Synthesis, multiphase characterization, and helicity control in chiral DACH-linked oligothiophenes

Article abstract of DOI:10.1002/chem.200600312

A new class of chiral oligothiophenes is described. Mono-, bi-, ter-, and quarterthiophenes have been linked to enantiopure trans-1,2-cyclohexanediamine (DACH) via diamino or diimino moieties. The stereochemistry of DACH, the type of linker, and oligothio

Full text of DOI:10.1002/chem.200600312

FULL PAPER
DOI: 10.1002/chem.200600312
7304
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2006, 12, 7304 – 7312

FULL PAPER
Synthesis, Multiphase Characterization, andHelicity Control in Chiral
DACH-LinkedOligothiophenes**
Manuela Melucci,*[a] Giovanna Barbarella,[a] Massimo Gazzano,[a]
Massimiliano Cavallini,[b] Fabio Biscarini,[b] Alessandro Bongini,[c] Fabio Piccinelli,[c]
[d]
Magda Monari,[c] Marco Bandini,[c] Achille Umani-Ronchi,[c] andPaolo Biscarini
Abstract: A new class of chiral oligo-
thiophenes is described. Mono-, bi-,
ter-, and quarterthiophenes have been
linked to enantiopure trans-1,2-cyclo-
hexanediamine (DACH) via diamino
or diimino moieties. The stereochemis-
try of DACH, the type of linker, and
oligothiophene size determine the con-
formational flexibility of these mole-
cules and consequently their molecular
and supramolecular helicity in solution
and in the solid state. The case of di-
aminobis(bithiophene), which inverts
helicity and shows chiral amplification
in the transition from solution to film,
is described in detail. Based on the
combined use of circular dichroism in
solution and in the solid state, single-
crystal/thin-film X-ray diffraction, and
polarized optical microscopy, a working
mechanism has been proposed to ex-
plain this unexpected behavior.
Keywords: chirality · helical struc-
tures
·
oligothiophenes
·
self-
assembly · thin films
Introduction
depend on a subtle interplay between intrinsic molecular
constraints and numerous noncovalent interactions such as
van der Waals interactions, weak hydrogen bonds, S–S inter-
actions, and p–p stacking.[6] Recently, the self-organizing be-
havior of chiral conjugated molecules in solution[7] and at
surfaces[8] has attracted a great deal of interest.[9] Concern-
ing oligothiophenes, Lecl›re et al. have studied the self-as-
sembly of two enantiomeric sexithiophenes on different sur-
faces and showed by comparison with an achiral counterpart
that the presence of stereocenters is required to obtain heli-
cal aggregates.[10] Nevertheless, the way in which the chirali-
ty of conjugated oligothiophenes is transferred from the mo-
lecular level to supramolecular assemblies in thin films still
remains unclear.
Some of us have recently reported on the use of the chiral
1,2-cyclohexandiamine scaffold (DACH)[11] to prepare a new
family of chiral diamino-oligothiophenes as valuable ligands
in palladium-catalyzed asymmetric transformations.[12] Trig-
gered by their peculiar skeleton motifs, in which multiple
specific active sites for noncovalent intra- and intermolecu-
lar interactions are present, we have now prepared oligo-
thiophenes up to tetramers linked to chiral DACH spacers
by diimine or diamine moieties and investigated the way
stereochemical and spatial constraints imposed by DACH
affect their self-organization in thin films.
Oligothiophenes are multifunctional materials of great inter-
est in organic electronics.[1] Their molecular organization
and morphology in thin films control charge transport and
light emission properties in technological devices.[2] Several
processing approaches ranging from organic molecular
beam deposition[3] to solution casting, nanopatterning,[4] and
mechanical manipulation[5] have been proposed to control
their thin-film organization across multiple length scales.
The mechanism of self-assembly and the kinetics of growth
[a] Dr. M. Melucci, Dr. G. Barbarella, Dr. M. Gazzano
Istituto per la Sintesi Organica e la Fotoreattività (ISOF)
Consiglio Nazionale Ricerche, Via Gobetti 101, 40129 Bologna (Italy)
Fax : (+39)516-398-349
E-mail: mmelucci@isof.cnr.it
[b] Dr. M. Cavallini, Dr. F. Biscarini
Istituto per lo Studio dei Materiali Nanostrutturati ISMN-Sez Bo
Consiglio Nazionale Ricerche, Via Gobetti 101, 40129 Bologna (Italy)
[c] Prof. Dr. A. Bongini, Dr. F. Piccinelli, Prof. Dr. M. Monari,
Dr. M. Bandini, Prof. Dr. A. Umani-Ronchi
Dipartimento di Chimica ꢁG. Ciamicianꢂ
Università di Bologna, via Selmi 2, 40126 Bologna (Italy)
[d] Prof. Dr. P. Biscarini
Dipartimento di Chimica Fisica e Inorganica
Università di Bologna, Viale Risorgimento 4, 40136 Bologna (Italy)
We demonstrate that in these compounds the oligothio-
phene side arms adopt a helical arrangement both in solu-
tion and in the solid state, the overall handedness being dic-
[**] DACH=trans-1,2-cyclohexanediamine.
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the author.
Chem. Eur. J. 2006, 12, 7304 – 7312
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
7305

M. Melucci et al.
tated by the stereochemistry of DACH, the side-arm length,
and the type of DACH–oligothiophene linker. We also show
how these parameters are related to the morphology ob-
served in cast films.
NaBH4 gave satisfactory results (88 and 75% yields, respec-
tively), while for the longer terthienyl derivative 3c,
NaBH3CN in the presence of dry HCl was needed to obtain
the diamino derivative 4c in reasonably good yield (44%
yield). However, to date, despite several attempts, we have
not been able to achieve the reduction of 3d.
