene 13 (155 mg, 1.05 mmol)
were dissolved in toluene (30 ml) and iPr2NH (0.21 ml, 1.5
mmol) was added. Argon was bubbled through the solution for 15
min whereupon [Pd(P-tBu3)2] (28 mg, 0.04 mmol) was added and

max. The highest µβ value (1880×10-48 esu) was measured for
45 NLOphore 2c with the planar and polarizable stilbene -linker,
while NLOphore 1a showed the weakest NLO response
(270×10-48 esu). Thus, an insertion of one 1,4-phenylene and two 100 the reaction mixture was stirred at 80 °C for 12 h. The reaction
was diluted with aq. NH4Cl (50 ml) and extracted with CH2Cl2
This journal is © The Royal Society of Chemistry [year]
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Page 9 of 12
New Journal of Chemistry
Chromophore 1c
(2×50 ml). The combined organic extracts were dried (Na2SO4),
the solvents were evaporated in vacuo and the crude product was
purified by column chromatography (SiO2; CH2Cl2).
Compound 1c was synthesized from aldehyde 18 (251 mg, 1.0
DOI: 10.1039/C3NJ00683B
mmol) and N,N’-dibutylbarbituric acid (480 mg, 2.0 mmol). The
View Article Online
crude product was purified by repeated washing with hexane.
60 Compound 1c was isolated as a violet solid (364 mg, 77 %). Mp
172–177 °C. Rf = 0.63 (SiO2; CH2Cl2). Found: C, 72.78; H, 7.34;
N, 8.75. C29H35N3O3 requires C, 73.54; H, 7.45; N, 8.87%. IR
General method for Sonogashira reaction (Method C)
5
Iodo derivative (1.0 mmol) and acetylene 14 (152 mg, 1.05
mmol) were dissolved in THF (20 ml) and Et3N (5 ml). Argon
was bubbled through the solution for 15 min whereupon
[PdCl2(PPh3)2] (21 mg, 0.03 mmol) and CuI (6 mg, 0.03 mmol)
were added and the reaction mixture was stirred at 25 °C for 12 h.
10 The reaction was diluted with aq. NH4Cl (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 chromatography (SiO2;
CH2Cl2).
1
(HATR): max/cm-1 2921, 2360, 1714, 1657, 1363, 789. H NMR
(400 MHz; CDCl3): H 0.93–0.98 (6H, m, 2×CH3), 1.34–1.42
65 (4H, m, 2×CH2), 1.59–1.68 (4H, m, 2×CH2), 3.00 (6H, s,
N(CH3)2), 3.94–3.99 (4H, m, 2×NCH2), 6.70 (2H, d, J = 8.8,
CHar), 6.92 (1H, d, J = 16.0, CH), 7.22 (1H, d, J = 16.0, CH),
7.44 (2H, d, J = 8.8, CHar), 7.53 (2H, d, J = 8.4, CHar), 8.17 (2H,
d, J = 8.4, CHar) and 8.49 (1H, s, CH). 13C NMR (100 MHz,
70 CDCl3): C 14.01, 20.38, 20.43, 30.35, 40.51, 41.96, 42.54,
112.40, 116.06, 123.10, 124.95, 125.82, 128.82, 131.02, 132.97,
135.57, 144.01, 150.88, 151.11, 158.67, 160.73 and 162.90. HR-
15 General method for Knoevenagel reaction
A mixture of N,N’-dibutylbarbituric acid (240/480 mg, 1.0/2.0
mmol), aldehyde (1.0 mmol), Al2O3 (510 mg, 5.0 mmol, activity
II–III) and Na2SO4 (710 mg, 5.0 mmol) in CH2Cl2 (10 ml) was
stirred at 25 °C for 12 h. The suspension was filtered and the
20 solvent was evaporated in vacuo. The crude product was purified
by column chromatography (SiO2; CH2Cl2) or by washing with
hexane.
+
FT-MALDI-MS (DHB) m/z: 474.2752 ([M+H]+), C29H36N3O3
requires 474.2751.
