Imidazole as a donor/acceptor unit in charge-transfer chromophores with extended π-linkers

Article abstract of DOI:10.1002/asia.201100097

Eleven new, stable, push-pull systems that feature 4,5-bis[4-(N,N- dimethylamino)phenyl]imidazole and 4,5-dicyanoimidazole as the donor and acceptor moieties and the systematically extended and varied π-linker were prepared and investigated. Evaluation of the measured UV/Vis spectra, electrochemical data (cyclic voltammetry (CV), rotating-disc voltammetry (RDV), and polarography) and calculated β and γ polarizabilities showed efficient charge transfer (CT) in biimidazole-type chromophores. Push-pull system 27, which features a planar thiophene-derived π-linker, was revealed to be the most efficient chromophore within the studied series. This chromophore possessed the most bathochromically shifted CT band, the lowest electrochemical gap, and highest β and γ polarizabilities. The CT transition was most significantly affected by structural features such as π-linker length, planarity, conjugating arrangement, and the presence of olefinic/acetylenic or 1,4-phenylene/thiophene subunits in the π-linker. Copyright

Full text of DOI:10.1002/asia.201100097

FULL PAPERS
DOI: 10.1002/asia.201100097
Imidazole as a Donor/Acceptor Unit in Charge-Transfer Chromophores with
Extended p-Linkers
Jirˇꢀ Kulhꢁnek,[a] Filip Buresˇ,*[a] Oldrˇich Pytela,[a] Tomꢁsˇ Mikysek,[b] and Jirˇꢀ Ludvꢀk[c]
Abstract: Eleven new, stable, push–pull
systems that feature 4,5-bis[4-(N,N-di-
lated b and g polarizabilities showed
efficient charge transfer (CT) in biimi-
dazole-type chromophores. Push–pull
system 27, which features a planar thio-
phene-derived p-linker, was revealed
to be the most efficient chromophore
within the studied series. This chromo-
phore possessed the most bathochromi-
cally shifted CT band, the lowest elec-
trochemical gap, and highest b and g
polarizabilities. The CT transition was
most significantly affected by structural
features such as p-linker length, planar-
ity, conjugating arrangement, and the
presence of olefinic/acetylenic or 1,4-
phenylene/thiophene subunits in the p-
linker.
methylamino)phenyl]imidazole
and
4,5-dicyanoimidazole as the donor and
acceptor moieties and the systematical-
ly extended and varied p-linker were
prepared and investigated. Evaluation
of the measured UV/Vis spectra, elec-
trochemical data (cyclic voltammetry
Keywords: charge transfer · conju-
gation · donor–acceptor systems ·
electrochemistry · imidazoles
(CV),
rotating-disc
voltammetry
(RDV), and polarography) and calcu-
Introduction
light-emitting diodes (OLED), and organic photovoltaic
cells.[1–3] A typical organic D-p–A chromophore consists of
strong electron donors (D) and acceptors (A) linked
through a p-conjugated system, which ensures intramolecu-
lar charge transfer between the donor and acceptor moiet-
ies.[4,5] The polarizability of these push–pull systems depends
primarily on its chemical structure, in particular, the elec-
tronic behavior of the appended donors and acceptors and
the length of the p-conjugated linker.[6] Variously substituted
organic molecules have previously been investigated as po-
tentially NLO-active materials. However, strong electron-
donating substituents such as N,N-dialkylamino (NR2) and
alkoxy (OR), in addition to strong electron-withdrawing
moieties including nitro (NO2) and cyano (CN) functionali-
ties, are the most common groups used to generate dipolar
push–pull systems that feature low-energy and intense CT
absorption. Modern organic chromophores differ primarily
in the p-linkers that connect both donor and acceptor moi-
eties. Thus, various p-conjugated bridges, including triple or
double bonds,[7,5a] aromates,[8] heteroaromates,[9] and various
combinations, have been utilized as suitable p-linkers. In
general, a heteroaromate incorporated into the chromo-
phore backbone increases polarizability, stability, and ther-
mal and chemical robustness required for fabrication pro-
cesses. Heteroatoms might also act as auxiliary donors or ac-
ceptors. We have recently shown that the application of sub-
stituted imidazole as a p-conjugated backbone provided effi-
cient and robust D-p–A chromophores.[10] 4,5-Donor- or
In recent years, an impressive amount of attention has been
devoted to the development of various organic D-p–A sys-
tems because of their highly polarizable structures and re-
sulting efficient intramolecular charge transfer (CT). In con-
trast to inorganic materials, organic materials with readily
polarizable push–pull systems have been recognized as tuna-
ble chromophores for nonlinear optics (NLO) and have
found widespread application as two-photon absorbing devi-
ces, optoelectronic and optical data storage devices, organic
ˇ
[a] Prof. J. Kulhꢀnek, Prof. F. Bures, Prof. O. Pytela
Institute of Organic Chemistry and Technology
Faculty of Chemical Technology
University of Pardubice
Studentskꢀ 573, Pardubice, 53210 (Czech Republic)
Fax : (+420)46-603-7068
E-mail: filip.bures@upce.cz
[b] Dr. T. Mikysek
Department of Analytical Chemistry
Faculty of Chemical Technology
University of Pardubice
Studentskꢀ 573, Pardubice, 53210 (Czech Republic)
[c] Prof. J. Ludvꢁk
J. Heyrovsky Institute of Physical Chemistry
Academy of Science of the Czech Republic, v.v.i.
Dolejskova 3, Prague 8, 18223 (Czech Republic)
ˇ
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201100097.
1604
ꢂ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2011, 6, 1604 – 1612

acceptor-disubstituted imidazoles were used either as donor
(series a) or acceptor moieties (series b) to generate Y-
shaped push–pull chromophores with a systematically ex-
tended p-conjugated path.
Results and Discussion
Synthesis
The retrosynthetic strategy that led to target chromophores
18–24 and 26–29 involved a facile, one-pot condensation of
4,4’-bis(N,N-dimethylamino)benzil with extended and func-
tionalized aldehydes. The reaction proceeded in the pres-
ence of ammonium acetate in glacial acetic acid, similar to
the construction of the parent 4,5-bis[4-(N,N-dimethylami-
no)phenyl]imidazole (Scheme 1).[10e] Starting aldehydes 1, 4,
and 6 were commercially available, and the extended and
functionalized aldehydes 2, 3, 5, and 7, needed to be synthe-
sized. The reaction of aldehydes 1, 4, and 6 with one equiva-
lent of (triphenylphosphoranylidene)acetaldehyde[11] afford-
ed cinnamaldehyde analogues 2, 5, and 7 with yields of 54,
51, and 64%, respectively (see the Supporting Information).
