Click Chemistry Derived Pyridazines: Electron-Deficient Building Blocks with Defined Conformation and Packing Structure

Article abstract of DOI:10.1002/asia.201701277

A series of 3,6-bis(4-triazolyl)pyridazines equipped with terminal phenyl substituents with varying degree of fluorination were synthesized by using the facile copper-catalyzed azide–alkyne cycloaddition and their structures were thoroughly investigated i

Full text of DOI:10.1002/asia.201701277

CHEMISTRY
AN ASIAN JOURNAL
www.chemasianj.org
Accepted Article
Title: Click Chemistry Derived Pyridazines: Electron-Deficient Building
Blocks with Defined Conformation and Packing Structure
Authors: Irén Birkenfelder, Johannes Gurke, Lutz Grubert, Stefan
Hecht, and Bernd M. Schmidt
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Asian J. 10.1002/asia.201701277
Link to VoR: http://dx.doi.org/10.1002/asia.201701277
A Journal of
A sister journal of Angewandte Chemie
and Chemistry – A European Journal

10.1002/asia.201701277
Chemistry - An Asian Journal
FULL PAPER
Click Chemistry Derived Pyridazines: Electron-Deficient Building
Blocks with Defined Conformation and Packing Structure
Irén Birkenfelder,[a] Johannes Gurke,[a] Lutz Grubert,[a] Stefan Hecht,*[a] and Bernd M. Schmidt*[a]
Abstract: A series of 3,6-bis(4-triazolyl)pyridazines equipped with
terminal phenyl substituents with varying degree of fluorination were
synthesized by the facile copper-catalyzed azide-alkyne
cycloaddition and their structures were thoroughly investigated in the
gas phase, in solution, and in the solid state by employing DFT
calculations, NMR spectroscopy, and single-crystal X-ray diffraction,
respectively. On the molecular level, their structure is governed by
the strong preference of the triazole-pyridazine linkages for the anti-
conformation. The molecules' supramolecular organization in the
crystalline solid is controlled by -stacking, C-H··· as well as
C-F···H interactions. The latter can conveniently be tuned by the
number and position of fluorine substituents in the terminal phenyl
units, giving rise to either herringbone-like, 1D or 2D lamellar
packing. Electrochemistry and optical spectroscopy of all
compounds suggest that they might find use as electron-transporting
/ hole-blocking materials in organic electronics.
connecting the triazolyl and (het)aryl units as illustrated for the
case of 2,6-bis(1-aryl-1,2,3-triazol-4-yl)pyridines (BTPs) in
Scheme 1, left.[9] However, in these designs the generated kinks
are substantial and lead to helical foldamers with limited
diameter and hence little potential for binding of larger organic
guests in their interior.[10] Thus, we became interested in
extended motifs with more subtle curvature in order to construct
helices with larger inner diameter. Utilizing the same attractive
two-fold H-bonding interactions between the acidic triazole H-
atom and the neighboring ortho-N-atom as well as the ortho-H-
atom and the triazole-N(3)-atom - and thereby avoiding the
strongly repulsive N-N-interactions in the disfavored syn,syn-
conformation - we introduced a central pyridazine unit to
generate 3,6-bis(4-triazolyl)pyridazines (BTPNs, see Scheme 1,
right).[11] The BTPNs should display a much wider angle and in
addition, due to their large extent of nitrogen incorporation,
exhibit strong electron-accepting properties, potentially
interesting for electron-transporting/hole-blocking materials.
Introduction
R
The Cu-catalyzed azide-alkyne cycloaddition reaction (CuAAC)[1]
with its oftentimes virtually quantitative yields and exclusive
regioselectivity when compared to the uncatalyzed 1,3-dipolar
cycloaddition as pioneered by Huisgen[2] quickly advanced to
one of the most useful reactions available. This specific
transformation's exceptional utility is documented by the fact that
despite its rather recent discovery it has been employed across
fields, including bioorganic chemistry,[3a,b] organic[3c] and material
synthesis[3d] as well as polymer science[3e] and supramolecular
chemistry.[3f,g] The generated 1,2,3-triazole ring is furthermore a
suitable ligand in organometallic coordination chemistry[3h] and
has attracted considerable attention in homogeneous catalysis.[4]
Even in the absence of coordinating metal ions, triazole-
containing building blocks are able to display well-defined
conformational preferences,[4] which can be used to replace
amide bonds in peptidomimetics,[5] or to design (hetero)aromatic
foldamers.[6] For the latter, we were originally interested in
triazole-derived motifs with defined kinks and explored in
particular pyridine[7] but also properly ortho-substituted phenyl
moieties.[8] In these designs, we took advantage of the high
preference for the anti,anti-conformation about the C-C bond
N
N
N
N
N
N
N
N
N
N
N
N
N
R
R
N
N
R
R
BTPN
BTP
increasing substituent distance from BTP to BTPN
Scheme 1. Triazole-containing kinked structural motifs 2,6-bis(1-aryl-1,2,3-
triazol-4-yl)pyridine (BTP) and 3,6-bis(4-triazolyl)pyridazines (BTPN) in their
predominantly populated anti,anti-conformation.
Herein we present a systematic investigation of BTPNs, in
particular focusing on a series of fluorinated derivatives to
further increase their acceptor strength and modulate their
packing behavior. We studied their structure on the molecular
level with regard to backbone conformation, both in solution as
well as in the crystalline solid and compared our experimental
with computational results. With the aid of single-crystal X-ray
diffraction, we were able to decipher packing interactions, which
are critical for the compounds' electronic properties in the bulk.
In addition, we investigated their optoelectronic properties, i.e.
their ability to act as suitable electron-acceptors while
maintaining their optical gap and remaining transparent in the
visible region of the spectrum.
[a]
Irén Birkenfelder, Johannes Gurke, Dr. Lutz Grubert, Prof. Stefan
Hecht, Dr. Bernd M. Schmidt
Department of Chemistry and IRIS Adlershof, Humboldt-Universität
zu Berlin, Brook-Taylor-Str. 2, 12489 Berlin, Germany
Email: sh@chemie.hu-berlin.de; bernd.schmidt@hu-berlin.de
Supporting information for this article is given via a link at the end of
the document.
For internal use, please do not delete. Submitted_Manuscript
This article is protected by copyright. All rights reserved.