75 Chromophore 1d
Compound 1d was synthesized from aldehyde 21 (249 mg, 1.0
mmol) and N,N’-dibutylbarbituric acid (480 mg, 2.0 mmol). The
crude product was purified by repeated washing with hexane.
Compound 1d was isolated as a red-violet solid (353 mg, 75 %).
80 Mp 139–143 °C. Rf = 0.63 (SiO2; CH2Cl2). Found: C, 74.05; H,
7.12; N, 8.86. C29H33N3O3 requires C, 73.86; H, 7.05; N, 8.91%.
IR (HATR): max/cm-1 2957, 2360, 1712, 1667, 1362, 1221, 1093.
1H NMR (400 MHz; CDCl3): H 0.93–0.98 (6H, m, 2×CH3),
1.37–1.41 (4H, m, 2×CH2), 1.58–1.64 (4H, m, 2×CH2), 3.01 (6H,
85 s, N(CH3)2), 3.93–3.99 (4H, m, 2×NCH2), 6.66 (2H, d, J = 8.8,
CHar), 7.42 (2H, d, J = 8.8, CHar), 7.53 (2H, d, J = 8.4, CHar),
8.11 (2H, d, J = 8.4, CHar) and 8.49 (1H, s, CH). 13C NMR (100
MHz, CDCl3): C 14.00, 20.38, 20.42, 30.35, 40.37, 42.04, 42.62,
88.19, 96.11, 109.37, 111.95, 117.30, 129.70, 131.01, 131.57,
90 133.37, 134.34, 150.71, 151.02, 158.19, 160.54 and 162.62. HR-
Chromophore 1a
Compound 1a was synthesized from commercially available
25 aldehyde 24 (149 mg, 1.0 mmol) and N,N’-dibutylbarbituric acid
(240 mg, 1.0 mmol). Compound 1a was isolated as an orange-red
solid (300 mg, 81 %). Mp 156–161 °C. Rf = 0.67 (SiO2; CH2Cl2).
Found: C, 67.47; H, 7.92; N, 11.21. C21H29N3O3 requires C,
67.90; H, 7.87; N, 11.31%. IR (HATR): max/cm-1 2921, 2359,
30 1712, 1645, 1362, 1090, 1017, 787. 1H NMR (400 MHz; CDCl3):
H 0.92–0.96 (6H, m, 2×CH3), 1.34–1.40 (4H, m, 2×CH2), 1.60–
1.64 (4H, m, 2×CH2), 3.13 (6H, s, N(CH3)2), 3.94–3.98 (4H, m,
2×NCH2), 6.69 (2H, d, J = 9.2, CHar), 8.37 (2H, d, J = 9.2, CHar)
and 8.42 (1H, s, CH). 13C NMR (100 MHz, CDCl3): C 14.01,
35 14.04, 20.41, 20.47, 30.43, 30.46, 40.26, 41.69, 42.28, 110.32,
111.20, 121.32, 139.57, 151.53, 154.47, 158.86, 161.56 and
163.96. HR-FT-MALDI-MS (DHB) m/z: 372.2281 ([M+H]+),
C21H30N3O3+ requires 372.2282.
+
FT-MALDI-MS (DHB) m/z: 472.2583 ([M+H]+), C29H34N3O3
requires 472.2595.
Chromophore 2a
Compound 2a was synthesized from commercially available
95 aldehyde 25 (175 mg, 1.0 mmol) and N,N’-dibutylbarbituric acid
(240 mg, 1.0 mmol). Compound 2a was isolated as a dark violet
solid (338 mg, 85 %). Mp 169–171 °C. Rf = 0.46 (SiO2; CH2Cl2).
Found: C, 69.34; H, 7.85; N, 10.39. C23H31N3O3 requires C,
69.49; H, 7.86; N, 10.57%. IR (HATR): max/cm-1 2923, 2360,
Chromophore 1b
40 Compound 1b was synthesized from aldehyde 15 (225 mg, 1.0
mmol) and N,N’-dibutylbarbituric acid (480 mg, 2.0 mmol). The
crude product was purified by repeated washing with hexane.