Aldehyde 3 was synthesized from 4-bromobenzaldehyde by
Sonogashira cross-coupling with trimethylsilylacetylene[12]
followed by TMS group removal (K2CO3/MeOH) and a
final Sonogashira cross-coupling with 4-iodophenylboronic
acid pinacol ester.[13] Subsequent N-methylation (lithium
bis(trimethylsilyl)amide (LHMDS)/MeI) furnished inter-
mediates 8–14 (Scheme 1, see the Supporting Information).
Since the first synthesis of 4,5-dicyanoimidazole reported
by Woodward in 1950,[14] this heterocyclic compound
became a popular acceptor moiety for the construction of
various push–pull systems.[15] Reagents including 1-methyl-
4,5-dicyanoimidazole (15), 1-methyl-2-vinyl-4,5-dicyanoimi-
dazole (16, 1-methylvinazene),[16] and 2-bromo-1-methyl-4,5-
dicyanoimidazole (17)[14b,10b] were utilized as useful synthetic
precursors in this respect. Cross-coupling reactions of 15–17
with chromophore units 8–12 led to target chromophores
18–24 (Scheme 2). Transition-metal-mediated direct C-aryla-
tion[17] of 15 with 8 afforded the simplest target chromo-
phore 18 with a modest yield of 17%. On the contrary, pal-
ladium-catalyzed Heck olefination[15f] of iodo derivatives 8
and 9 with 1-methylvinazene 16 afforded target chromo-
phores 19 and 20 with yields of 69 and 45%, respectively.
Whereas chromophore 21 was easily synthesized by a
Suzuki–Miyaura cross-coupling between 10 and 17 (42%
yield), chromophore 22, which contained a central biphenyl
linker, was obtained from 1-methylvinazene 16 through se-
quential cross-coupling reactions. 1-Methylvinazene 16 was
treated with 4-iodophenylboronic acid pinacol ester follow-
ing a Heck olefination to yield intermediate 25 (see the Sup-
porting Information). A subsequent Suzuki–Miyaura reac-
tion between dioxaborolane 25 and derivative 8 afforded
chromophore 22 in 56% yield. Similar to the syntheses of
chromophores 19 and 20, triimidazole chromophores 23 and
24 were prepared using a twofold palladium-catalyzed Heck
olefination of dibromo intermediates 11 and 12 with 16 with
yields of 23 and 48%, respectively. In contrast to the synthe-
sis of target chromophore 18, the direct C-arylation of imi-
dazole 15 with halogenated intermediates 9, 11, and 12 did
not afford the desired product.
In the work presented, we have employed both donor/ac-
ceptor imidazole moieties in the construction of chromo-
phores 18–24 and 26–29. The second generation of imida-
zole-derived push–pull systems features 4,5-bis[4-(N,N-dime-
thylamino)phenyl]imidazole
(D=N,N-dimethylanilino,
DMA) as a donor and 4,5-dicyanoimidazole (A=CN) as an
acceptor moiety. Both chromophore units are linked at the
imidazole C2 positions by a systematically extended and
varied p-linker. To prevent 1H-imidazole tautomerism, both
imidazole rings were further N-methylated (R=Me).
Herein, we wish to report the synthetic strategy used to
obtain target chromophores 18–24 and 26–29, full spectral
characterization, and an investigation into the efficiency of
CT interactions in such biACTHNUTRGENU(GN tri)imidazole push–pull systems
by means of electrochemistry, optical spectroscopy, and
structure–property relationships.
ˇ
Abstract in Czech: Bylo pripraveno a dꢀle studovꢀno je-
˚
´
ˇ
denꢀct novych push-pull systꢃmu vyuzꢁvajꢁcꢁch 4,5-bis[4-
(N,N-dimethylamino)fenyl]imidazolu a 4,5-dikyanoimidazo-
lu jako donornꢁch a akceptornꢁch jednotek se systematicky
ˇ
ˇ
prodluzovanou p-konjugovanou cestou. Vyhodnocenꢁ zme-
ˇ
´
´
renych dat jako jsou UV/Vis spektra, elektrochemickych dat
ˇ
´
(CV, RDV a polarografie) a spocꢁtanych hodnot polarizabilit
ˇ
´
b a g ukꢀzalo efektivnꢁ prenos nꢀboje v bi-imidazolovych
˚
typech chromoforu. Push-pull systꢃm 27 nesoucꢁ planꢀrnꢁ p-
˚
ˇ ˇ
mustek na bꢀzi thiofenu se ukꢀzal jako nejefektivnejsꢁ chro-
mofor z celꢃ studovanꢃ sꢃrie. Tento chromofor vykazoval
ˇ
´
ˇˇ
nejvꢁce bathochromne posunuty CT pꢀs, nejnizsꢁ elektroche-
´
ˇˇ
ˇ
micky rozdꢁl a nejvyssꢁ hodnoty polarizabilit b a g. CT pre-
´
ˇ
ˇ
chod ve studovanych slouceninꢀch byl nejvꢁce ovlivnovꢀn
˚
strukturnꢁmi prvky jako jsou dꢃlka a planarita p-mustku,
ˇ
ˇ ˇ
ˇ
ˇ
prꢁtomnost
usporꢀdꢀnꢁ umoznujꢁcꢁ prꢁmou konjugaci
a
dvojnꢃ/trojnꢃ vazby resp. 1,4-fenylen/thiofen-2,5-diyl pod-
˚
Thiophene has been recently recognized as a useful p-
jednotek p-mustku.
linker and auxiliary donor.[18] Therefore, we were also inter-
Chem. Asian J. 2011, 6, 1604 – 1612
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ˇ
F. Bures et al.
FULL PAPERS
Scheme 1. Condensation of extended and functionalized aldehydes to imidazole intermediates 8–14.