Results
Conformational analysis: To obtain information for use in
aiding the analysis of experimental data, the conformational
preferences of DITn and DATn were investigated using the
semiempirical PM3 Hamiltonian which better describes the
thiophene structure.[13]
For both families of compounds the orientation of the two
arms can be either diequatorial or diaxial, and for each of
them the possible rotations
Synthesis of chiral oligothiophenes: The synthesis of the dii-
mino (DITn) and diamino (DATn) oligomers is summarized
in Scheme 1. DITn oligomers were obtained by condensing
formylated oligothiophenes and commercial R,R, S,S, or rac-
emic cyclohexanediamine (1) both by conventional heating
and microwave-assisted processes.
around the single bonds in the
substituents have to be taken
into account.
The calculations show that,
as expected, the diimino deriv-
atives are relatively rigid mole-
cules. Only a few conforma-
tional families are populated
with the diequatorial confor-
Scheme 1. Synthetic route to chiral DACH-linked oligothiophenes DITn and DATn.
mations being more stable
than the diaxial ones by about
2 kcalmolÀ1. Increasing the
Table 1compares the results obtained with the two differ-
ent procedures and shows that microwave (MW) heating re-
size of the arms does not alter the conformational profile of
the system.
The diamino derivatives are much more flexible and sev-
eral different conformations of similar energy are populated.
The diequatorial conformational families are again energeti-
cally favored and, moreover, a strong tendency for the sub-
stituents to adopt a more compact structure was detected.
The different conformational flexibility of the diimines and
diamines is exemplified in Figure 1in which the most stable
calculated conformations of diimine (R,R)-DIT2 and di-
amine (R,R)-DAT2 are compared with the conformations
present in single crystals (see also the X-ray section below).
In both compounds the substituents are diequatorially ori-
ented. Figure 1shows that the conformation of the diimino
compound that largely prevails in the calculated gas phase
structure is very similar to the conformation present in the
single-crystal X-ray structure. In contrast, the most stable
Table 1. Comparison between microwave irradiation and conventional
heating in the synthesis of diimines 3a–d.
Entry
3
MW heating[a]
Time [min] Yield [%]
Conventional heating[b]
Time [h]
Yield [%]
1
2
3
4
3a
3b
3c
3d
20
20
30
30
9124
70
7124
48
85
24
70
61
55
48[c]
[a] All reactions were carried out in monochlorobenzene at 1008C.
[b] RT in CH2Cl2. [c] In CH2Cl2 under reflux.
duces the reaction time from hours to minutes. This is par-
ticularly advantageous with longer oligothienyl systems,
which need prolonged reaction times for complete conver-
sion. A further advantage of
the MW-assisted procedure
comes from the fact that the
desired products are obtained
in high purity simply by filtra-
tion.
The diamino derivatives
DATn were prepared by re-
duction of the corresponding
DITn using common hydride
sources as previously descri-
bed.[12] With thiophene and bi-
thiophene diimine derivatives,
Figure 1. a) Crystallographic and b) calculated conformations of (R,R)-DAT2 and (R,R)-DIT2.
7306
www.chemeurj.org
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2006, 12, 7304 – 7312

Chiral DACH-Linked Oligothiophenes
FULL PAPER
conformation of the diamino derivative in the gas phase,
which is only slightly more populated than other geometri-
cally similar conformations, differs considerably from that
detected in the single crystal owing to packing interactions.
Films of all these compounds on glass were prepared by
casting a solution of a compound in chloroform (50 mL, c
ꢀ10À3 m) and the corresponding CD spectra were recorded
and compared with the solution spectra to provide informa-
tion about changes in the conformational chirality in differ-
ent phases.
The CD spectra of the cast films of (R,R)-DITn (3a–c)
showed no difference in shape with respect to those in solu-
tion (see the Supporting Information). The quarterthio-
phene derivative 3d, being scarcely soluble in organic sol-
vents, gave nonhomogeneous cast films. In this case, nonrep-
roducible spectra were recorded.
Chiroptical properties: In Figure 2 the UV/Vis and circular
dichroism spectra of the diimines (R,R)-3a–d and diamines
Concerning the diamine derivatives, it was found that in
the case of the (R,R)-diaminobithiophene 4b the Cotton
effect was opposite in sign to that in solution and showed an
increased CD intensity over time, while for the diaminoter-
thiophene 4c (DAT3) the Cotton effect had the same sign in
solution as in the film and a markedly greater CD intensity
was observed in the film spectrum (see the Supporting Infor-
mation).
Figure 3 shows the CD spectra of diimine (R,R)-DIT2
(Figure 3a) in cast film and compares the CD spectra of dia-
mine (R,R)-DAT2 in solution and in cast film (Figure 3b).
In solution, (R,R)-DIT2 (Figure 2a) shows a bisignated
Cotton effect with a negative Davydov component near l=
360 nm (De=À100.65, chirality factor g=À0.0037) and a
positive component near l=324 nm (De=+59.92, g=
+0.0025). The corresponding CD spectrum of the cast film
was identical to that in solution with the negative and posi-
tive components at l=366 (DOD=À0.024, g=À0.025) and
324 nm (DOD=++0.014, g=+0.011), respectively. The spec-
trum did not vary over time, as observed for the other di-
imine derivatives.
Figure 2. UV/Vis and CD spectra of diimines a) (R,R)-3a–d and b) dia-
mines (R,R)-4b,c in chloroform. No appreciable CD signal was measured
for (R,R)-4a.