Compound 1b was isolated as a red-violet solid (219 mg, 49 %).
Mp 166-172 °C. Rf = 0.65 (SiO2; CH2Cl2). Found: C, 71.90; H,
45 7.38; N, 9.46. C27H33N3O3 requires C, 72.46; H, 7.43; N, 9.39%.
IR (HATR): max/cm-1 2922, 2360, 1712, 1654, 1363, 806.1H
NMR (400 MHz; CDCl3): H 0.93–0.98 (6H, m, 2×CH3), 1.40–
1.44 (4H, m, 2×CH2), 1.59–1.68 (4H, m, 2×CH2), 3.02 (6H, s,
N(CH3)2), 3.94–3.99 (4H, m, 2×NCH2), 6.78 (2H, d, J = 8.8,
50 CHar), 7.60 (2H, d, J = 8.8, CHar), 7.67 (2H, d, J = 8.8, CHar),
8.22 (2H, d, J = 8.4, CHar) and 8.54 (1H, s, CH). 13C NMR (100
MHz, CDCl3): C 13.99, 20.39, 20.43, 30.36, 40.52, 41.97, 42.55,
112.68, 116.20, 125.56, 127.01, 128.19, 130.39, 135.58, 146.32,
150.94, 151.12, 159.02, 160.75 and 162.90. HR-FT-MALDI-MS
55 (DHB) m/z: 448.2588 ([M+H]+), C27H34N3O3+ requires 448.2595.
1
100 1713, 1648, 1533, 1366, 1223, 1164, 809. H NMR (400 MHz;
CDCl3): H 0.93–0.97 (6H, m, 2×CH3), 1.33–1.41 (4H, m,
2×CH2), 1.59–1.64 (4H, m, 2×CH2), 3.08 (6H, s, N(CH3)2), 3.91–
3.95 (4H, m, 2×NCH2), 6.65 (2H, d, J = 8.8, CHar), 7.37 (1H, d, J
= 14.8, CH), 7.58 (2H, d, J = 8.8, CHar), 8.16 (1H, d, J = 12.4,
105 CH) and 8.41 (1H, dd, J1 = 12.4, J2 = 14.8, CH). 13C NMR (100
MHz, CDCl3): C 14.01, 14.03, 20.39, 20.49, 30.43, 30.50, 40.33,
41.41, 41.92, 110.53, 112.01, 120.82, 123.66, 132.30, 151.53,
153.14, 157.09, 158.69, 162.35 and 162.94. HR-FT-MALDI-MS
(DHB) m/z: 398.2436 ([M+H]+), C23H32N3O3+ requires 398.2438.
110 Chromophore 2b
8
| Journal Name, [year], [vol], 00–00
This journal is © The Royal Society of Chemistry [year]

New Journal of Chemistry
Page 10 of 12
Compound 2b was synthesized from aldehyde 16 (251 mg, 1.0
mmol) and N,N’-dibutylbarbituric acid (240 mg, 1.0 mmol).
mmol) and N,N’-dibutylbarbituric acid (240 mg, 1.0 mmol).
Compound 2b was isolated as a dark violet solid (431 mg, 91 %).
Compound 3a was isolated as a dark violet solid (304 mg, 77 %).