Scheme 2. Cross-coupling reactions that resulted in target bi- and tri-imidazoles with extended p-linkers.
ested in replacing the 1,4-phenylene p-linker with a thio-
phene unit. Intermediates 13 and 14 were further used for
the construction of target imidazole–thiophene–imidazole
chromophores 26–29 (Scheme 2). Unfortunately, the direct
C-arylation of imidazole 15 with bromo intermediates 13
and 14 failed similarly to the aforementioned case of inter-
mediates 9, 11, and 12. However, Heck olefination of 13 and
14 with 1-methylvinazene 16 yielded chromophores 26 and
27 in 47 and 31% yield, respectively. Chromophore 28 was
synthesized successively through a Sonogashira cross-cou-
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Chem. Asian J. 2011, 6, 1604 – 1612

Charge-Transfer Chromophores
Table 1. Electrochemical data for chromophores 18–24 and 26–29 mea-
sured by CV, RDV, and polarography.
pling between 13 and commercially available 4-ethynylphe-
nylboronic acid pinacol ester (30) (see the Supporting Infor-
mation). A final Suzuki–Miyaura cross coupling between 30
and 17 afforded the desired chromophore 28 in 42% yield.
Chromophore 29 was synthesized from dioxaborolane 25
and intermediate 13 with a Suzuki–Miyaura cross-coupling
in 32% yield.
Compound Eo
DEp
Ep
E =
1
1
E =
2
2
(CV)
(CV)
[mV][b]
(CV)
[V][c]
(RDV)
[V][d]
(polarography)
[V][d]
[V][a]
18
+0.72
+0.58
+0.28
À1.82
97
63
177
93
+0.74
+0.59
+0.37
À1.82
À1.81
À2.00
À2.25
À2.53
À2.65
À1.61
À1.98
À2.70
À1.56
À1.74
À1.85
À2.12
À1.73
À1.89
À2.56
Electrochemistry
19
20
+0.72
+0.56
À1.63
+0.69
+0.52
À1.57
79
70
69
71
60
123
+0.72
+0.56
À1.65
+0.71
+0.53
À1.60
Electrochemical measurements were carried out in N,N-di-
methylformamide that contained 0.1m Bu4NPF6 in a three-
electrode cell by cyclic voltammetry (CV) and rotating-disc
voltammetry (RDV). The working electrode was a platinum
disc (2 mm in diameter) for CV and RDV experiments and a
dropping mercury electrode (DME) for polarographic meas-
urements. A saturated calomel electrode (SCE) separated
by a bridge filled with supporting electrolyte and platinum
wire were used as the reference and auxiliary electrodes.
The acquired data is summarized in Table 1. Representative
CV and polarographic curves for compounds 18, 20, 23, and
27 are shown in the Supporting Information. Generally, the
first oxidation occurred on the donor chromophore unit,
whereas the first reduction involved the acceptor moiety
and the p-linker similar to previous investigations.[10b,e] All
studied chromophores showed two reversible one-electron
oxidation processes with potentials that ranged from +0.52
to +0.58 and +0.69 to +0.74 V, and a nearly constant differ-
ence of 150 mV. This electrochemical behavior reflected the
presence of two nonequivalent N,N-dimethylamino donor
groups appended to imidazole C4/C5. Similar to the electro-
chemical behavior of previous chromophores in series a
(4,5-bis[4-(N,N-dimethylamino)phenyl]imidazole as donor
moiety), the oxidation potentials of chromophores 18–24
and 26–29 were negligibly affected by the structure of the p-
linker. However, chromophores 20, 24, and 27, which fea-
tured full-planar p-linkers with all imidazole and benzene
rings linked through double bonds, were oxidized at the
lowest potentials. The simplest chromophore (18) was an ex-
ception. In addition to the two aforementioned oxidation
processes at +0.58 and +0.72 V, chromophore 18 showed an
additional significant quasireversible oxidation process at
+0.28 V (DEp =177 mV). The RDV experiment confirmed a
one-electron oxidation process. In contrast to 19–24 and 26–
29, chromophore 18, which contained two imidazole moiet-
ies connected through a 1,4-phenylene unit, can be oxidized
to a quinoid system,[19] which might rationalize the observa-
tion.
À1.80
21
22
+0.74
+0.58
À1.72
À1.93
+0.71
66
59
64
97
74
+0.74
+0.57
+0.71
À1.61
+0.56
À1.62
65
66
+0.57
À1.63
À1.96
À2.37
À2.65
À1.54
À1.65
À2.01
À2.67
À1.54
À2.04
23
24
+0.74
+0.58
73
67
+0.74
+0.58
À1.64
+0.73
+0.71
À1.60
+0.56
À1.60
À1.64
À1.99
À2.34
À1.54
À1.89
À2.60
À1.41
À1.63
À2.24
À2.45
À1.69
À1.86
À2.67
26
27
+0.73
+0.57
À1.56
+0.69
+0.54
À1.41
69
65
108
60
61
78
+0.72
+0.57
À1.58
+0.70
+0.55
À1.43
À1.73
+0.74
+0.59
À1.71
À1.87
+0.70
+0.56
À1.56
28
29
+0.74
+0.58
À1.69
À1.86
+0.69
+0.55
À1.56
60
60
140
135
72
À1.56
À1.84
À1.20
À2.22
À2.50
60
83
[a] Eo =(Ep,c+Ep,a)/2, for which Ep,c and Ep,a correspond to the cathodic
and anodic peak potentials, respectively. [b] DEp =EoxÀEred (reversible
1
redox process). [c] Ep =irreversible peak potential. [d] E = =half-wave po-
2
tential measured by RDV or polarography.
Three to five reduction processes were observed for 18–24
and 26–29 at the DME (potential window up to À2.8 V).
The first reduction was likely localized on 4,5-dicyanoimida-
zole, and the subsequent reductions involved the p-linker.