(R,R)-4b,c in chloroform are reported. The values of maxi-
mum wavelength absorption (lmax), molar absorbance (e),
G
molar CD (De) or ellipticity (Y) of the Cotton peaks, and
the chirality factor (g) for compounds 3a–d and 4a–c both
in solution and as solid films are reported in the Supporting
Information.
In contrast, (R,R)-DAT2 in chloroform shows a bisignated
CD spectrum with a positive component near l=328 nm
(De=+3.96, g=+1.93”10À4) and a negative component
near l=290 nm (De=À1.55, g=À9.06”10À5) (overall P he-
licity). On going from solution to film, DAT2 shows inver-
sion of the Cotton effect with a negative component near
l=340 nm (DOD=À0.0017, g=À0.0036) and a positive
component near l=290 nm (DOD=+0.00072, g=+0.0014)
indicating an overall negative chirality (M helicity). Thus,
during the transition of DAT2 from solution to the solid
state an inversion in relative orientations of the two chro-
mophoric groups, corresponding to a helicity inversion,
takes place.
The wavelengths of maximum absorption for DITn in-
crease with the size of the oligothiophene arms as a result of
the higher degree of delocalization in longer conjugated
thienyl chains. As shown in Figure 2, the CD spectra of
DITn are characterized by a strong bisignated Cotton effect.
According to the exciton coupling theory of Nakanishi and
co-workers, the overall negative chirality observed for
(R,R)-DITn derives from the relative orientation and inter-
action of the two oligothiophene arms which are arranged in
an M helical conformation (M helicity).[14]
Relative to the diimine precursors, the CD spectra of the
diamines (R,R)-DATn 4b,c in chloroform showed much
weaker bisignated Cotton effects and had an overall positive
sign (P helicity, Figure 2). Also in these compounds the
maximum wavelength absorption, corresponding to the
crossover of the exciton couplet, was red-shifted on increas-
ing the size of the oligothiophenes.
Figure 3c shows the film spectra of (R,R)- and (S,S)-
DAT2. As expected, the spectra show that the two com-
pounds are enantiomeric. The fact that they show exactly
the same profile, allows the presence of artefacts in the
spectra to be excluded.[15]
Single-crystal X-ray structures of diimine DIT2 and diamine
DAT2: (R,R)-Diimine DIT2 (3b) and (R,R)-diamine DAT2
(4b) yielded crystals suitable for X-ray diffraction studies.
Figure 1shows the single-crystal conformation of both com-
pounds together with the corresponding preferred confor-
In marked contrast to the corresponding diimine 3a, no
CD signal was measured for the monothiophene diamine 4a
in the range of 240–500 nm.
Chem. Eur. J. 2006, 12, 7304 – 7312
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
7307

M. Melucci et al.
DAT2 was the only compound that gave highly crystalline
cast films. For this compound it was possible to follow the
film growth by joint optical microscopy, atomic force mi-
croscopy, and X-ray diffraction.
Optical microscopy displayed fast nucleation followed by
growth with dendritic modalities resulting in triangular-
shaped crystals over the entire substrate surface that exhibit-
ed birefringence. Figure 4 shows the polarized optical micro-
Figure 3. a) UV/Vis and CD spectra of (R,R)-DIT2 (3b) in cast film.
b) UV/Vis and CD spectra of (R,R)-DAT2 (4b) in chloroform (dashed
line) and in cast film (black line) and evolution over time of the CD am-
plitude in the cast film (t=10, 30, 60 min; 3, 4 h). c) Comparison of the
CD spectra of films of (R,R)- and (S,S)-DAT2 (4b). The ellipticity nor-
malized for thickness and expressed in mdegnmÀ1 is reported for spectra
(a) and (c).
Figure 4. Optical micrographs with crossed polars of DAT2 film forma-
tion. The films were prepared by drop-casting on glass from 0.5 mm solu-
tions in CHCl3. The yellow arrows in the first row show the orientation
of the crossed polars. The left column shows the evolution of enantiopure
diamine (R,R)-DAT2, the right column the evolution of racemic DAT2.
mations calculated for the gas phase.[16] In (R,R)-DIT2 (3b)
the two bithiophene arms, which lie in the same plane as the
imino groups, are perpendicular to each other and oriented
in opposite directions. In contrast, the bithiophene arms of
(R,R)-DAT2 (4b) approximately face each other so that the
molecule assumes the shape of a small helicene. The X-ray
structure of DAT2 reveals the presence of an intramolecular
scopy images of the film growth of (R,R)-DAT2 (4b). For
comparison, we also studied the behavior of the racemic
mixture of DAT2 (racemic DAT2) for which crystallization
was markedly slower (a few hours vs a few minutes). In this
case the crystallization resulted in the deposition of needle-
shaped crystals of 100 mm length (Figure 4).[7b,18] After crys-
tallization, the morphology becomes stable and does not
change with the aging of the sample.
The AFM images of enantiopure DAT2 (4b) films were
consistent with optical microscopy observations as they
showed the formation of an amorphous and very smooth
film immediately after preparation evolving into a crystal-
line film within a few minutes (Figure 5). After complete
crystallization of 4b, crystals of dimensions ranging from mi-
crometers to millimeters were observed in the film. They
showed typical terrace structures with very flat terraces (rms
roughness <1nm), the smallest step being of about 1.5 nm.
Moreover some helicoidal structures (helicoids) with micro-
À
S···H N interaction involving one inner sulfur atom and the
amino hydrogen of the opposite pendant, as depicted in
Figure 1.[17] Moreover, the crystal packing shows “slipped”
p–p intermolecular stacking interactions along the c axis be-
tween thiophene rings of adjacent ribbons running along the
b axis, which probably induces a lower crystal packing
energy.