Mp 144–148 °C. Rf = 0.70 (SiO2; CH2ClD2)O. IF: 1o0u.n1d03: 9C/,C36N9J.70056;8H3B,
View Article Online
Mp 199–204 °C. Rf = 0.18 (SiO2; CH2Cl2/Hex 1:1). Found: C, 60 7.41; N, 10.54. C23H29N3O3 requires C, 69.85; H, 7.39; N,
5
73.34; H, 7.57; N, 8.69. C29H35N3O3 requires C, 73.54; H, 7.45;
10.62%. IR (HATR): max/cm-1 2923, 2360, 1713, 1362, 1258,
1222, 1090, 1014, 794. H NMR (400 MHz; CDCl3): H 0.92–
0.97 (6H, m, 2×CH3), 1.33–1.41 (4H, m, 2×CH2), 1.58–1.65 (4H,
m, 2×CH2), 3.07 (6H, s, N(CH3)2), 3.91–3.95 (4H, m, 2×NCH2),
1
N, 8.87%. IR (HATR): max/cm-1 2924, 2360, 1713, 1653, 1550,
1
1361, 1222, 809. H NMR (400 MHz; CDCl3): H = 0.93–0.98
(6H, m, 2×CH3), 1.35–1.42 (4H, m, 2×CH2), 1.59–1.65 (4H, m,
2×CH2), 3.01 (6H, s, N(CH3)2), 3.92–3.96 (4H, m, 2×NCH2), 65 6.65 (2H, d, J = 8.8, CHar), 7.58 (2H, d, J = 8.8, CHar) and 7.81
10 6.78 (2H, d, J = 7.2, CHar), 7.42 (1H, d, J = 15.2, CH), 7.56 (2H,
d, J = 7.2, CHar), 7.61 (2H, d, J = 8.4, CHar), 7.69 (2H, d, J = 8.4,
CHar), 8.19 (1H, d, J = 12.0, CH) and 8.61 (1H, dd, J1 = 15.2, J2 =
12.0, CH). 13C NMR (100 MHz, CDCl3): C 14.00, 14.02, 20.38,
(1H, s, CH). 13C NMR (100 MHz, CDCl3): C 13.96, 13.98,
20.36, 20.41, 30.34, 40.24, 41.59, 42.12, 94.03, 107.99, 111.77,
121.56, 125.55, 136.29, 137.35, 151.17, 152.53, 159.92 and
161.90. HR-FT-MALDI-MS (DHB) m/z: 396.2275 ([M+H]+),
20.47, 30.37, 30.43, 40.58, 41.63, 42.13, 112.74, 113.98, 124.50, 70 C23H30N3O3+ requires 396.2282.
15 126.50, 127.33, 127.95, 130.12, 133.12, 144.60, 150.72, 151.25,
Chromophore 3b
154.65, 157.70, 161.87 and 162.43. HR-FT-MALDI-MS (DHB)
m/z: 474.2727 ([M+H]+), C29H36N3O3+ requires 474.2725.
Compound 3b was synthesized from aldehyde 17 (249 mg, 1.0
mmol) and N,N’-dibutylbarbituric acid (240 mg, 1.0 mmol).
Compound 3b was isolated as a dark violet solid (382 mg, 81 %).
Chromophore 2c
Compound 2c was synthesized from aldehyde 19 (277 mg, 1.0 75 Mp 179–184 °C. Rf = 0.77 (SiO2; CH2Cl2). Found: C, 73.66; H,
20 mmol) and N,N’-dibutylbarbituric acid (240 mg, 1.0 mmol).
Compound 2c was isolated as a dark violet solid (400 mg, 80 %).
Mp 228–232 °C. Rf = 0.73 (SiO2; CH2Cl2). Found: C, 74.42; H,
7.57; N, 8.37. C31H37N3O3 requires C, 74.52; H, 7.46; N, 8.41%.
7.02; N, 8.90. C21H33N3O3 requires C, 73.86; H, 7.05; N, 8.91%.