10.1002/asia.201701277
Chemistry - An Asian Journal
FULL PAPER
N
N
R5
R5
N
N
N
N
10 mol% CuSO4
20 mol% Na ascorbate
10 mol% TBTA
R4
R3
R4
R3
N
N
Results and Discussion
N N
R1
1
R1
R2
R2
+
To maximize the modularity of the system, 3,6-ethynylpyridazine
(1) was envisioned to be coupled with the respective azides
(2a-h) by employing CuAAC to yield the desired functionalized
H2O/tBuOH/CH2Cl2
RT
3a R1 = R2 = R3 = R4 = R5 = H (67 %)
R5 R4
3b R1
=
; R2 = R3 = R4 = R5 = H (70 %)
F
N3
R3
3c R2 = F; R1 = R3 = R4 = R5 = H (88 %)
3d R3
=
; R1 = R2 = R4 = R5 = H (94 %)
F
R1 R2
3,6-bis(1-aryl-1H-1,2,3-triazol-4-yl)pyridazines
(3a-h).
The
3e R1 = R5 = F; R1 = R3 = R4 = H (39 %)
2a-h
selected core unit 1 was synthesized starting from commercially
available 3,6-dichloropyridazine by Pd-catalyzed ethynylation,[12]
giving the protected 3,6-bisethynylpyridazine (4) in high yield.
Deprotection of tri(iso-propyl)silyl-protected 4 was quantitative
but due to the high reactivity of the building block, it was used
immediately in the subsequent reactions and never stored.
While azides 2a-g can conveniently be synthesized by standard
diazotization,[13] pentafluorophenylazide 2h tends to form
explosive polyazides upon diazotization.[14] Because of their
volatility, prepared azides were not dried excessively but used in
slight excess while still containing residual solvent.
3f R2 = R4 = F; R1 = R3 = R5 = H (41 %)
3g R1 = R2 = R3
=
; R4 = R5 = H (26 %)
F
3h R1 = R2 = R3 = R4 = R5 = F (30 %)
Scheme 2. Synthesis of 3,6-bis(1-aryl-1H-1,2,3-triazol-4-yl)pyridazines 3a-h
by CuAAC (TBTA = tris(benzyltriazolylmethyl)amine). Yields are calculated
based on the conversion of 3,6-ethynylpyridazine 1.
To confirm these conformational preferences for the BTPN
series, solution NMR studies using the nuclear Overhauser
effect (NOE) were performed. If the anti,anti-conformation shown
in Scheme 3 left dominates, no NOE peak can be observed for
the protons H1/H2 and H1/H3. Unfortunately protons H3 and H6
show overlapping multiplets in the 1H NMR in DMSO[D6],
hampering quantitative assessment of NOE signals (Figure S1-2
in the SI). The rotation around the C(pyridazyl)-C(triazolyl) axis
(torsion angle φ) is hindered and accordingly, 3b predominantly
populates the anti-conformation in DMSO[D6] solution, as shown
in Scheme 3. For a qualitative direct comparison, the NOE
spectrum of 3c (Figure S2) shows strong NOE signals for the
protons H1/H3 and H1/H6 because fast rotation around the N-
C(aryl) axis (angle ν) can be assumed. In contrast, this is not the
case for 3b, in which the neighboring C-F···H interaction favors
the anti-conformation, resulting in very weak NOE signals
To create helically folded backbones and generate materials
with potentially high electron mobilities, facile rotation about
sigma bonds leading to twisted (hetero)aromatics is not
desirable. In compounds 3a-h, the torsion angles (φ) connecting
the central pyridazine and neighboring triazole units
(C(pyridazyl)-C(triazolyl) axis) should display characteristic
minima and the BTPN core is expected to strongly favor the anti-
conformation (Scheme 3). The second pair of torsion angles (ν)
between the interior triazoles and terminal phenyl units should
also display a conformational bias, in particular in case of ortho-
fluorine substitution.[8]
R4
R4
R3
R2
R3
R2
R5
R5
N
N
R5
R5
N
N
N
N