However, the first reductions were one-electron and mostly
reversible processes. The first reduction potentials ranged
from À1.41 to À1.81 V and were dependent upon the length
and structure of the p-linker. For example, the first reduc-
tion potentials in the series 18–20 changed from À1.81 to
À1.56 V as a result of elongation and planarization of the
central p-linker. On the other hand, chromophores 21 and
22, which contained phenylethynylphenyl and biphenyle-
thenyl p-linkers, were reduced at À1.71 and À1.61 V due to
their nonplanar arrangement[10b] and the fact that the triple
bond could act as an insulator.[7a,10c] Both tri-imidazole chro-
mophores 23 and 24, which possessed two 4,5-dicyanoimida-
zole units, were reduced at À1.54 V. Taking into consider-
ation the presence of two acceptor moieties, the reduction
Chem. Asian J. 2011, 6, 1604 – 1612
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F. Bures et al.
FULL PAPERS
Table 2. Absorption maxima (lmax); electrochemical gaps D(Eox,1ÀEred,1);
calculated energies EHOMO, ELUMO; and average second and third polariz-
abilities b and g for chromophores 18–24 and 26–29.
potentials were more negative than expected relative to 20.
However, this result can be rationalized due to the noncon-
jugating arrangement of the donor and acceptor moieties
(1,3,5-trisubstitution of the central benzene ring). The first
oxidation potentials of chromophores 26–29, which feature
thiophene as a part of the p-linker, ranged from À1.41 to
À1.69 V. These chromophores were reduced at more posi-
tive potentials relative to the corresponding chromophores
(19 and 20) that contained 1,4-phenylene unit (e.g.,
Ered,1(20)=À1.57 and Ered,1(27)=À1.41 V). From the electro-
chemical perspective, the D–A interaction through the 2,5-
disubstituted thiophene proved to be more efficient than
through the 1,4-phenylene unit.
Compound
lmax
D(Eox,1ÀEred,1
)
EHOMO ELUMO bꢄ1029 gꢄ1027
[eV] [eV] [esu] [esu]
G
[V]
N
ACHTUNGTRENNUNG
18
19
20
21
22
23
24
26
27
28
29
366 (3.39)
404 (3.07)
444 (2.79)
373 (3.32)
382 (3.25)
316 (3.92)
394 (3.15)
448 (2.77)
479 (2.59)
413 (3.00)
420 (2.95)
2.39
2.17
2.08
2.31
2.17
2.12
2.10
2.11
1.95
2.27
2.11
À7.77 À1.14 3.82
À7.73 À1.25 3.82
À7.66 À1.31 6.60
À7.65 À1.30 4.48
À7.65 À1.27 3.84
À7.90 À1.41 2.55
À7.85 À1.41 3.96
À7.75 À1.10 29.90
À7.65 À1.51 52.63
À8.23 À1.43 8.22
À7.75 À1.28 4.79
3.61
5.17
8.99
6.26
5.78
4.51
5.97
164.05
315.15
45.91
20.18
UV/Vis Spectroscopy
UV/Vis spectra of chromophores 18–22 and 26–29 measured
in dichloromethane showed more or less intense CT absorp-
tion bands (Figure 1, Table 2). The CT character of the lon-
gest-wavelength bands was confirmed by protonation/neu-
tralization experiments[7a] with trifluoroacetic acid/triethyla-
mine (for compounds 20 and 27 see the Supporting Informa-
tion). Tri-imidazole chromophores 23 and 24 showed a weak
CT absorption as a result of the nonconjugating arrange-
ment. However, the longest-wavelength absorption maxima
(lmax) of the individual, systematically extended series of
compounds 18 (lmax =366 nm), 19 (lmax =404 nm), and 20
(lmax =444 nm) showed a clear bathochromic shift as a result
of the p-linker elongation and molecule planarization
through the double-bond insertion. Compared to 19 and 20,
the lmax of chromophores 21 and 22 (lmax =373 and 382 nm)
lacked planarity or possessed electronegative triple bond
were shifted hypsochromically.
All chromophores that featured thiophene as a part of the
p-linker (26–29) showed well-developed CT bands with the
lmax appearing between 413 and 479 nm. Planar chromo-
phore 27 (lmax =479 nm), which contained two imidazole
and thiophene moieties separated by double bonds, showed
the most bathochromically shifted CT band within the stud-
ied series of compounds. A comparison of the lmax of chro-
mophores 19 and 26 (lmax =404 vs. 448 nm), 20 and 27
(lmax =444 vs. 479 nm), 21 and 28 (lmax =373 vs. 413 nm),
and 22 and 29 (lmax =382 vs. 420 nm) with the molecular
structure varying only in the 1,4-phenylene or thiophene p-
linker subunits provided another indication of the efficiency
of the intramolecular CT. This behavior is in accordance
with the electrochemical observations.
Calculations
The optimized geometries of all possible planar conformers
of compounds 18–24 and 26–29 were calculated by PM3
(ArgusLab)[20]
and,
subsequently,
PM6
methods
(MOPAC2009).[21] The most stable conformers were selected
on the basis of their minimal total energy calculated by
MOPAC2009 and are shown in Scheme 2. The performed
calculations revealed important structural features. The
DMA moiety appended to the imidazole C4 was twisted out
of the imidazole plane to a lesser degree (the dihedral angle
ranged from 23 to 308, typically 278) than the DMA moiety
at the imidazole C5 (the dihedral angles were 62–738, typi-
Figure 1. UV/Vis spectra of chromophores 18–24 and 26–29 (2ꢄ10À5
solutions in CH2Cl2).
m
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Chem. Asian J. 2011, 6, 1604 – 1612

Charge-Transfer Chromophores
cally 658). These results imply that the donor moiety is neg-
ligibly affected by the chromophore residue appended at C2
and that the DMA at C4 is the dominant electron donor.
The ethylene linker appended to imidazole C2 (both accept-
or- or donor-substituted imidazoles) caused molecule plana-
rization (maximal dihedral angle was 138, typically less than
58). The methyl group appended to imidazole N1 and the
closest hydrogen atom of the double bond at imidazole C2
were always oriented on the same side. The thiophene and
the ethylene subunits in chromophores 26 and 27 were co-
planar. The data implies that the ethylene linker is a very
useful structural element that elongates and makes the p-
conjugated system planar. On the other hand, the phenylene
linker (1,4- or 1,3-disubstituted) represents a steric and elec-
tronic barrier of an efficient D–A conjugation (the dihedral
angles ranged from 44 to 578). In contrast to benzene, the
more polarizable five-membered thiophene ring featured
lower steric interactions, and therefore the dihedral angles
between imidazole and thiophene in 26 and 29 were 278 and
38 for 28.