IR (HATR): max/cm-1 2928, 2360, 1717, 1658, 1567, 1556, 1398,
1363, 1291, 808. 1H NMR (400 MHz; CDCl3): H 0.93–0.98 (6H,
m, 2×CH3), 1.32–1.44 (4H, m, 2×CH2), 1.58–1.68 (4H, m,
IR (HATR): max/cm-1 2923, 2360, 1715, 1656, 1543, 1396, 1361, 80 2×CH2), 3.01 (6H, s, N(CH3)2), 3.92–3.97 (4H, m, 2×NCH2),
1
25 1221, 821. H NMR (400 MHz; CDCl3): H 0.93–0.98 (6H, m,
2×CH3), 1.36–1.40 (4H, m, 2×CH2), 1.59–1.65 (4H, m, 2×CH2),
2.99 (6H, s, N(CH3)2), 3.92–3.96 (4H, m, 2×CH2), 6.69 (2H, d, J
= 8.8, CHar), 6.89 (1H, d, J = 16.0, CH), 7.15 (1H, d, J = 16.0,
6.78 (2H, d, J = 8.8, CHar), 7.55 (2H, d, J = 8.4, CHar), 7.61 (2H,
d, J = 8.4, CHar), 7.70 (2H, d, J = 8.8, CHar) and 7.80 (1H, s, CH).
13C NMR (100 MHz, CDCl3): C 13.99, 14.01, 20.38, 20.43,
29.93, 30.33, 40.57, 41.82, 42.33, 91.41, 112.74, 119.02, 119.51,
CH), 7.37 (1H, d, J = 15.2, CH), 7.42 (2H, d, J = 8.8, CHar), 7.48 85 124.77, 126.16, 127.24, 128.02, 134.38, 136.73, 144.29, 150.77,
30 (2H, d, J = 8.4 Hz, CHar), 7.62 (2H, d, J = 8.4, CHar), 8.18 (1H, d,
J = 12.0, CH) and 8.55 (1H, dd, J1 = 15.2, J2 = 12.0, CH). 13C
NMR (100 MHz, CDCl3): C 13.99, 14.02, 20.38, 20.47, 30.37,
30.43, 40.54, 41.63, 42.13, 112.45, 113.93, 123.21, 124.54,
125.15, 126.67, 128.30, 130.03, 131.65, 133.76, 142.14, 150.70,
35 151.24, 154.45, 157.61, 161.88 and 162.42. HR-FT-MALDI-MS
(DHB) m/z: 500.2893 ([M+H]+), C31H38N3O3+ requires 500.2908.
150.92, 159.44 and 161.40. HR-FT-MALDI-MS (DHB) m/z:
472.2589 ([M+H]+), C29H34N3O3+ requires 472.2595.
Chromophore 3c
Compound 3c was synthesized from aldehyde 20 (275 mg, 1.0
90 mmol) and N,N’-dibutylbarbituric acid (240 mg, 1.0 mmol).
Compound 3c was isolated as a dark violet solid (408 mg, 82 %).
Mp 207–212 °C. Rf = 0.83 (SiO2; CH2Cl2). Found: C, 74.69; H,
7.16; N, 8.36. C31H35N3O3 requires C, 74.82; H, 7.09; N, 8.44%.
Chromophore 2d
Compound 2d was synthesized from aldehyde 22 (275 mg, 1.0
mmol) and N,N’-dibutylbarbituric acid (240 mg, 1.0 mmol). 95 1222, 825. H NMR (400 MHz; CDCl3): H 0.93–0.98 (6H, m,
IR (HATR): max/cm-1 2922, 2360, 1713, 1659, 1565, 1400, 1362,
1
40 Compound 2d was isolated as a dark violet solid (378 mg, 76 %).
Mp 194–199 °C. Rf = 0.85 (SiO2; CH2Cl2). Found: C, 74.28; H,
7.08; N, 8.36. C31H35N3O3 requires C, 74.82; H, 7.09; N, 8.44%.