R4
R3
 N N

'
R4
R3
N
N
N
N

'
R1
R1
R1
R1
N
N N
N
R2
R2
anti,anti-conformation
syn,syn-conformation
Scheme 3. Conformational preferences of BTPNs: Torsion angles φ and ν are defined by the twist of the triazole plane with regard to the plane of the central
pyridazine and terminal phenyl units, respectively.
For internal use, please do not delete. Submitted_Manuscript
This article is protected by copyright. All rights reserved.

10.1002/asia.201701277
Chemistry - An Asian Journal
FULL PAPER
perpendicular transition state that connects the global minimum
with two local minima. The latter enable -conjugation but suffer
vanishing NOE-signals
H2
from strongly repulsive interactions between the neighboring N-
atom's lone pairs as well as the pyridazine and triazole H-atoms.
To further quantify the conformational analysis (see also Figure
S3), the relevant stationary points on the reaction path around
N
N
N
N
N
N
H3
N
N
H4
H5
H1
H1
F
F
3b
the torsion angle
φ, i.e. global and local minima as well as the
H6
connecting transition state, were calculated. The computed
Gibbs energies verify the previous findings, however
underestimate the energy of the transition states and
overestimate the energy of the minima. These results clearly
verify the predominant anti-conformer in the gas phase by DFT
calculations.
Subsequently, the rotation around the N-C(aryl) axis, i.e. ν,
was elucidated by focusing once again on the key compounds
for each group (Figure 3). The first group is represented by 3a
vanishing NOE-signal
two strong NOE-signals
H2
N
N
N
N
N
H3
N
N N
H4
H5
H1
H1
H6
3c
F
F
Figure 1. Observed NOE signals for key compounds 3b and 3c.
and includes all other compounds only bearing protons in ortho
-
position (3a, 3c, 3d and 3f). This group is characterized by two
local minima of equal energy, avoiding C-H···H-C repulsion by
slightly twisting to ca. 25°. The separating barriers originate from
rotating towards a 90° perpendicular geometry, where steric
Computational studies. All structures were investigated by
DFT calculations at HSEh1PBE/6-31+G(d,p) level of theory[15] to
elucidate the presented system comprehensively (see Table S1
in the SI for angles and bond lengths of 3a-3h). The rotational
energy barrier for the rotation around the C(pyridazyl)-
C(triazolyl) axis was exemplarily calculated for 3a,b and 3e
(Figure 2).
hindrance is minimal yet the penalty of lost
becomes maximal.
-conjugation
Figure 3. Conformational preference of terminal phenyl units: Total energy as
a function of the rotation around the N-C(aryl) axis (torsion angle ) for key
compounds bearing no (3a), one (3b) or two fluorine substituents (3e) in ortho-
position, respectively. Bars (right axis) indicate the Gibbs energy for the
relevant stationary points.
Figure 2. Conformational preference of central BTPN core: Total energy as a
function of the rotation around the C(pyridazyl)-C(triazolyl) axis (the torsion
angle φ) for key compounds bearing no (3a), one (3b) or two fluorine
substituents (3e) in ortho-position, respectively. Bars (right axis) indicate the
Gibbs energy for the relevant stationary points for 3a.
The second group consists of all compounds bearing one
F-atom in ortho-position (3b and 3g). In line with the first group,
the rotation to approximately 0° is unfavorable but in contrast to
group one, two global minima exist at around 25° when the
steric hindrance induced by the larger fluorine atom is minimal
but the possibility of forming an attractive C-F···H interaction is