In addition, the HOMO and LUMO energies and average
second and third polarizabilities b and g were further calcu-
lated (Table 2). Representative HOMO and LUMO locali-
zations for compounds 20, 24, and 27 are shown in the Sup-
porting Information. Table 2 shows mutual relationships be-
tween the measured optical, electrochemical, and calculated
chromophore properties. The influence of the p-linker on
the D–A conjugations can be clearly demonstrated in the
series 18–22 and 26–29 in which the D–A separation was
systematically extended and varied. Both the electrochemi-
cal D(Eox,1ÀEred,1) and optical gaps (eV) decreased in the
following order: 18, 21, 22, 19, 20, and 28, 29, 26, 27. More-
over, the highest values of g and b polarizabilities were cal-
culated for imidazole–thiophene–imidazole chromophores
27 and 26.
culated average second and third polarizabilities, b (52.63ꢄ
10À29 esu) and g (315.15ꢄ10À27 esu). Among the studied
chromophores, the p-linker of 27, which contained polariza-
ble double bonds and thiophene subunits, appeared to be
optimal. In view of the considerable thermal (e.g., m.p. (27)
ꢀ2808C) and chemical robustness of all studied compounds,
their second-order optical nonlinearities and application as
components for NLO device fabrication is now being inves-
tigated.
Experimental Section
General
Reagents and solvents were reagent-grade and were purchased from
Penta, Aldrich, and Acros and used as received. Starting aldehydes 1, 4,
and 6 are commercially available. The synthesis of aldehydes 2, 3, 5, and
7 are found in the Supporting Information. The condensation reactions
were carried out in a sealed glass pressure tube (Aldrich). The general
method for condensation reaction including N-alkylation and full spectral
characterization of intermediates 8–14, 25, and 30 are found in the Sup-
porting Information. Compounds 15–17 were synthesized according to
the literature.[10b,14b,16] Column chromatography was carried out with silica
gel 60 (particle size 0.040–0.063 mm, 230–400 mesh; Merck) and commer-
cially available solvents. Thin-layer chromatography (TLC) was conduct-
ed on aluminum sheets coated with silica gel 60 F254, obtained from
Merck, with visualization by a UV lamp (254 or 360 nm). Melting points
(m.p.) were measured with a Bꢅchi B-540 melting-point apparatus in
1
open capillaries and were uncorrected. H and 13C NMR spectra were re-
corded at 400 and 100 MHz, respectively, with a Bruker AVANCE 400
instrument at 258C. Chemical shifts are reported in ppm relative to the
1
signal of Me4Si. The residual solvent signal in the H and 13C NMR spec-
tra was used as an internal reference (CDCl3 7.25 and 77.23 ppm;
[D6]DMSO 2.55 and 39.51 ppm). Apparent resonance multiplicities are
described as s (singlet), brs (broad singlet), d (doublet), dd (doublet of
doublet), and m (multiplet). Protons of the N,N-dimethylanilino groups
at C4/C5 were marked as DMA. IR spectra were recorded with a
Perkin–Elmer FTIR Spectrum BX spectrometer. Mass spectra were mea-
sured with a GC-MS configuration comprised of an Agilent Technologies
6890N gas chromatograph equipped with a 5973 Network MS detector
(EI 70 eV, mass range 33–550 Da) or on an LC-MS Micromass Quattro
Micro API (Waters) instrument with a direct input (ESI, CH3OH, mass
range 200–1000 Da). Elemental analyses were performed with an EA
1108 Fisons instrument. UV/Vis spectra were recorded with a Hewlett–
Packard 8453 spectrophotometer in CH2Cl2.
Conclusion
A series of eleven new and stable D-p–A systems were pre-
pared in which the 4,5-bis[4-(N,N-dimethylamino)phenyl]i-
midazole and 4,5-dicyanoimidazole were used as donor and
acceptor, respectively. The p-linker between these moieties
was systematically extended and varied to investigate its in-
fluence on the chromophore properties. The most important
structural features that affected intramolecular CT were:
1) the length of the p-conjugated path; 2) the conjugating
arrangement of the p-linker; 3) the overall chromophore
planarity; and 4) the presence of olefinic/acetylenic and 1,4-
phenylene/thiophene subunits. Considering the measured
and calculated properties, chromophore 27 appeared to be
exceptional. Although 27 did not possess the largest p-
linker, the planar, fully conjugated molecule allowed effi-
cient D–A interactions. Chromophore 27 possessed the most
bathochromically shifted CT band with lmax appearing at
479 nm (2.59 eV), the lowest electrochemical gap (1.95 V),
the difference EHOMOÀELUMO (6.14 eV), and the largest cal-
General Method for Direct C-Arylation (Compound 18)
Imidazole 15 (46 mg, 0.35 mmol), intermediate 8 (146 mg, 0.28 mmol),
and DMF (5 mL) were placed in a flame-dried Schlenk flask under
argon. Argon was bubbled trough the resulting solution for 10 min,
whereupon PdACHTNUGTRENUNG(OAc)2 (3.2 mg, 0.014 mmol), CuI (107 mg, 0.56 mmol),
and CsF (85 mg, 0.56 mmol) were successively added, and the reaction
mixture was stirred at 1408C for 12 h. The reaction was cooled to 258C
and quenched with aqueous NH4Cl (sat.). The reaction was extracted
with EtOAc (3ꢄ30 mL), the combined organic layers were dried
(Na2SO4), and the solvent was evaporated. The crude product was puri-
fied by column chromatography (silica gel; CH2Cl2/acetone 15:1). Yield:
25 mg (17%), orange solid. Rf =0.25 (silica gel; CH2Cl2/acetone 15:1);
m.p. 174–1778C; 1H NMR (400 MHz, CDCl3, 258C): d=2.91 (s, 6H; N-
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
R
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
258C): d=29.88, 34.04, 40.40, 40.53, 110.90, 111.95, 112.32, 112.45, 114.54,
116.17, 121.11, 122.34, 127.95, 128.89, 129.83, 130.10, 131.46, 131.59,
Chem. Asian J. 2011, 6, 1604 – 1612
ꢂ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
1609

ˇ
F. Bures et al.
FULL PAPERS
131.75, 138.09, 146.19, 149.90, 150.67, 151.77 ppm; IR (neat): n˜ =2852,
2359 (CN), 2343 (CN), 1609, 1442, 1165, 942, 847, 821, 716 cmÀ1; MS
(ESI): m/z (%): 527 [M++H]; elemental analysis calcd (%) for C32H30N8
(526.6): C 72.98, H 5.74, N 21.28; found C 73.00, H 5.77, N 21.29.