Thin-film characterization: The morphology of the diimine
and diamine cast films was investigated by polarized optical
microscopy and atomic force microscopy (AFM). Drop cast
films of DIT1, DIT2, and DAT1 (both enantiomers) from
chloroform were completely amorphous and smooth (root
mean square (rms) roughness <1nm). Also, no sign of
order was detected in cast films of DIT3, DAT3, and DIT4.
7308
www.chemeurj.org
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2006, 12, 7304 – 7312

Chiral DACH-Linked Oligothiophenes
FULL PAPER
structure of (R,R)-DAT2 with the a,b planes (00l) in contact
G
with the glass surface are proposed in Figure 6.
Discussion
Our data show that the use of DACH scaffolds is a valuable
way to obtain helical oligothiophene-based compounds with
controllable helicity in solution. The helixlike conformation
is maintained on increasing the size of the oligothiophene,
indicating that DACH strongly acts to constrain the overall
molecular structure. Switching of the helicity is achieved by
changing the type of linker. For instance, the M helicity of
diimines with R,R configuration turns to P helicity for di-
amines with the same absolute configuration, in accord with
observations by Kwit and Gawronski for other diaryl-
DACH derivatives.[11]
In solution, the intensity of the Cotton effect observed for
diimines was significantly greater than that of the corre-
sponding diamines. This effect can be rationalized through
theoretical calculations which show that the C=N double
bonds in diimine derivatives lead to conformational rigidity
and to a highly preferred conformation, while in the diamine
derivatives there are several geometrically different but
almost isoenergetic conformations. In agreement with this,
for diimine DIT2 the calculated structure is almost identical
to that present in the single crystal, while in the case of dia-
mine DAT2 the most stable conformation differs considera-
bly from that detected in the crystal. In cast films the CD
spectra of the diimine derivatives are similar to those ob-
served in solution. Again, this result can be accounted for
by the conformational rigidity of DITn.
Figure 5. Evolution of the morphology of a cast film of diamine (R,R)-
DAT2 (4b) on glass. The Z scale is 0–40 nm. a) Film morphology just
after film preparation. b) Image acquired during the crystallization proc-
ess. c) Detailed image of two helicoids formed during film crystallization.
No influence of the AFM tip was observed in the morphology of crystal-
lizing films.
metric dimensions were observed on the surface (Figure 5).
The helicoids were formed during crystallization and optical
microscopy showed birefringence, however, no extinguish-
ment effects were observed by rotating the polars (on the
contrary, the crystallites displayed some extinguishment ac-
cording to optical anisotropic behavior of DAT2 crystals).
Although the helicoids seem to exhibit chirality (both
left- and right-handed), no relationship with molecular chir-
ality was observed.
The X-ray diffraction patterns of enantiopure and racemic
DAT2 films (Figure 6) exhibited identical interplanar distan-
ces as well as molecular packing, indicating that chiral reso-
lution of the racemate into homochiral crystals had taken
place.[8c] Figure 6 shows the X-ray diffraction plots of enan-
tiopure (R,R)- and racemic DAT2, together with the calcu-
lated X-ray diffraction profile of the former obtained by as-
suming a strongly preferred orientation of the 00l planes
parallel to the substrate. The strong similarity between the
experimental and calculated plots confirms that such an ori-
entation is present in all samples. Some sketches of the
The CD signal from thin films of the more flexible diami-
no derivatives is remarkably more intense than that ob-
served in solution.
The behavior of the enantio-
pure (R,R)- and (S,S)-diamino-
bis(bithiophenes) is unique,
since for these compounds we
observed the crystalline growth
of the film, CD inversion, and
chiral amplification on passing
from solution to solid film.
In enantiopure DAT2 the
helicity inversion from P to M
helicity for the R,R configura-
tion (or from M to P helicity
for the S,S configuration) can
be explained by assuming that
(R,R)-4b exists in solution as
an equilibrium of different
conformational isomers with a
Figure 6. Left: XRD profile of racemic and enantiopure DAT2 drop cast films from chloroform. a) Racemic
DAT2, b) (S,S)-DAT2, c) (R,R)-DAT2 calculated from the preferred orientation, and d) (R,R)-DAT2. The
Miller indexes of the calculated peaks are reported. Right (bottom): Sketches of the organization of (R,R)-
DAT2 molecules on a glass substrate. Two of the possible arrangements of the crystals are shown: the a,b
plane is parallel to the substrate. Right (top): Crystalline film and possible arrangement of the crystallographic
axes in the different domains.
slight preference for those with
P helicity. Passing from solu-
tion to the solid film, a confor-
mational change takes place
leading to an M helical form,
Chem. Eur. J. 2006, 12, 7304 – 7312
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
7309

M. Melucci et al.
which is stabilized by the intramolecular S···H interaction
between the sulfur atom of one arm and the hydrogen atom
On the basis of the experimental evidence presented here,
it can be concluded that the peculiar behavior of enantio-
meric pure diaminobis(bithiophene) can be rationalized in
terms of conformational flexibility and a subtle interplay of
intra- as well as intermolecular nonbonding interactions
(i.e., hydrogen bonding, p stacking) involving both the
chiral backbone and the oligothienyl pendants.
In contrast to DAT2, the shape of the CD spectrum of the
cast film of the bis-terthiophene derivative DAT3 (4c) is
very similar to that in solution, but is much more intense.