As expected, the rotation of the triazole ring with respect to
the pyridazine core is largely independent from the potential
fluorine substituents in ortho-position on the attached phenyl
groups. In all cases, the global minimum was found around 0°,
given. When angle
 approaches 90°, again the loss of -
corresponding to maximum
-conjugation. Potential steric
conjugation is responsible for the rise of total energy, leading to
local minima at 123°. The largest penalty is observed when the
F-atom's and the opposite N-atom's lone pairs face each other,
repulsion in the coplanar geometry is minimized due to the
favorable angles of five-membered rings adjacent to six-
membered rings (in strong contrast to biphenyl for example).[16]
Upon rotation leading to an increasingly twisted system, energy
which is not even remotely compensated by the gain in
-
conjugation. The third group consists of BTPNs bearing two F-
atoms in ortho-position (3e and 3h). Ortho-disubstitution leads to
gained from
-conjugation is gradually lost until the
For internal use, please do not delete. Submitted_Manuscript
This article is protected by copyright. All rights reserved.

10.1002/asia.201701277
Chemistry - An Asian Journal
FULL PAPER
a drastically different overall horseshoe-like shape of the
With regard to crystal packing, the six pyridazines presented
herein display all common solid-state packing motifs (Figure 5),
namely herringbone-like packing (3e), 1D lamellar packing (3a,
3c, 3d), and 2D lamellar packing (3b, 3g). Thus deliberately
choosing the fluorine-substitution pattern of the terminal phenyl
moieties provides full control over the resulting solid-state
structure.[17]
molecules, as the global minima for torsion angle
ν are located
at about 60°. The loss of -conjugation seems to be

compensated again by the seemingly large steric penalty, also
observed in the second group. Overall the F-atoms induce both
an attractive C-F···H contact as well as a repulsive interaction
between the F- and N-atoms, leading to a slightly smaller barrier
in comparison to the second group. These computational results
for the gas phase are confirmed by experimentally determined
solid-state structures (vide infra).
The observed supramolecular organization in the crystalline
solid is most likely originating from intermolecular C-H···[18] as
well as C-F···H interactions.[19] A common motif observed herein
is the interaction of the N-atoms of one pyridazine ring with the
H-atoms of a neighboring pyridazine ring (ca. 2.52 Å) leading to
their coplanar orientation and thus formation of 2D layered
arrangements. Compounds 3a, 3c, and 3d, displaying 1D
lamellar packing, furthermore engage in close -stacking of the
central pyridazine with triazole rings of adjacent molecules in
distances of 3.57 Å and 3.60 Å (centroid-to-centroid distances)
and close -stacking without offset in the case of 3c (3.60 Å).
Single crystal X-ray structure analyses. The solid-state
structures of six compounds, 3a-e and 3g, were elucidated by X-
ray diffraction of suitable single crystals. All obtained structures
are collected in the SI together with selected geometrical
parameters (listed in Table S6) and crystallographic details.
Again, we focus here on the solid-state structures of key
compounds 3a, 3b, and 3e as depicted in Figure 4. While
compounds 3a and 3e show nearly coplanar geometry at the
core, compound 3b is somewhat twisted (
based on the computation, the ortho,ortho'-difluorophenylated
derivative 3e strongly deviates from planarity with regard to the