ACHTUNGTRENNUNG
General Method for Heck Olefination (Compounds 19, 20, 23, 24, 26,
and 27)
1-Methylvinazene 16 (33 or 66 mg, 0.21 or 0.42 mmol), iodo or bromo in-
termediates 8, 9, 13, or 14 (0.20 mmol), or dibromo intermediates 11 or
12 (0.20 mmol), DMF (5 mL), and diisopropylethylamine (0.2 mL) were
placed in a flame-dried Schlenk flask under argon. Argon was bubbled
Compound 24
The title compound was synthesized from 16 (66 mg, 0.42 mmol) and 12
(116 mg, 0.20 mmol) following the general procedure. Yield: 70 mg
(48%), orange solid. Rf =0.30 (silica gel; CH2Cl2/acetone 10:1); m.p.
3108C (decomp); 1H NMR (400 MHz, [D6]DMSO, 258C): d=2.91 (s,
through the resulting solution for 10 min, whereupon [Pd{PACTHNUGTRNEUNG(tBu)3}2]
(10 mg, 0.02 mmol) was added, and the reaction was stirred at 858C for
12 h. The reaction was cooled to 258C, diluted with water, and extracted
with CH2Cl2 (3ꢄ30 mL). The combined organic extracts were washed
with water, dried (Na2SO4), and the solvent was evaporated. The crude
product was purified by column chromatography (silica gel; indicated sol-
vent system).
6H; N
NCH3), 6.65 (d, 3J
2H; DMA), 7.23 (d, 3J
8.8 Hz, 2H; DMA), 7.51–7.67 (m, 4H; CH), 7.85 (d, 3J
2H; CH), 8.18 (s, 1H; 1,3,5-Ar), 8.27 ppm (s, 2H; 1,3,5-Ar); 13C NMR
(100 MHz, [D6]DMSO, 258C): d=30.67, 33.12, (two N(CH3)2) signals at
G
ACHTUNGTRENNUNG
E
ACHTUNGTRENNUNG
G
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
Compound 19
around 40 ppm merged with DMSO), 109.10, 110.67, 111.18, 11.98,
112.23, 112.59, 112.95, 113.02, 113.10, 113.39, 113.44, 120.59, 121.85,
126.84, 126.95, 129.24, 131.43, 136.13, 137.54, 137.60, 148.87, 149.99,
150.07, 150.37 ppm; IR (neat): n˜ =2968, 2359 (CN), 2340 (CN), 1738,
1504, 1455, 1364, 1261, 1227, 1216, 1021, 817, 816, 668 cmÀ1; MS (ESI):
m/z (%): 735 [M++H]; elemental analysis calcd (%) for C44H38N12
(734.9): C 71.92, H 5.21, N 22.87; found C 71.95, H 5.20, N 22.85.
The title compound was synthesized from 16 (33 mg, 0.21 mmol) and 8
(104 mg, 0.20 mmol) following the general procedure. Yield: 76 mg
(69%), red solid. Rf =0.20 (silica gel; CH2Cl2/acetone 95:5); m.p. 186–
1898C; 1H NMR (400 MHz, CDCl3, 258C): d=2.90 (s, 6H; N
ACHTUNGTRENNUNG
3.02 (s, 6H; N
3J
(H,H)=8.8 Hz, 2H; DMA), 6.78 (d, J
(d, 3J(H,H)=15.6 Hz, 1H; CH), 7.23 (d, 3J
7.47 (d, J
phenylene), 7.80 (d, 3J
3J(H,H)=15.6 Hz, 1H; CH); 13C NMR (100 MHz, CDCl3, 258C): d=
ACHTUNGTRENNUNG
3
T
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
Compound 26
3
3
U
ACHTUNGTREN(NUNG H,H)=8.0 Hz, 2H; 1,4-
The title compound was synthesized from 16 (33 mg, 0.21 mmol) and 13
(96 mg, 0.20 mmol) following the general procedure. Yield: 52 mg (47%),
red solid. Rf =0.35 (silica gel; CH2Cl2/acetone 95:5); m.p. 280–2828C;
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
32.81, 33.50, 40.53, 40.77, 108.66, 110.25, 112.05, 112.50, 112.57, 112.97,
118.53, 122.64, 123.64, 127.78, 127.93, 129.39, 130.70, 131.91, 133.22,
134.46, 138.33, 140.12, 146.07, 149.30, 150.42, 150.65 ppm; IR (neat): n˜ =
2793, 2358 (CN), 2340 (CN), 1611, 1499, 1351, 1192, 1057, 943, 821,
668 cmÀ1; MS (ESI): m/z (%): 553 [M++H]; elemental analysis calcd
(%) for C34H32N8 (552.7): C 73.89, H 5.84, N 20.27; found C 73.64, H
5.79, N 20.20.
1H NMR (400 MHz, CDCl3, 258C): d=2.90 (s, 6H; N
ACHTUNGTRENNUNG
6H; NACHTGNUTRENNUNG
A
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
A
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
258C): d=32.73, 33.13, 40.51, 40.77, 108.74, 108.83, 112.06, 112.46, 112.58,
112.72, 117.91, 122.70, 123.27, 125.14, 127.79, 131.18, 131.99, 132.05,
133.12, 134.28, 137.04, 138.91, 139.73, 140.46, 149.43, 150.56 ppm; IR
(neat): n˜ =2893, 2359 (CN), 2340 (CN), 2230, 1738, 1605, 1528, 1498,
1451, 1392, 1354, 1219, 1189, 1062, 949, 822, 806, 668 cmÀ1; MS (ESI): m/
z (%): 559 [M++H]; elemental analysis calcd (%) for C32H30N8S (558.7):
C 68.79, H 5.41, N 20.06, S 5.74; found C 68.89, H 5.43, N 20.06, S 5.78.