For this compound it is likely that, despite the highly mobile
À
of the N H group of the opposite arm, as highlighted by
single-crystal X-ray data. In turn, this conformational
change is promoted by the minimization of the crystalline
À
packing energy in the film. Note that intramolecular S···H
N hydrogen bonds have so far been reported only for thia-
porphyrin systems[19] in which an appropriate orientation of
atoms is imposed by the molecular geometry.
A working mechanism for helicity inversion in (R,R)-
DAT2 is illustrated in Figure 7. During the transition from
solution to amorphous solid to crystalline film, the P helical
(R,R)-DAT2 conformers, which are slightly dominant in so-
lution and in the solid amorphous phase, are progressively
converted into the M helical conformers by rotation of the
À
C N single-bond linker, the increased size of the pendants
makes molecular rearrangements more difficult. However,
the enhanced CD intensity observed for the cast films indi-
cates that one preferred conformation exists in films.
À
C N bond of one arm.
The chiral amplification observed during film formation
(see Figure 3b) can be ascribed to the increasing number of
molecules characterized by M helicity with respect to those
with P helicity during the 24 h required for complete film
crystallization.
The kinetics for the growth of the cast film of racemic
DAT2 are different to those of the enantiopure compounds,
as shown in Figure 4, indicating that a chiral self-recognition
process takes place between molecules with the same con-
figuration. The occurrence of this chiral discrimination pro-
cess is in agreement with the results obtained by X-ray dif-
fraction of the films. Figure 6 shows that the same pattern is
found for enantiopure and racemic compounds, confirming
the deposition of homochiral crystals during the crystalliza-
tion of the racemic form, as observed for many chiral conju-
gated molecules on solid surfaces.[8c]
Conclusion
In summary, we have presented new chiral helix-shaped oli-
gothiophenes and demonstrated how the stereochemistry of
DACH, the size of the side arms, and the type of DACH-oli-
gothiophene linkers determine the conformational flexibility
of these compounds and hence the overall handedness in
solution and in solid film. In cast films these parameters are
strictly related to supramolecular organization.
We have also demonstrated the detailed mechanism and
the driving forces that in enantiopure diaminobis(bithio-
phene) DAT2 leads to the transfer of chirality from the mo-
lecular level in solution to the supramolecular level in film
with inverted chirality. The peculiar case of this compound
shows that noncovalent interactions in the solid state are
crucial in determining thin-film properties. Such interactions,
which play a major role in bio-
logical and supramolecular
chemistry, should also be taken
into account when designing
new molecular materials for
optical and electrical applica-
tions.
Experimental Section
General: Microwave-assisted reac-
tions were carried out in air using a
commercial system, Synthewave 402
(Prolabo), with variable power and at
a fixed temperature. Analytical thin-
layer chromatography (TLC) was car-
ried out by using 0.2 mm sheets of
silica gel 60 F254 and visualization was
accomplished with UV light (356 and
254 nm). UV/Vis and CD spectra
were recorded with a JASCO J-810
spectropolarimeter under ambient
Figure 7. a) Schematic representation of the mechanism of helicity inversion for (R,R)-DAT2 (4b) from solu-
conditions. A Nikon Eclipse 80i opti-
cal microscope was used for optical
measurements. The images were re-
À
tion to thin film ascribable to a N C bond rotation. b) Sketch of the bulk state transition for (R,R)-DAT2
from the amorphous to the crystalline phase.
7310
www.chemeurj.org
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2006, 12, 7304 – 7312

Chiral DACH-Linked Oligothiophenes
FULL PAPER
corded with a Nikon Coolpix 5400 digital color camera. Glass substrates
were furnished by Knittel gläser and were washed with spectroscopic
grade acetone (Aldrich) prior to use. Spectroscopic grade CHCl3 (Al-
drich) was used in solution preparation. Calculations were carried out by
utilizing the HyperChem software package.[20] Melting points were deter-
mined by a Buchi-B540 and are uncorrected. IR analysis were performed
with a FT-IR NICOLET 205 spectrophotometer and the spectra are ex-
pressed by wavenumber (cmÀ1). Elemental analyses were carried out by
using a EACE 1110 CHNOS analyzer. 1H NMR and 13C NMR spectra
were recorded on a VARIAN-Mercury 400MHz spectrometer. Films
were cast from a chloroform solution (~50 mL, c~10À3 m) on glass sub-
strates and the solvent was evaporated under saturated atmosphere.
filtration the solvent was evaporated and the solid was washed with
warm isopropanol to gave DIT3 as a yellow solid (135 mg, 70%). M.p.
1
1468C; [a]D =À830 (c=1.01 in CHCl3); H NMR (CDCl3, 400 MHz): d=
1.43 (brs, 4H), 1.85 (brs, 4H), 3.37 (brs, 2H), 7.01–7.23 (m, 14H),
8.21ppm (s, 2H); 13C NMR (CDCl3, 100 MHz): d=24.4, 32.8, 73.4, 123.4,
123.9, 124.4, 124.7, 125.0, 127.9, 131.0, 135.9, 136.9, 137.0, 139.5, 140.9,
154.1 ppm; IR (Nujol): n˜ =2853, 2726, 1623, 1461, 1377, 792 cmÀ1; UV/
Vis (CH2Cl2): labs =390, lem =477 nm; EI-MS: m/z: 149 (10), 275 (100),
357 (28), 382 (21), 630 (11) [M +]; elemental analysis calcd for C32H26N2S6
C
(630.04): C 60.91, H 4.15, N 4.44; found: C 60.85, H 4.12, N 4.42.