2×CH3), 1.34–1.42 (4H, m, 2×CH2), 1.59–1.66 (4H, m, 2×CH2),
2.98 (6H, s, N(CH3)2), 3.90–3.96 (4H, m, 2×NCH2), 6.68 (2H, d,
J = 8.8, CHar), 6.87 (1H, d, J = 16.0, CH), 7.13 (1H, d, J = 16.0,
CH), 7.40 (2H, d, J = 8.8, CHar), 7.47 (2H, d, J = 8.4, CHar), 7.62
IR (HATR): max/cm-1 2922, 2360, 1713, 1653, 1558, 1397, 1362,
1
1222, 816. H NMR (400 MHz; CDCl3): H 0.93–0.98 (6H, m, 100 (2H, d, J = 8.4, CHar) and 7.78 (1H, s, CH). 13C NMR (100 MHz,
45 2×CH3), 1.32–1.42 (4H, m, 2×CH2), 1.57–1.65 (4H, m, 2×CH2),
3.00 (6H, s, N(CH3)2), 3.92–3.96 (4H, m, 2×NCH2), 6.65 (2H, d,
J = 8.8, CHar), 7.37 (1H, d, J = 15.6, CH), 7.41 (2H, d, J = 8.8,
CHar), 7.50 (2H, d, J = 8.0, CHar), 7.62 (2H, d, J = 8.0, CHar),
CDCl3): C 13.92, 13.96, 20.31, 20.37, 30.25, 40.46, 41.74,
42.24, 91.76, 112.37, 119.41, 119.50, 123.03, 124.59, 124.96,
126.21, 128.29, 131.97, 134.24, 136.52, 141.72, 150.66, 150.84,
159.38 and 161.32. HR-FT-MALDI-MS (DHB) m/z: 498.2740
8.18 (1H, d, J = 12.0, CH) and 8.59 (1H, dd, J1 = 15.6, J2 = 12.0, 105 ([M+H]+), C31H36N3O3+ requires 498.2751.
50 CH). 13C NMR (100 MHz, CDCl3): C 13.99, 14.01, 20.37, 20.46,
30.36, 30.42, 40.37, 41.69, 42.18, 87.96, 95.17, 109.48, 111.96,
Chromophore 3d
Compound 3d was synthesized from aldehyde 23 (273 mg, 1.0
114.77, 125.50, 127.80, 129.26, 131.89, 133.20, 134.32, 150.58,
151.17, 153.46, 157.14, 161.77 and 162.30. HR-FT-MALDI-MS
(DHB) m/z: 498.2741 ([M+H]+), C31H36N3O3+ requires 498.2751.
mmol) and N,N’-dibutylbarbituric acid (240 mg, 1.0 mmol).
Compound 3d was isolated as a dark violet solid (342 mg, 69 %).
110 Mp 190–195 °C. Rf = 0.71 (SiO2; CH2Cl2). Found: C, 75.10; H,
6.80; N, 8.49. C31H33N3O3 requires C, 75.13; H, 6.71; N, 8.48%.
IR (HATR): max/cm-1 2922, 2360, 1715, 1675, 1654, 1567, 1400,
55 Chromophore 3a
Compound 3a was synthesized from aldehyde 11 (173 mg, 1.0
This journal is © The Royal Society of Chemistry [year]
Journal Name, [year], [vol], 00–00 | 9

Page 11 of 12
New Journal of Chemistry
1360, 1094, 789. 1H NMR (400 MHz; CDCl3): H 0.93–0.97 (6H,
m, 2×CH3), 1.32–1.43 (4H, m, 2×CH2), 1.57–1.67 (4H, m,
2×CH2), 3.00 (6H, s, N(CH3)2), 3.92–3.96 (4H, m, 2×NCH2),
6.65 (2H, d, J = 8.8, CHar), 7.41 (2H, d, J = 8.8, CHar), 7.50 (2H,
d, J = 8.4, CHar), 7.63 (2H, d, J = 8.4, CHar) and 7.78 (1H, s, CH).
13C NMR (100 MHz, CDCl3): C 13.95, 13.98, 20.35, 20.40,
29.91, 30.30, 40.35, 41.85, 42.35, 87.71, 91.58, 95.49, 109.36,
111.96, 117.71, 120.45, 125.45, 127.65, 131.50, 133.21, 133.58,
136.26, 150.64, 150.85, 159.34 and 161.26. HR-FT-MALDI-MS
8
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Acknowledgement
This work was supported by the Czech Science Foundation
(13-01061S) and Technology Agency of the Czech Republic
(TE01020022, Flexprint).
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