Compound 20
The title compound was synthesized from 16 (33 mg, 0.21 mmol) and 9
(110 mg, 0.20 mmol) following the general procedure. Yield: 52 mg
(45%), dark red solid. Rf =0.25 (silica gel; CH2Cl2/acetone 10:1); m.p.
287–2918C; 1H NMR (400 MHz, CDCl3, 258C): d=2.90 (s, 6H; N-
G
ACHTUNGTRENNUNG(CH3)2), 3.49 (s, 3H; NCH3), 3.80 (s, 3H; NCH3),
Compound 27
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
The title compound was synthesized from 16 (33 mg, 0.21 mmol) and 14
(101 mg, 0.20 mmol) following the general procedure. Yield: 36 mg
(31%), dark red solid. Rf =0.35 (silica gel; CH2Cl2/acetone 10:1); m.p.
278–2828C; 1H NMR (400 MHz, CDCl3, 258C): d=2.91 (s, 6H; N-
ACHTUNGTRENNUNG
G
ACHTUNGTRENNUNG
16.0 Hz, 1H; CH); 13C NMR (100 MHz, CDCl3, 258C): d=31.07, 32.76,
40.54, 40.79, 108.73, 109.52, 112.05, 112.52, 112.56, 112.85, 115.57, 118.33,
122.65, 123.63, 127.42, 127.87, 128.02, 130.08, 130.35, 131.95, 134.14,
139.41, 140.20, 140.28, 144.21, 149.38, 150.44, 150.80 ppm; IR (neat): n˜ =
2891, 2359 (CN), 2340 (CN), 1613, 1526, 1454, 1348, 1196, 947, 810, 807,
668 cmÀ1; MS (ESI): m/z (%): 579 [M++H]; elemental analysis calcd
(%) for C36H34N8 (578.7): C 74.72, H 5.92, N 19.36; found C 74.80, H
5.96, N 19.42.
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
3
3
A
ACHTUNGTREN(NUNG H,H)=15.2 Hz,
AHCTUNGTRENNUNG
A
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
(100 MHz, CDCl3, 258C): d=30.97, 32.69, 40.55, 40.78, 108.39, 108.76,
111.32, 112.06, 112.51, 112.57, 112.74, 115.78, 122.73, 123.53, 127.85,
128.19, 130.36, 131.05, 131.80, 131.94, 132.51, 133.06, 138.75, 139.41,
143.66, 149.44, 150.46, 150.54 ppm; IR (neat): n˜ =3313, 2360 (CN), 2341
(CN), 1735, 1608, 1527, 1458, 1364, 1217, 1196, 939, 818, 668 cmÀ1; MS
(ESI): m/z (%): 585 [M++H]; elemental analysis calcd (%) for
C34H32N8S (584.7): C 69.84, H 5.52, N 19.16, S 5.48; found C 69.70, H
5.49, N 19.19, S 5.48.
Compound 23
The title compound was synthesized from 16 (66 mg, 0.42 mmol) and 11
(111 mg, 0.20 mmol) following the general procedure. Yield: 33 mg
(23%), yellow solid. Rf =0.20 (silica gel; CH2Cl2/acetone 10:1); m.p.
3208C (decomp); 1H NMR (400 MHz, [D6]DMSO, 258C): d=2.90 (s,
6H; N
NCH3), 6.64 (d, 3J
2H; DMA), 7.25 (d, 3J
9.0 Hz, 2H; DMA), 7.60 (d, 3J
(H,H)=16.0 Hz, 2H; CH), 8.20 (s, 2H; 1,3,5-Ar), 8.34 ppm (s, 1H; 1,3,5-
Ar); 13C NMR (100 MHz, [D6]DMSO, 258C): d=32.65, 33.18, (two N-
N
ACHTUNGTRENNUNG
G
ACHTUNGTRENNUNG
G
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
1610
www.chemasianj.org
ꢂ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2011, 6, 1604 – 1612

Charge-Transfer Chromophores
General Method for the Suzuki–Miyaura Cross-Coupling (Compounds
Compound 29
21, 22, 28, and 29)
The title compound was synthesized from 13 (120 mg, 0.25 mmol) and di-
oxaborolane 25 (94 mg, 0.26 mmol) following the general procedure.
Yield: 51 mg (32%), red solid. Rf =0.60 (silica gel; CH2Cl2/acetone 10:1);
m.p. 274–2778C; 1H NMR (400 MHz, CDCl3, 258C): d=2.90 (s, 6H; N-
Imidazole 17 (53 mg, 0.25 mmol) or intermediates 13 or 8 (0.25 mmol),
and dioxaborolanes 10, 25, or 30 (0.26 mmol) were dissolved in THF/
H2O (5 mL, 4:1). Argon was bubbled through the resulting solution for
10 min, whereupon [Pd
(PPh3)2Cl2] (18 mg, 0.025 mmol) and Na2CO3
ACHTUGTNRENUNG(CH3)2), 3.03 (s, 6H; NACTHUNGTRENNUNG
(32 mg, 0.3 mmol) were added, and the reaction was stirred at 658C for
2.5 h. The reaction was cooled to 258C, diluted with water, and extracted
with CH2Cl2 (3ꢄ30 mL). The combined organic extracts were washed
with water, dried (Na2SO4), and the solvent was evaporated. The crude
product was purified by column chromatography (silica gel; indicated sol-
vent system).
6.61 (d, 3J
A
3
3
7.21 (d, J
A
U
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
32.80, 33.09, 40.57, 40.80, 108.72, 109.64, 110.96, 112.02, 112.54, 112.60,
112.92, 116.81, 118.28, 122.72, 124.49, 126.27, 126.43, 127.83, 128.51,
128.57, 130.49, 132.04, 133.94, 136.09, 140.14, 140.96, 143.42, 149.37,
150.49, 150.74 ppm; IR (neat): n˜ =2968, 2359 (CN), 2340 (CN), 1738,
1614, 1504, 1361, 1226, 1216, 969, 946, 822, 794, 668 cmÀ1; MS (ESI): m/z
(%): 635 [M++H]; elemental analysis calcd (%) for C38H34N8S (634.8): C
71.90, H 5.40, N 17.65, S 5.05; found C 71.96, H 5.42, N 17.71, S 5.07.