(1R,2R)-N,N’-Bis(5’’’-hexyl-2,2’:5’,2’’:5’’,2’’’-quarterthiophen-5-ylmethyle-
ne)cyclohexane-1,2-diamine, DIT4 (3d): Aldehyde 2d (500 mg,
1.13 mmol) and diamine 1 (65 mg, 0.57 mmol) were dissolved in mono-
chlorobenzene (15 mL) and introduced into a microwave oven reactor.
The mixture was irradiated for 40 min at 1008C and then cooled to room
temperature. The precipitate formed was filtered and then washed with
warm n-hexane affording diimine 9 (350 mg, 64%) as an orange powder.
M.p. 1938C; [a]D =À1895 (c=0.2 in CH2Cl2); 1H NMR (CDCl3,
400 MHz): d=0.90 (brs, 6H), 1.61 (m, 24H), 2.80 (m, 4H), 3.20 (brs,
2H), 6.69 (s, 2H), 7.04 (m, 14H), 8.22 ppm (s, 2H); 13C NMR (CDCl3,
100 MHz): d=14.0, 22.6, 24.4, 28.7, 30.2, 31.5, 32.8, 73.41, 123.5, 124.1,
124.5, 124.9, 125.1, 131.2, 134.3, 134.9, 135.7, 136.9, 137.2, 139.5, 145.8,
154.1 ppm; IR (Nujol): n˜ =2852, 2780, 1623, 1460, 1377, 791 cmÀ1; UV/
Vis (CH2Cl2): labs =420, lem =510 nm; EI-MS: (m/z): 441, 482; elemental
analysis calcd for C52H54N2S8 (963.21): C 64.82, H 5.65, N 2.91; found: C
64.78, H 5.60, N 2.90.
Crystal data were collected on a Bruker AXS CCD diffractometer (MoKa
radiation, l=0.71073 Š). Empirical absorption correction was applied,
initial structure model by direct methods, and anisotropic full-matrix
least-squares refinement on F2.
XRD measurements were carried out at room temperature with a Bragg/
Brentano diffractometer (XꢂpertPro Panalytical) equipped with a graph-
ite monochromator in the diffracted beam and by using a copper anode
as the X-ray source. The simulated X-ray diffraction pattern was ob-
tained by using the PowderCell program.[21]
Materials: 2,2’-Bithiophenyl-5-carbaldehyde (2b), enantiomerically pure
(1R,2R)-1,2-diaminocyclohexane (1), and monochlorobenzene were ob-
tained from Aldrich and used without further purification. The synthesis
and characterization of aldehyde 2c and diamines 4a–c have already
been described.[12a] 5’’’-Hexyl-2,2’:5’,2’’:5’’,2’’’-quarterthiophene-5-carbalde-
hyde (2d) was synthesized following a known procedure.[22]
(1R,2R)-N,N’-Bis(thiophen-2-ylmethylene)cyclohexane-1,2-diamine,
DIT1 (3a): The microwave oven reactor was charged with thiophene-2-
carbaldehyde (2a) (200 mg, 1.77 mmol), (1R,2R)-1 (100 mg, 0.89 mmol),
MgSO4 (150 mg), and monochlorobenzene (1.5 mL). The mixture was ir-
radiated for 10 min at 1008C then further compound 1 (50 mg) was
added and the mixture was irradiated for an additional 10 min at 1008C.
The MgSO4 was filtered off and the solvent evaporated. The solid ob-
tained was crystallized from n-hexane to gave DIT1as a white solid
(240 mg, 91%). M.p. 120 8C; [a]D =À23.6 (c=0.64 in CHCl3); 1H NMR
(CDCl3, 400 MHz): d=1.44–1.50 (m, 2H), 1.78–1.85 (m, 6H), 3.30–3.33
(m, 2H), 6.96 (dd, J=3.6, 4.8 Hz, 2H), 7.14 (d, J=4.0 Hz, 2H), 7.29 (d,
J=4.8 Hz, 2H), 8.27 ppm (s, 2H); 13C NMR (CDCl3, 100 MHz): d=24.4,
32.8, 73.4, 94.5, 127.2, 128.2, 130.2, 154.4 ppm; IR (Nujol): n˜ =3383, 3073,
2922, 2853, 1630, 1460, 1432, 1377, 1087, 716 cmÀ1; UV/Vis (CH2Cl2):
labs =278, lem =420 nm; EI-MS: m/z: 112 (32), 160 (24), 193 (100), 302
Acknowledgements
This work was supported by projects EU-NMP-IP 500355 NAIMO,
Marie Curie RTN CHEXTAN and FIRB RBNE03S7XZ_005. Thanks
are due to Dr. Maria Antonietta Loi (Istituto per lo Studio dei Materiali
Nanostrutturati ISMN-Sez Bo, CNR, Italy) for the optical and fluores-
cence microscopy images of enantiopure and racemic DAT2 4b.
[1] G. Barbarella, M. Melucci, G. Sotgiu, Adv. Mater. 2005, 17, 1581–
1593.
[2] a) H. Sirringhaus, Adv. Mater. 2005, 17, 2411–2425; b) G. Witte, C.
Wçll, J. Mater. Res. 2004, 19, 1889–1916; c) C. D. Dimitrakopoulos,
P. R. L. Malenfant, Adv. Mater. 2002, 14, 99–117; d) H. Hoppe, N. S.
Sariciftci, J. Mater. Res. 2004, 19, 1924–1945; e) A. Kçler, J. S. R.
Wilson, H. Friend, Adv. Mater. 2002, 14, 701–707.
(15) [M +]; elemental analysis calcd for C16H18N2S2 (302.09): C 63.54, H
C
6.00, N 9.26; found: C 63.52, H 5.96, N 9.23.
ACHTREUNG
ACHTREUNG
[3] F. Dinelli, M. Murgia, F. Biscarini, D. M. De Leeuw, Synth. Met.