= 15°). As expected
The structures of 3b and 3g, exhibiting 2D lamellar packing, in
contrast are largely dominated by C-F···H (2.56–2.73 Å) and C-
H···N interactions (2.58–3.01 Å). The same holds true for
compound 3e, which shows a variety of interlayer C-F···H
second torsion angle
(φ = 51°/45°). Please note that the
observed angle deviations originate either from crystal packing
effects or from differences of the structures in each phase, which
is difficult to distinguish.
contacts (2.56–3.01 Å) as close -stacking contacts are not
feasible. The unit cell and additional images illustrating the
plethora of these intramolecular weak interactions are depicted
in the SI (Figure S6-21) and constitute
a detailed and
comprehensive study of such interactions in this class of
heteroaromatic compounds.
Figure 4. Geometries of the key compounds 3a (top), 3b (middle), and 3e
(bottom) as obtained from single-crystal X-ray structure analyses and
corresponding torsion angles φ and ν.
Figure 5. Packing motifs in the crystalline solid involve: 1D lamellar packing for 3d (left), herringbone-like packing for 3e (middle), and 2D lamellar packing for 3g
(right).
For internal use, please do not delete. Submitted_Manuscript
This article is protected by copyright. All rights reserved.

10.1002/asia.201701277
Chemistry - An Asian Journal
FULL PAPER
Conclusions
Material properties. After having investigated both the intra- as
well as intermolecular interactions manifested in conformation as
well as packing, we investigated their influence on the optical
and electronic properties of all BTPN derivatives (3a-h) and their
data is summarized in Table 1. No solvatochromism was
observed when dissolving 3b in common organic solvents, such
as MeCN, MeOH or DCM. Furthermore, neither fluorescence nor
phosphorescence emission was observed. The absorption
spectra of 3a-h (see Figure S4 in the SI) all follow similar
features with a maximum hypsochromic shift of 15 nm in 3h as
compared to 3a. However, since fluorine substitution usually
lowers both the HOMO and the LUMO energy level, a strong
shift of the band gap is not expected and the changes observed
might also correspond to the geometry changes of the
molecules upon fluorine substitution, i.e. the torsion angles
By employing a highly modular click synthesis approach we
have developed a convenient pathway to synthesize BTPN
derivatives with defined conformational preferences, which
govern their structure in solution and control their packing in the
solid state. The highly conserved anti-conformation of the central
pyridazine core provides access to extended building blocks with
wide angles that should allow for the design of foldamer hosts
with large interior diameters suitable for host-guest chemistry
with big guest molecules.[10,11] Furthermore, the flat molecular
geometry in combination with specifically introduced fluorine
substituents allows for control over the supramolecular
organization in the crystalline solid. In particular in view of the
electron-poor character of the BTPN scaffold such exquisite
engineering of the packing should prove advantageous to
custom tailor these n-type organic semiconductors as electron-
affecting the extent of -conjugation.
All compounds except 3b exhibit quasi-reversible and
irreversible cyclic voltammetric responses in DMF (see Table 1).
Observed reductions occur between -1.9 to -2.0 V in DMF and
are largely independent from the fluorine substitution pattern.
transporting
(opto)electronic devices.
/ hole-blocking materials for applications in
However, the half potential (E1/2) of the reduction of 3h bearing
Experimental Section
pentafluorophenyl groups is shifted by 0.1 V towards higher
potentials relative to its perhydrogenated analogue 3a. It should
be pointed out that due to the irreversibility, the onset values are