Compound 21
The title compound was synthesized from 17 (53 mg, 0.25 mmol) and di-
oxaborolane 10 (162 mg, 0.26 mmol) following the general procedure.
Yield: 66 mg (42%), orange solid. Rf =0.33 (silica gel; CH2Cl2/acetone
10:1); m.p. 178–1828C; 1H NMR (400 MHz, CDCl3, 258C): d=2.90 (s,
6H; N
NCH3), 6.61 (d, 3J
2H; DMA), 7.24 (d, 3J
8.8 Hz, 2H; DMA), 7.63–7.70 (m, 4H; 1,4-phenylene), 7.78 ppm (d, 3J-
(H,H)=8.4 Hz, 2H; 1,4-phenylene); 13C NMR (100 MHz, CDCl3, 258C):
d=33.27, 34.79, 40.35, 40.61, 89.23, 92.49, 108.33, 111.65, 112.33, 112.39,
114.23, 122.29, 122.37, 123.86, 124.18, 126.31, 126.48, 126.89, 127.63,
128.84, 128.97, 130.22, 131.76, 131.90, 132.26, 134.78, 145.68, 149.16,
150.28, 151.82 ppm; IR (neat): n˜ =2192, 2359 (CN), 2339 (CN), 1738,
1613, 1496, 1455, 1362, 1227, 1216, 1056, 1013, 840, 819, 668 cmÀ1; MS
(ESI): m/z (%): 627 [M++H]; elemental analysis calcd (%) for C40H34N8
(626.75): C 76.65, H 5.47, N 17.88; found C 76.79, H 5.49, N 17.80.
G
ACHTUNGTRENNUNG
R
ACHTUNGTRENNUNG
G
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
Acknowledgements
This research was supported by the Czech Science Foundation (203/08/
0076) and the Ministry of Education, Youth, and Sport of the Czech Re-
public (MSM 0021627501).
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1245–1330.
Compound 22
The title compound was synthesized from 8 (130 mg, 0.25 mmol) and di-
oxaborolane 25 (94 mg, 0.26 mmol) following the general procedure.
Yield: 88 mg (56%), orange solid. Rf =0.21 (silica gel; CH2Cl2/acetone
10:1); m.p. 301–3058C; 1H NMR (400 MHz, CDCl3, 258C): d=2.90 (s,
[3] Y. Ohmori, Laser Photonics Rev. 2009, 4, 300–310.
6H; N
NCH3), 6.60 (d, 3J
DMA+CH), 7.21 (d, 3J
N
ACHTNUGTERN(NUGN CH3)2), 3.48 (s, 3H; NCH3), 3.73 (s, 3H;
[4] L. R. Dalton, J. Phys. Condens. Matter 2003, 15, R897-R934.
[5] a) J. Y. Lee, K. S. Kim, B. J. Mhin, J. Chem. Phys. 2001, 115, 9484–
9489; b) M. Kivala, F. Diederich, Acc. Chem. Res. 2009, 42, 235–
248; c) D. M. Burland, R. D. Miller, O. Reiser, R. J. Twieg, C. A.
Walsh, J. Appl. Phys. 1992, 71, 410–417; d) D. R. Kanis, M. A.
Ratner, T. J. Marks, Chem. Rev. 1994, 94, 195–242.
ACHTUNGTRENNUNG
G
ACHTUNGTRENNUNG
8.8 Hz, 2H; DMA), 7.57–7.68 (m, 6H; 1,4-phenylene), 7.77–7.82 ppm (m,
3H; 1,4-phenylene+CH); 13C NMR (100 MHz, CDCl3, 258C): d=32.79,
33.35, 40.55, 40.80, 108.69, 109.92, 112.02, 112.52, 112.58, 112.87, 118.81,
122.64, 123.84, 127.18, 127.74, 127.77, 128.39, 129.57, 130.13, 131.24,
131.96, 134.02, 138.01, 139.74, 140.27, 142.46, 146.52, 149.21, 150.38,
150.71 ppm; IR (neat): n˜ =2918, 2359 (CN), 2340 (CN), 2228, 1738, 1613,
1497, 1361, 1216, 1197, 1061, 965, 945, 823, 810, 668 cmÀ1; MS (ESI): m/z
(%): 629 [M++H]; elemental analysis calcd (%) for C40H36N8 (628.8): C
76.41, H 5.77, N 17.82; found C 76.55, H 5.80, N 17.87.
ˇ
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5378–5387; b) Y.-L. Wu, F. Bures, P. D. Jarowski, W. B. Schweizer,
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Compound 28
The title compound was synthesized from 17 (53 mg, 0.25 mmol) and di-
oxaborolane 30 (163 mg, 0.26 mmol) following the general procedure.
Yield: 66 mg (42%), orange solid. Rf =0.60 (silica gel; CH2Cl2/acetone
95:5); m.p. 271–2748C; 1H NMR (400 MHz, CDCl3, 258C): d=2.90 (s,
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Eur. J. Org. Chem. 2010, 1096–1110.
6H; N
NCH3), 6.60 (d, 3J
2H; DMA), 7.20 (d, 3J
Th), 7.44 (d, 3J
(H,H)=8.8 Hz, 2H; DMA), 7.61–7.68 ppm (m, 4H; 1,4-
G
ACHTUNGTRENNUNG
G
ACHTUNGTRENNUNG
[9] a) E. L. Spitler, L. D. Schirtcliff, M. M. Haley, J. Org. Chem. 2007,
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ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
phenylene); 13C NMR (100 MHz, CDCl3, 258C): d=33.03, 35.01, 40.53,
40.78, 86.29, 93.16, 108.54, 111.88, 112.49, 112.60, 114.43, 118.10, 122.48,
123.35, 125.29, 126.36, 126.47, 127.75, 129.17, 130.69, 131.99, 132.10,
133.42, 136.66, 138.58, 140.42, 149.38, 150.52, 151.93 ppm; IR (neat): n˜ =
2968, 2359 (CN), 2340 (CN), 1737, 1610, 1526, 1500, 1455, 1353, 1217,
1195, 942, 822, 806, 668 cmÀ1; MS (ESI): m/z (%): 633 [M++H]; elemen-
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5.07; found C 72.28, H 5.11, N 17.80, S 5.11.
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Received: February 1, 2011
Published online: May 19, 2011
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