2004, 146, 373–376.
[4] R. Garcia, M. Tello, Nano Lett. 2004, 4, 1115–1119.
[5] G. Derue, S. Copp›e, S. Gabriele, M. Surin, V. Geskin, F. Monte-
verde, P. Lecl›re, R. Lazzaroni, P. Damman, J. Am. Chem. Soc.
2005, 127, 8018–8019.
[6] F. Dinelli, M. Murgia, P. Levy, M. Cavallini, F. Biscarini, D. M.
De Leeuw, Phys. Rev. Lett. 2004, 92, 116802-1.
[7] a) A. T. ten Cate, P. Y. W. Dankers, H. Kooijman, A. L. Spek, R. P.
Sijbesma, E. W. Meijer, J. Am. Chem. Soc. 2003, 125, 6860–6861;
b) A. P. H. J. Schenning, A. F. M. Kilbinger, F. Biscarini, M. Cavalli-
ni, H. J. Cooper, P. J. Derrick, M. J. Feast, R. Lazzaroni, Ph. Lecl›re,
L. A. McDonell, E. W. Meijer, S. C. J. Meskers, J. Am. Chem. Soc.
2002, 124, 1269–1275; c) D. Beljonne, B. M. W. Langeveld-Voss, Z.
Shuai, R. A. J. Janssen, S. C. J. Mekers, E. W. Meijer, J. L. Bredas,
Synth. Met. 1999, 912–913.
[8] a) A. Miura, P. Jonkeijm, S. De Feyter, A. P. H. J. Schenning, E. W.
Meijer, F. C. De Schryver Small, 2005, 1, 131–137; b) M. C. Blüm,
E. Æavar, M. Pivetta, F. Patthey, W. D. Schneider, Angew. Chem.
2005, 117, 5468–5471; Angew. Chem. Int. Ed. Engl. 2005, 44, 5334–
5337; c) W. Mamdouh, H. Uji-i, A. E. Dulcey, V. Percec, S. De Feyt-
er, F. C. De Schryver, Langmuir 2004, 20, 7678–7685; d) S. M.
Barlow, S. Louafi, D. Le Roux, J. Williams, C. Muryn, S. Haq, R.
1
(52 mg, 0.46 mmol), MgSO4 (50 mg), and monochlorobenzene (3 mL).
The mixture was irradiated for 10 min then further 1 (26 mg, 0.23 mmol)
was added. The mixture was irradiated for an additional 10 min and then
the MgSO4 was filtered off. After evaporating the solvent, the powder
obtained was crystallized from isopropanol/pentane to gave DIT2 as a
white powder (150 mg, 71%). M.p. 136–1378C; [a]D =À1195 (c=0.9 in
1
CHCl3); H NMR (C6D6, 400 MHz): d=1.20–1.28 (m, 2H), 1.58–1.63 (m,
2H), 1.80 (brs, 4H), 3.22–3.28 (m, 2H), 6.49 (dd, J=3.6, 5.2 Hz, 2H),
6.58–6.60 (m, 4H), 6.68 (d, J=4.0 Hz, 2H), 6.89 (dd, J=0.8, 3.6 Hz, 2H),
8.00 ppm (s, 2H); 13C NMR (C6D6, 100 MHz): d=24.6, 33.2, 73.7, 123.8,
124.5, 125.0, 128.7, 130.8, 137.6, 140.0, 142.0, 153.8 ppm; IR (Nujol): n˜ =
2922, 2854, 1624, 1461, 1377, 791, 696 cmÀ1; UV/Vis (CH2Cl2): labs =345,
lem =447 nm; EI-MS: m/z: 193 (100), 275 (80), 300 (50), 466 (20) [M +];
elemental analysis calcd for (C24H22N2S4) (466.07): C 61.76, H 4.75, N
6.00; found: C 61.80, H 4.72, N 5.98.
C
(1R,2R)-N,N’-Bis(2,2’:5’,2’’-terthiophen-5-ylmethylene)cyclohexane-1,2-
diamine, DIT3 (3c): 2,2’:5’,2’’-Terthiophene-5-carbaldehyde (2c) (170 mg,
0.62 mmol), diamine 1 (36 mg, 0.31mmol), and MgSO 4 (180 mg) were
dissolved in monochlorobenzene (4 mL) and introduced into a micro-
wave oven reactor. After 15 min of irradiation at 1008C further 1 (18 mg)
was added and the mixture was irradiated for an additional 15 min. After
Chem. Eur. J. 2006, 12, 7304 – 7312
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
7311

M. Melucci et al.
Raval, Langmuir 2004, 20, 7171–7176; e) S. De Feyter, A. Ges-
qui›re, K. Wurst, D. S. Amabilino, J. Veciana, F. C. De Schryver,
Angew. Chem. 2001, 113, 3317–3320; Angew. Chem. Int. Ed. 2001,
40, 3217–3220; f) A. Gesqui›re, P. Jonkheijm, F. J. M. Hoeben,
A. P. H. J. Schenning, S. De Feyter, F. C. DeSchryver, E. W. Meijer,
Nano Lett. 2004, 4, 1175–1179; g) M. Miyasaka, A. Rajca, M. Pink,
S. Rajca, Chem. Eur. J. 2004, 10, 6531–6539; h) A. Gesqui›re, M. M.
Abdel-Mottaleb, S. De Feyter, F. C. De Schryver, F. Schoonbeek, J.
van Esch, R. M. Kellogg, B. L. Feringa, A. Calderone, R. Lazzaroni,
J. L. Brꢃdas, Langmuir 2000, 16, 10385–10391.
matrix least-squares refinement on F2. Data for DAT2: C24H26N2S4;
Mr =470.71; orthorhombic P212121; a=9.144(4), b=14.195(7), c=
18.624(9) Š; V=2417(2) Š3; Z=4; Dx =1.293 MgmÀ3
;
m=
0.407 mmÀ1
;
F
ACHTREUNG
flections; 1029 I>2s(I). Final indices: R1 =0.0822, wR2 =0.1419.