difficult to determine, the conservative approximations lead
therefore to similar energies for the LUMO of the compounds
studied herein (ca. 2.35 eV). Additional cyclic voltammetric data
using acetonitrile or THF for molecules, which could sufficiently
be dissolved in these solvents, is compiled in the SI (see Figure
S5 and Table S4). Although reductions remain irreversible, a
clear trend can be observed for cyclic voltammetric responses in
acetonitrile, where observed reductions shift drastically to lower
potential upon fluorine substitution.
General information, all experimental procedures, compound
characterization data of all new compounds and additional data (UV/vis
spectroscopy, calculations, X-ray analyses and electrochemical details)
is contained in the supporting information. CCDC-1571320 (3a), 1571315
(3b), 1571318 (3c), 1571319 (3d), 1571317 (3e) and 1571316 (3g)
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.
General procedure for preparation of aromatic azides:[7a] The
respective aniline (20.8 mmol, 1 eq.) was suspended in 400 mL of 17%
aqueous HCl at room temperature. Ethanol was added until a clear
solution was obtained (usually a ratio of 5:1 (aqueous HCl / EtOH) was
necessary). The mixture was cooled to 0 °C. NaNO2 (41.6 mmol, 2 eq.)
was added in small portions (attention, release of toxic gas!) and the
reaction mixture was stirred for 15 min at 0 °C. Then NaN3 (41.6 mmol,
2 eq.) was added in small portions and the mixture stirred for 1 h at 0 °C.
The solution was transferred into a separation funnel, water was added
and the aqueous phase was extracted with 150 mL of ethyl acetate or
diethyl ether (4 x). The combined organic phases were washed with
water, aqueous NaHCO3, sat. aqueous NaHCO3 solution, and brine.
After drying over MgSO4, careful removal of the solvent using a rotary
evaporator (some azides are more volatile than others) gave a yellow oil
of the respective azide.
Table 1. Summary of electronic and optical properties of BTPN derivatives.
UV/Vis
electrochemistry
DFT
Epc in
V[SCE]
MeCN
Epc in
V[SCE]
DMF
ELUMO in
eV
HSEh1PB
E/6-
31+G(d,p)
max
[nm]
3a
3b
3c
3d
3e
3f
286
279
283
274
273
286
< -2.7
-1.930 (qr)
-1.944 (r)
-1.925 (qr)
-2.000 (qr)
-1.931 (i)
-2.35
-2.34
-2.36
-2.28
-2.35
-2.38
-2.04
-2.10
-2.22
-2.15
-2.02
-2.45
-2.459
-
-
-
-
General procedure of the copper catalyzed 1,3-dipolar
cycloaddition:[7a] 3,6-Diethynylpyridazine 1 (1 eq.), the respective aryl
azide (3 eq.), sodium ascorbate (0.2 eq) and TBTA (0.1 eq.) were
dissolved in a solvent mixture of H2O/tertBuOH/CH2Cl2. This mixture was
degassed and CuSO4 was added (stock solution, 10 mg CuSO4 per
0.1 mL water) and stirred for one to five days at room temperature in the
dark. After the starting material was consumed, as indicated by TLC
monitoring (product formation was indicated by a spot on or near the
baseline), the mixture was transferred to a centrifuge tube (24 mm OD,
30 mL capacity) and washed with 5 mL of 0.05 M aqueous EDTA
solution, water, CH2Cl2, CH3CN, and MeOH (4000 rpm for 10 min).
Removing of the solvent in vacuo gave the products as colourless solids
in high analytical purities. The reaction was usually run on a mmol scale.
-1.900 (qr)
3g
277
-2.287
-2.000 (qr)
-2.28
-2.36
-2.28
3h
271
-2.145
-1.919 (i)
-2.45
Summary of electronic and optical properties. Absorption of the compounds 3a-h in
acetonitrile [c(3a)
4.201·10-5 M, c(3b) = 3.452·10-5 M, c(3c) 1.189·10-5 M, c(3d)
saturated solution, c(3e) = 4.303·10-5 M, c(3f) = 3.087·10-5 M, c(3g) = 4.108·10-5 M, c(3h) =
=
=
=
3.439·10-5 M]. Electrochemical cathodic peak potentials, (r)
= reversible, (qr) = quasi
reversible, (i) = irreversible: c = 1 x 10-3 mol/L in 0.1 M Bu4NPF6 DMF, Pt-disc d = 1mm,
dE/dt = 1 V/s, ELUMO= -e (Epc vs Fc/Fc+) –4.8 eV.
For internal use, please do not delete. Submitted_Manuscript
This article is protected by copyright. All rights reserved.