GOF=0.848, absolute structure parameter=À0.2(3). Data for
DIT2: C24H22N2S4; Mr =466.68; tetragonal P41212; a=6.2940(4), b=
6.2940(4),
c=58.515(4) Š;
;
V=2318.0(3) Š3;
Z=4;
Dx =
=
1.337 MgmÀ3
m=0.424 mmÀ1
;
F
A
28.018; 21459 reflections; 2473 I>2s(I). Final indices: R1 =0.0714,
wR2 =0.1631. GOF=1.143, absolute structure parameter=0.2(2).
CCDC-275638 (DAT2, 4b) and CCDC-275639 (DIT2, 3b) contain
the supplementary crystallographic data for this paper. These data
can be obtained free of charge from the Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
[9] a) E. L. Eliel, S. H. Wilen, Stereochemistry of Organic Compounds,
Wiley, New York, 1994; b) R. Fasel, M. Parschau, K. H. Ernst,
Nature 2006, 439, 449–452; c) F. J. M. Hoeben, P. Jonkheijm, E. W.
Meijer A. P. H. J. Schenning, Chem. Rev. 2005, 105, 1491–1546;
d) J. J. L. M. Cornelissen, A. E. Rowan, R. J. M. Nolte, N. A. J. M.
Sommerdijk, Chem. Rev. 2001, 101, 4039–4070.
[10] P. Lecl›re, M. Surin, R. Lazzaroni, A. F. M. Kilbinger, O. Henze, P.
Jonkheijm, F. Biscarini, M. Cavallini, W. J. Feast, E. W. Meijer,
A. P. H. J. Schenning, J. Mater. Chem. 2004, 14, 1959–1963.
[11] M. Kwit, J. Gawronski, Tetrahedron 2003, 59, 9323–9331.
[12] a) V. G. Albano, M. Bandini, M. Melucci, M. Monari, F. Piccinelli, S.
Tommasi, A. Umani-Ronchi, Adv. Synth. Catal. 2005, 347, 1507–
1512; b) V. G. Albano, M. Bandini, G. Barbarella, M. Melucci, M.
Monari, F. Piccinelli, S. Tommasi, A. Umani-Ronchi, Chem. Eur. J.
2006, 12, 667–676.
[17] F. A. Hallen, C. M. Bird, R. S. Rowland, P. R. Raithby, Acta Crystal-
logr., Sect. B 1997, 53, 680–695.
[18] B. M. W. Langeveld-Voss, D. Beljonne, Z. Shuai, R. A. J. Janssen,
S. C. J. Meskers, E. W. Meijer, J.-L. Brꢃdas, Adv. Mater. 1998, 10,
1343–1348.
[19] a) S. J. Narayanan, B. Sridevi, T. K. Chandrashekar, A. Vij, R. Roy,
J. Am. Chem. Soc. 1999, 121, 9053–9068; b) S. J. Narayanan, B. Sri-
devi, T. K. Chandrashekar, A. Vij, R. Roy, Angew. Chem. 1998, 110,
3582–3585; Angew. Chem. Int. Ed. 1998, 37, 3394–3397; c) N. Agar-
wal, C.-H. Hung, M. Ravikanth, Eur. J. Org. Chem. 2003, 3730–
3734; d) V. G. Anand, S. K. Pushpan, S. Venkatraman, A. Dey, T. K.
Chandrashekar, B. S. Joshi, R. Roy, W. Teng, K. R. Senge, J. Am.
Chem. Soc. 2001, 123, 8620–8621.
[20] HyperChem rel. 7.0, Windows Molecular Modeling System, Hyper-
Cube, Inc and Autodesk Inc, developed by HyperCube, Waterloo,
Ontario, Canada, 1993.
[21] PowderCell for Windows, W. Kraus, G. Nolze, Federal Institute for
Materials and Testing (BAM), Berlin, Germany, version 2.3, 1999.
[22] M. Melucci, G. Barbarella, M. Zambianchi, M. Benzi, F. Biscarini,
M. Cavallini, A. Bongini, S. Fabbroni, M. Mazzeo, M. Anni, G.
Gigli, Macromolecules 2004, 37, 5692–5702.
[13] J. J. P. Stewart, J. Comput. Chem. 1989, 10, 209–220.
[14] a) N. Harada, K. Nakanishi, Circular Dichroic Spectroscopy: Exciton
Coupling in Organic Stereochemistry, University Science Books, Mill
Valley, CA, 1983; b) N. Ikemoto, I. Estevez, K. Nakanishi, N.
Berova, Heterocycles 1997, 46, 489–501.
[15] Artefacts due to linear dichroism can be excluded by considering
the LD low values measured (ꢀ10À3). The spectra were also repro-
ducible after substrate rotation. Circular Dichroism (Eds.: N.
Berova, K. Nakanishi, R. W. Woody), Wiley, New York, 2000,
p. 159.
[16] Crystal data were collected on a Bruker AXS CCD diffractometer
(MoKa radiation, l=0.71073 Š): Empirical absorption correction ap-
plied, initial structure model by direct methods and anisotropic full-
Received: March 6, 2006
7312
www.chemeurj.org
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2006, 12, 7304 – 7312