10.1002/asia.201701277
Chemistry - An Asian Journal
FULL PAPER
Acknowledgements
[14] J. M. Birchall, R. N. Haszeldine, A. R. Parkinson, J. Chem. Soc. 1962,
4966.
[15] The functional of Perdew, Burke and Ernzerhof (PBE) is known for its
general applicability and gives usually accurate results for a wide range
of systems. Although the Heyd–Scuseria–Ernzerhof (HSE) screened
The authors thank Dr. B. Ziemer (HU Berlin) for carrying out the
initial single-crystal X-ray measurements. B.M.S. thanks the
Alexander von Humboldt Foundation for continuous support.
Generous support by the German Research Foundation (DFG
via SFB951) is gratefully acknowledged.
hybrid was designed for solids, the HSE functional provides
a
reasonably accurate treatment of small and medium-sized molecules
while significantly reducing computational effort; B. G. Janesko, T. M.
Henderson, G. E. Scuseria, Phys. Chem. Chem. Phys. 2009,11, 443-
454.
Keywords: click chemistry • conformation analysis • fluorine •
[16] J. Jia, H.-S. Wu, Z. Chen, Y. Mo, Eur. J. Org. Chem. 2013, 611-616.
[17] a) K. Zhou, H. Dong, H.-L. Zhang, W. Hu, Phys. Chem. Chem. Phys.
2014, 16, 22448-22457; b) B. M. Schmidt, A. K. Meyer, D. Lentz,
CrystEngComm 2017, 19, 1328-1333.
triazole • pyridazine
[1]
a) C. W. Tornøe, C. Christensen, M. Meldal, J. Org. Chem. 2002, 67,
3057-3064; b) V. V. Rostovtsev, L. G. Green, V. V. Fokin, K. B.
Sharpless, Angew. Chem. Int. Ed. 2002, 41, 2596-2599; Angew. Chem.
2002, 114, 2708-2711.
[18] M. Nishio, Y. Umezawa, K. Honda, S. Tsuboyama, H. Suezawa
CrystEngComm 2009, 11, 1757-1788; M. Nishio, CrystEngComm 2004,
6, 130-158.
[19] a) R. Fröhlich, T. C. Rosen, O. G. J. Meyer, K. Rissanen, G. Haufe, J.
Mol. Struct. 2006, 787, 50-62; b) T. S. Thakur, M. T. Kirchner, D. Bläser,
R. Boese, G. R. Desiraju, CrystEngComm 2010, 12, 2079-2085, c) D.
Chopra, T. N. Guru, CrystEngComm 2011, 13, 2175-2186; d) J. Shang,
N. M. Gallagher, F. Bie, Q. Li, Y. Che, Y. Wang, H. Jiang, J. Org. Chem.
2014, 79, 5134-5144.
[2]
[3]
a) A. Michael, J. Prakt. Chem. 1893, 48, 94-95; b) R. Huisgen, R. Knorr,
L. Möbius, G. Szeimies, Chem. Ber. 1965, 98, 4014-4021.
a) V. K. Tiware, B. B. Mishra, K. B. Mishra, N. Mishra, A. S. Singh, X.
Chen, Chem. Rev. 2016, 116, 3086-3240; b) C. S. McKay, M. G. Finn,
Chem. Biol. 2014, 9, 1075-1101; c) V. D. Bock, H. Hiemstra, J. H. Van
Maarseveen, Eur. J. Org. Chem. 2006, 51-68; d) W. Xi, T. F. Scott, C. J.
Kloxin, C. N. Bowman, Adv. Funct. Mater. 2014, 24, 2572-2590; e) A.
Qin, J. W. Lam, B. Z. Tang, Chem. Soc. Rev. 2010, 39, 2522-2544; f) Y.
Li, M. Pink, J. A. Karty, A. H. Flood, J. Am. Chem. Soc. 2008, 130,
17293-17295; g) Y. Hua, A. Flood, Chem. Soc. Rev. 2010, 39, 1262-
1271; h) B. Schulze, U. S. Schubert, Chem. Soc. Rev. 2014, 43, 2522-
2571.
[4]
a) D. Schweinfurth, L. Hettmanczyk, L. Suntrup, B. Sarkar, Z. Anorg.
Allg. Chem. 2017, 643, 554-584; b) S. Hohloch, D. Schweinfurth, M. G.
Sommer, F. Weisser, N. Deibel, F. Ehret, B. Sarkar, Dalton Trans.
2014, 43, 4437-4450; c) D. Schweinfurth, S. Demeshko, S. Hohloch, M.
Steinmetz, J. G. Brandenburg, S. Dechert, F. Meyer, S. Grimme, B.
Sarkar, Inorg. Chem. 2014, 53, 8203-8212; d) R. Maity, S. Hohloch, M.
van der Meer, B. Sarkar, Chem. Eur. J., 2014, 20, 9952-9961; e) S.
Hohloch, C.‐Y. Su, B. Sarkar, Eur. J. Inorg. Chem. 2011, 3067-3075.
a) W. S. Horne, C. A. Olsen, J. M. Beierle, A. Montero, M. R. Ghadiri,
Angew. Chem. Int. Ed. 2009, 48, 4718-4724; Angew. Chem. 2009, 121,
4812-4818; b) Y. L. Angell, K. Burgessa, Chem. Soc. Rev. 2007, 36,
1674-1689.
[5]
[6]
[7]
a) E. Yashima, K. Maeda, H. Iida, Y. Furusho, K. Nagai, Chem. Rev.
2009, 109, 6102-6211; b) E. Yashima, N. Ousaka, D. Taura, K.
Shimomura, T. Ikai, K. Maeda, Chem. Rev. 2016, 116, 13752-13990.
a) R. M. Meudtner, S. Hecht, Angew. Chem. Int. Ed. 2008, 47, 4926-
4930; Angew. Chem. 2008, 120, 5004-5008; b) R. M. Meudtner, S.
Hecht, Macromol. Rapid Commun. 2008, 29, 347-351.
[8]
[9]
D. Zornik, R. M. Meudtner, T. El Malah, C. M. Thiele, S. Hecht, Chem.
Eur. J. 2011, 17, 1473-1484.
It is possible to lock the syn,syn-conformation of BTPs using metal ions,
see: M. Ostermeier, M.-A. Berlin, R. M. Meudtner, S. Demeshko, F.
Meyer, C. Limberg, S. Hecht, Chem. Eur. J. 2010, 16, 10202-10213; b)
R. M. Meudtner, M. Ostermeier, R. Goddard, C. Limberg, S. Hecht,
Chem. Eur. J. 2007, 13, 9834-9840.
[10] a) J. Becerril, J. M. Rodriguez, I. Saraogi, A. D. Hamilton in Foldamers:
Structure Properties and Applications (Eds.: S. Hecht, I. Huc), Wiley-
VCH, Weinheim, 2007, pp. 195-229; b) G. Guichard, I. Huc, Chem.
Commun. 2011, 47, 5933-5941.
[11] a) B. Happ, G. M. Pavlov, E. Altuntas, C. Friebe, M. D. Hager, A. Winter,
H. Görls, W. Günther, U. S. Schubert, Chem. Asian J. 2011, 6, 873-
880; b) S. E. Bodman, C. M. Fitchett, Dalton Trans. 2014, 43,12606-
12613; S. E. Bodman, A. C. Crowther, P. B. Geragthy, C. M. Fitchett,
CrystEngComm 2015, 17, 81-89; c) N. Rahanyan, S. Duttwyler, A.
Linden, K. K. Baldridge, J. S. Siegel, Dalton Trans. 2014, 14, 11027-
11038.
[12] S. Achelle, N. Plé, D. Kreher, F. Mathevet, A. Turck, A.-J. Attias,
Heterocycles 2008, 75, 357-374.
[13] E. F. V. Scriven, K. Turnball, Chem. Rev. 1988, 88, 297.
For internal use, please do not delete. Submitted_Manuscript
This article is protected by copyright. All rights reserved.

10.1002/asia.201701277
Chemistry - An Asian Journal
FULL PAPER
Entry for the Table of Contents
Layout 1:
FULL PAPER
Clicking a pyridazine core via triazole
moieties to fluoroaryl units affords
versatile electron-deficient building
blocks with defined conformational
preferences and supramolecular
organization for foldamer design and
n-type organic semiconductors.
I. Birkenfelder, J. Gurke, L. Grubert, S.
Hecht,* B. M. Schmidt*
Page No. – Page No.
Click Chemistry Derived Pyridazines:
Electron-Deficient Building Blocks
with Defined Conformation and
Packing Structure
For internal use, please do not delete. Submitted_Manuscript
This article is protected by copyright. All rights reserved.